# The sclerobionts of the Bajocian Oolithe ferrugineuse de Bayeux Formation from Calvados (Paris Basin, Normandy, France)

Gérard Breton, Manfred Jäger, Tomáš Kočí

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Gérard Breton, Manfred Jäger, Tomáš Kočí. The sclerobionts of the Bajocian Oolithe ferrugineuse de Bayeux Formation from Calvados (Paris Basin, Normandy, France). Annales de Paléontologie, 2020, 106 (1), pp.102361. 10.1016/j.annpal.2019.07.002. insu-02458979

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# The sclerobionts of the Bajocian Oolithe ferrugineuse de Bayeux Formation from Calvados (Paris Basin, Normandy, France)

Les sclérobiontes de l'Oolithe ferrugineuse de Bayeux bajocienne du Calvados (Bassin de Paris, Normandie, France)

Gérard Breton<sup>a,*<sup> b</sup></sup>, Manfred Jäger<sup>c</sup>, Tomáš Kočí<sup>d,e</sup>

## ABSTRACT

Silicified fossils collected in ploughed fields at Gavrus (Calvados, France), mainly mollusc shells, are Bajocian in age, and come from the Oolithe ferrugineuse de Bayeux Formation. The entire formation is highly condensed and most fossils are reworked. Their silicification allowed treatment with dilute hydrochloric acid. This treatment brought to light numerous encrusting sclerobionts: Porifera (3 taxa), Bryozoa (n), Polychaeta (9), Brachiopoda (n), Bivalvia (5). The borings and bioerosional traces are described using the "categories of architectural design" as defined by Buatois et al. (2017). Among the 28 ichnotaxa described (corresponding to an ichnodisparity of 14), *Planavolites wisshaki* isp. nov., *Kleithrichnus belemnophilus* igen. nov., isp. nov. and *Foggara foggara* igen. nov., isp. nov. are new. Some *Gastrochaenolites dijugus* Kelly & Bromley, 1984 borings accommodate the shell of the presumed borer *Lithophaga fabella* J.-A. Eudes-Deslongchamps, 1838. A group of *Nododendrina europaea* (Fischer, 1875) on a belemnite rostrum provides a good instance of an ichnogenetic series.

Encrusting sclerobionts and macroscopic boring and bioerosional trace-makers are
dominantly suspension feeders. The ichnofacies is a peculiar *Entobia*-ichnofacies, found in

<footnote><sup>a</sup> 6 rue des Réservoirs, 76600 Le Havre, France</footnote>

<footnote><sup>b</sup> UMR, CNRS 6118, Géosciences, université de Rennes I, 35042 Rennes cedex, France</footnote>

<footnote>* Correspondence. E-mail: gerard-breton@orange.fr.</footnote>

<footnote><sup>c</sup> Lindenstrasse 53, D-72348 Rosenfeld, Germany</footnote>

<footnote><sup>d</sup> Palaeontological Department, Natural History Museum, National Museum, Václavské náměsti 68, CZ-115 79 Prague, the Czech Republic</footnote>

<footnote><sup>e</sup> Ivančická 581, Praha 9 – Letňany CZ-199 00, the Czech Republic</footnote>
deeper, lower-energy environments than the “classical” coastal *Entobia*-ichnofacies, on deep shell-grounds far from the coast, in the deep euphotic zone.

## RESUME

Les fossiles silicifiés recueillis dans les labours à Gavrus (Calvados, France), principalement des coquilles de mollusques, sont d'âge bajocien, Formation de l'Oolithe ferrugineuse de Bayeux. Toute la formation est fortement condensée et la plupart des fossiles sont remaniés. Leur silicification autorise un traitement à l'acide chlorhydrique dilué. Cette décalcification a révélé de nombreux sclérobiontes encroûtants : spongiaires (3 taxons), bryozoaires (n), polychètes (9), brachiopodes (n), bivalves (5). Les perforations et traces de bioérosion sont présentées en suivant les « catégories de style architectural » définies par Buatois et al. (2017). Parmi les 28 ichnotaxons décrits (correspondant à une ichnodisparité de 14), *Planavolites wisshaki* isp. nov., *Kleithrichnus belemnophilus* igen. nov., isp. nov. et *Foggara foggara* igen. nov., isp. nov. sont nouveaux. Dans quelques perforations *Gastrochaenolites dijugus* Kelly & Bromley, 1984, on retrouve la coquille du perforant présumé *Lithophaga fabella* J.-A. Eudes-Deslongchamps, 1838. Un groupe de *Nododendrina europaea* (Fischer, 1875) sur un rostre de bélemnite fournit un bon exemple d'une série ichnogénétique.

Les encroûtants, perforants et producteurs de bioérosion macroscopiques sont pour la plupart des suspensivores. L'ichnofaciès est une variété de l'ichnofaciès à *Entobia*, dans un environnement plus profond et d'énergie plus faible que l'ichnofaciès à *Entobia* côtier classique, sur un fond coquillier profond, loin de la côte, dans la zone euphotique profonde.

**Keywords** : Trace fossils, sclerobionts, bioerosion, polychaete tubes, silicification, Bajocian, Normandy.

**Mots clés** : Traces fossiles, sclérobionte, bioérosion, tubes de polychètes, silice, Bajocien, Normandie.
# 1. Introduction

Since the mid-19th century, the Bajocian beds of the Calvados department (Normandy, Western Paris Basin) and especially the Oolithe ferrugineuse de Bayeux Formation (abbreviated as OFB Fm. herein), have been internationally famous for their palaeontological content, mainly molluscs including a high diversity of ammonites.

D'Orbigny (1851: 606) chose the type of his Bajocian stage in Normandy, and designed the localities around Bayeux (Latin *Bajoce*, hence the name of the stage) and between Bayeux and Caen (Calvados) as the typical sites of the Bajocian stage (Rioult, 1964). Although the I.U.G.S. recently selected the Portuguese locality of Cabo Mondego as the stratotype of the Bajocian (Pavia & Enay, 1997), the Calvados department remains the historical stratotype of the Bajocian. It provided a very important range of fossils studied and often figured by different authors such as d'Orbigny (1842-1851; 1850); J.-A. Eudes-Deslongchamps (1849); E. Eudes-Deslongchamps (1865); Brasil (1895), who provided a list of 66 species of ammonites from the OFB Fm. from one quarry, Sully near Bayeux, Calvados, in a 4-fold stratigraphical division still in use to-day; Oppel (1856-1858); Wetzel (1924); and Arkell (1930, 1956) (see Rioult, 1964). Many French and foreign museums accommodate rich collections of Bajocian fossils from Calvados.

After the litho- and biostratigraphical studies of Rioult (1964, 1971, 1980a, 1980b), Gabilly & Rioult (1967), Rioult & Fily (1980), Rioult et al. (1991, 1997), Gauthier et al. (1996), Dugué et al. (1998), the works of Pavia (1994), Pavia & Martire (1997, 2010), Pavia et al. (2013, 2015) stressed the taphonomic history of the ammonites within the OFB Fm. to take into account the generalized reworking of fossils (resedimented and/or re-elaborated elements) and reconstruct “... their registratic succession and the chronological order of sedimentary events ...” (Pavia et al., 2015:5). This taphonomic critical analysis is applied to ammonites only, given their biostratigraphical importance. They follow the methods developed by Fernández-López (1991, 1995, 2007, 2011a, 2011b) and Fernández-López & Meléndez (1994). The taphonomic analysis is considered by these authors as an aid to a better stratigraphical approach. With the notable exception of the microperforations studied by Glaub (1994), the only mentions of trace fossils are those of *Thalassinoides* isp. or similar burrows at or under omission surfaces (Fürsich, 1971).
The aim of the present work is to introduce the Bajocian sclerobionts and their taphonomy, highlighting the trace fossils, mainly from the OFB Fm., the study of which has been somewhat neglected, receiving far less attention than the very abundant, highly diverse and stratigraphically significant body fossils.

**2. Geological context, material and methods**

The studied material has been collected from ploughed fields, in the vicinity of Gavrus, west of Caen (Calvados). The fossils, reworked in the soil, show that the beds of the subsoil extend stratigraphically from the Aalenian (Lower Mâlière.) to the Upper Bajocian (Calcaire à Spongiaires Fm.) (for a complete stratigraphical account, see Rioult et al., 1991 and Dugué et al., 1998). The upper part of the Mâlière Fm. (Lower Bajocian, *discites* and *laeviuscula* Biozones) is poorly represented in our material. The OFB Fm. begins with the so-called “Conglomérat de Bayeux” (Lower Bajocian, *humphriesianum* Biozone), and is followed by three beds with a similar lithology, a micritic limestone with ferruginous oolites, respectively *niortense*, *garantiana* and *parkinsoni* Biozones of the Upper Bajocian. The Calcaire à Spongiaires Fm. (previously Oolithe blanche Formation, Upper Bajocian, *parkinsoni* Biozone) provided few fossils for study. All the OFB Fm. is highly condensed (e.g. Rioult & Fily, 1980; Dugué et al. 1998; Pavia & Martire, 2010).

Because the fossils are mixed in the ploughed soil, their stratigraphical position can be deduced only from their matrix (Mâlière / OFB / Calcaire à spongiaires).

For gaining a somewhat more comprehensive overview of the serpulid and sabellid species of the OFB Fm., one of the authors (M.J.) studied additional specimens (not photographed) from his personal collection, collected in the 1980s' from several OFB Fm.outcrops in Calvados.

Since the originally calcareous fossils (mainly molluscs) are silicified at least in part, it is possible to treat them with dilute hydrochloric acid to remove calcium carbonate.

Pictures were taken with a camera Nikon D 90 and a macro lens, or with a Lumix G5 camera, helicoidal extension tube(s) and 50 or 25mm Photar lens on a stand. For the deepest fossils, a series of 3-20 images was processed using Zerene Stacker ®, the resulting zetagraphy along with the other images, being processed using Photoshop Elements ® for the final plates.
The images of polychaete tubes were taken with a Canon EOS 550D camera and light microscope Olympus DP70 camera (National Museum, Prague), each image of a polychaete edited in Helicon and Corel Draw 14© software.

The material studied here is deposited in the collections of the “Musée Vert”, Natural History Museum of Le Mans (Sarthe), with the index MHN LM. The registration number, for instance MHNLM 2018.3.101, applies to the substrate. If the substrate hosts several trace fossils or sclerobionts, each is distinguished using a letter e.g., MHNLM 2018.3.101A, MHNLM 2018.3.101B...

We follow the terminology proposed by Taylor & Wilson (2002) for marine organisms colonizing natural hard substrates.

Abbreviations: Fm.: formation. OFB: Oolithe Ferrugineuse de Bayeux. LV: left valve, RV: right valve. SEM: scanning electronic microscope.

**3. Remarks on the taphonomy and the mineralogy of the studied fossils**

Because these fossils were collected from ploughed soil, and not *in situ* from the OFB Fm., no analyses of their relationships with the sedimentary environment is possible and thus no complete taphonomic analysis. Moreover, the taphonomic conditions may differ from one bed to another. Our remarks are therefore limited to those directly deduced from the fossil itself. Whatever their taxonomic identities, most (if not nearly all) fossils of the OFB Fm. are reworked, and the majority of them are re-elaborated *sensu* Fernández López (2011b). The re-elaborated fossils had more than one period of residence on the sea-bed: first during their life (for the epibenthic species), then after their death, with or without displacement and after a possible exhumation following burial, before their final burial. During all these steps, shells can be disarticulated, broken, encrusted by episkeletobionts, and bored by diverse endoskeletobionts. Complete criteria for recognizing re-elaboration of ammonites are given, for instance, by Pavia et al. (2013: 140). Between their death and final burial, the fossils underwent two major mineralogical changes: (1) silicification of most of the originally calcareous skeletons; and (2) external encrustation by iron oxides.

The distribution and the mineralogical expression of the silica differ depending on the structure of the fossil.
1) Very thick shells. The siliceous epigenesis is restricted to a more or less thin layer of the outer and inner sides of the shells (Fig. 1 b); a thick median layer remains calcareous, rarely preserving the original lamellar structure (Fig. 1 d), sometimes with small sphaero-radiolitic growths of calcedonite (Fig. 1, arrowhead), often with recrystallized microcrystalline calcite (e.g. the limid *Ctenostreon hector* (d'Orbigny, 1850)). A *Ctenostreon hector* shell shows scale-shaped silica growths. The belemnite rostra show a peripheral thin layer of silica, from which thin needles of silica often point towards the axis of the rostrum, the centre of which retains its original radiating calcitic composition (Fig. 2 A). In both cases, the borings are also lined by a thin layer of silica.

2) Thick shells (pleurotomariids, astartids such as *Neocrassina obliqua* (Lamarck, 1819), nautilids and large ammonites) show a lace distribution of the silica, either in the form of a foam or as septa approximately perpendicular to the surface (“cloisonné” structure) (2 B, C), which are thought to be inherited from the organic frame of the prismatic layer of the shell. This situation is closely comparable to that described by Holdaway & Clayton (1982, p. 374) in Cretaceous silicified brachiopod shells: “Incompletely silicified specimens often show that silicification has proceeded lengthways along the prisms, as shown by relict calcite prisms within otherwise silicified areas of the shell”. In the case of our material, the “calcite prisms” became voids after decalcification. There are intermediate structures between the “foam” and the “cloisonné”; both can be more or less dense, tight but rarely nearly massive. When the structure is loose, the decalcified fossils are highly brittle.

3) Thin shells (brachiopods, small oysters, spondylids) are built of white fibrous chalcedony. Sometimes, fine-scale replacement (Holdaway & Clayton, 1982) leads to exquisite preservation of tiny details such as the punctae of the shells of terebratulids or the spines of *Acanthothyris spinosa* (Linnaeus, 1788) (,2-D). The external layer is sometimes made of beekite (orbicular chalcedony) (Lacroix, 1901: 147-148; Carson, 1987). Beekite also develops locally on the external layer of very thick or thick shells (cases 1 and 2) (,2-E) and belemnite guards. In one case, a late input of silica healed a broken shell of *Pseudotrapezium* sp.? without displacement.

4) Shells with chambers (ammonites, nautilids). The chambers are either filled (totally or partially) with sediment which can be similar to the matrix of the fossil (resedimented fossils) or different, for instance devoid of ferruginous oolites (reelaborated fossils). The sediment infilling the chambers, in the case of re-elaborated fossils, is generally massively silicified, with sometimes beekite on its surface. If the infilling is partial, it lays
geopetally. If the ammonite rested slightly obliquely on the bottom, the infillings of successive chambers are step-like (Fig. 2 F). If the chamber is empty (or in the void above a partial infilling) a geode is frequently observed, with, from the outside to the centre: (1) septa or shell transformed in microcrystalline chalcedonite, (2) fibrous chalcedonite ending with small quartz crystals, (3) automorphic transparent quartz crystals, often with scattered goethite needles or scales (Fig. 2 G, respectively A, B, C, D).

A late mineralogical input, which is elsewhere common in almost-outcropping platy limestones, is the deposition on the underside of a crust of calcitic cauliflower-like micro-concretions, probably what Pavia et al. (2013: 139) named "microcrystalline alabaster crust" (Fig. 1 a). This crust obscures the underlying details but is easily removed by the action of HCl and is useful to indicate the up/down initial positioning of any loose rock piece (underside of the shell downwards in Fig. 1).

In rare cases (e.g. a single specimen cf. *Sphenorhynchia plicatella*), the shell is silicified, and there is a thin silica flat "roof"; the empty shell is preserved on one side of the "roof", but not on the opposite side (Fig. 3 A: red arrow, "roof" from above (ventral): white arrow, roof from below (dorsal)). This case can document the mechanism and timing of the silicification. The original sediment was presumably reducing (see also Préat et al., 2000). In a very different sedimentological context, Breton (2006) stated that the epigenesis of calcite into silica follows a redox gradient. The *Sphenorhynchia plicatella* shell was half buried in a reducing sediment. The silica "roof" formed at the limit between the oxygen-depleted sediment (and inside of the shell, with decaying tissues) and oxygenated sea water. Why the part of the shell jutting out the sediment was dissolved is not well understood. Silicification of the rest of the shell was not necessarily synchronous with the formation of the silica "roof". The remaining part of the shell of this specimen of *Sphenorhynchia plicatella*, together with its "roof", was later re-elaborated into the unsilicified iron oolite sediment.

Another argument favours multiple silicification phases: HCl-processed blocks of iron oolite limestone (not silicified) often reveal accumulations of silicified fossils among which no fossil is calcitic. Therefore, later phases of silicification took place, as shown by the epibionts that are nearly all silicified.

Butts (2014) stated that "silica replacement affects shells at the exclusion of the matrix, indicating an organismal genesis of the process." This is not the case in our material in which the shells with chambers are partly or totally infilled with sediment which can be silicified, and in many ammonites, the umbilicus is filled with calcareous sediment on one
side, but with silicified sediment on the other side. This latter side was resting on the sediment, allowing the development of a reducing zone which favoured the precipitation of silica.

Residency of the shells on the seabed was repeated and may have lasted a long time. During these periods, the shells acted as substrates for encrusters and borers. It is difficult to demonstrate an order of colonization (see Bottjer, 1982: 82; Breton, 2017: 182), and especially to differentiate between those encrusters and borers which settled *syn-vivo*, and those which settled *post-mortem*, except for predatory traces (*syn-vivo*) or settlement on the inner surfaces of shells (*post-mortem*).

The OFB Fm. from Calvados is evidently not the only example of silicified fossils in a calcareous matrix: another Bajocian instance is the so-called “Ciret” from the Mont-d’Or Lyonnais (Rhône, France). In the case of the fossils studied herein, silicification offers both drawbacks and advantages. The drawbacks are that some fossils become very brittle after HCl processing (when the silica mesh is loose) and that tiny structures can be obscured by silica growth, especially beekite. The advantage is the magnificent preparations possible using hydrochloric acid treatment (Fig. 3 B, C) which often reveals epi- or endozoans that would have remained otherwise undiscovered or at least underestimated.

A remark is necessary concerning “taphonomic enlargement” of borings and the measurement of their diameters. The diameter of borings, especially sub-superficial, cylindrical, straight or meandering tunnels such as *Trypanites*, *Maeandropolydora*, or *Talpina*, is frequently overestimated in our material and must be regarded as approximate. This “taphonomic enlargement” is due to the brittleness of the silicified shell. For instance, tunnels of *Talpina* isp. in a pleurotomariid shell are 125-200 µm in diameter, and the internal mould of a tunnel, preserved locally (and silicified) is 75 µm in diameter. Similarly, a tunnel of *Trypanites* isp. in a shell of *Pyrgotrochus elongatus* (Sowerby, 1818) is 750 µm in diameter whereas its ferruginous internal mould is 625 µm in diameter. Another cause of approximation in these measurements is due to the precision of the eyepiece micrometre, whose divisions are 25 µm at the maximum magnification.

In the following section, the epizoans are described and introduced in a systematic order and the endobionts are treated as trace fossils.

## 4. The encrusting sclerobionts
We consider here the epibenthic organisms (only animals in the studied material) which are fixed on organic hard substrates, for instance shells. Most of them can also dwell on lithic hard substrates but the latter are beyond the scope in our work, since we had no access to OFB hardgrounds.

## 4.1. Poriferans

The sponges in our material can be attached to organic hard substrate, but conversely they also acted as hard substrates for other encrusters.

### Undetermined lithistid demosponge

The sponge is fixed on a pleurotomariid columella. Desmas are visible. The assignation to Rhizomorines is possible, but questionable.

*Neuopora spinosa* (Lamouroux, 1821)

(= *Acanthopora lamourouxi* Haime, 1854)

Fig. 3 D, E, F

Several small sponges (less than 1.5 cm), are ramifying with a round to square section of the branches and a slightly expanded base. The mould of a bivalve shell (with growth lines) is seen on one attachment surface, while a cylindrical serpulid tube, 5 mm in diameter, is visible on another specimen. Walter (1970) included neuoporid incorrectly among cyclostome bryozoans. Każmierczak & Hillmer (1974) showed that the Hauterivian species *Neuopora pustulosa* (Roemer, 1839) was a sclerosponge, and assigned it to the order Ceratoporellida. West et al. (2013) assigned the genus *Neuopora* to the order Halichondrida.

The stratigraphical distribution of *Neuopora spinosa* is broad, from the Upper Aalenian to the Upper Oxfordian. In the Calvados department, *Neuopora spinosa* is known from the Upper Bajocian (*parkinsoni* biozone) (Walter, 1970).

### Undetermined large discoid ?hexactinellid

Fig. 3 G

This sponge is tentatively assigned to hexactinellids because a small surface shows a fine striation, although lithistid demosponges, attested by the presence of desmas, can show a
similar striation (Bert & Breton, 2017: 46, fig. 13). Careful local decalcification did not show any spicules. The overall shape is discoidal, 60 to 68 mm in diameter, one side being irregularly flat. The edge is rounded, and the other side has the shape of a depressed cone (maximum thickness 25 mm). This side is intersected by a deep diametric slit, which is a fixation surface on an unidentified perished substrate, possibly an alga, roughly spindle-shaped, 50 mm long with a maximum diameter of c. 20 mm. A cylindrical oblique sinuous hole, 1 cm in diameter, starts from the slit and leads to the flat side of the sponge; it is interpreted as a branch of the substrate. The lips of the slit markedly encase the substrate, but not the flat side. If this sponge, owing to the organic substrate, is an episkeletobiont, it also acted as a substrate for sabellid epibionts, *Glomerula gordialis* (von Schlotheim, 1820) which are common on one side of the slit.

This can be compared with other specimens of ramified sponges with cylindrical stout branches, both from the OFB Fm. and the Calcaire à Spongiaires Fm., which accommodate abundant calcareous polychaetes tubes only on one side of the sponge, together with rare bryozoans. This can be explained in two ways. If colonization took place *syn-vivo*, the settlement of the larvae and the development of the polychaete tubes and bryozoans on one side of the erect sponge may have been determined by currents. If colonization occurred *post-mortem*, settlement on the side of the sponge lying on the seabed and partly buried in would have been impossible, and the epibionts developed only on the opposite side.

## 4.2. Polychaetes (by M.J. and T.K., figures by T.K.)

### Sabellidae

#### Genus *Glomerula* Brünnich Nielsen, 1931

##### *Glomerula gordialis* (von Schlotheim, 1820)

###### Fig. 4 A-D, 7 D-E

Very common. One specimen is a single *Trigonia elongata* valve encrusted by *Glomerula gordialis* on the inner as well as on the outer surface. Many of the other specimens are now loose fragments, following HCl preparation. A cylindrical segment of a branching sponge accommodates many tubes of *Glomerula gordialis*, but only on the face which is interpreted to have faced the current, at the time of the settlement of a swarm of larvae.
The morphology of *Glomerula* tubes is highly variable. The shape of these extremely long but relatively slender tubes highly depends on the availability and size of solid substrates, which comprise mainly the hard parts of marine invertebrates. In the Late Cretaceous Chalk and other fine-grained soft-bottom habitats with relatively few and mainly small-sized to tiny substrates, *Glomerula* tubes (Cretaceous species: *G. serpentina* (Goldfuss, 1831)) tend to build compact tube morphologies by bending in tight curves in order to become closely adnate (though not firmly cemented) to their own posterior tube portions, resulting in meanders, spirals and chaotic 3D-knots (hence the name of the Jurassic species!). In the Jurassic, such tube morphologies but more often *Glomerula* settling on large bivalve shells had a wide available space and often also a long time due to low sedimentation rate, to spread all over the surface of their substrate, thereby forming long and only slightly curved tubes. For such extensive, 2-D or low-3-D, space-consuming morphotypes the valid species name *G. flaccida* (Goldfuss, 1831) is available (for example, Ippolitov 2007a). However, we consider this to be only an ecological variant of *G. gordialis*.

## Serpulidae

### Genus *Metavermilia* Bush, 1905

### *Metavermilia goldfussi* Ippolitov, 2007a

Fig. 4 E-F

Not common.

Several different *Metavermilia* species, including a five-keeled species, plus a morphologically similar *Filogranula* species, occur at other localities in the Bajocian of Normandy (M.J., personal observation). However, at the locality of Gavrus only a single *Metavermilia* species has been detected, *M. goldfussi*, which is small, three-keeled and more or less rectangular or only slightly trapezoidal in cross-section.

### Genus *Cementula* Regenhardt, 1961

### *Cementula* sp. 1

Fig. 4 G-I
Common. At other localities in the Bajocian of Normandy, these tubes are found attached to different substrate species, often to an undetermined species of large, near-planar, non-ornamented bivalve shells.

These small, simple, non-ornamented spiral and non-spiral tubes of Middle Jurassic age may usually be affiliated to: *Cementula circinnalis* (Münster in Goldfuss, 1831) (the type is from the earliest Aalenian); or *C. filaria* (Goldfuss, 1831) for which Goldfuss mentioned localities of Middle Jurassic as well as Oxfordian age; or, *C. oligospiralis* (Ippolitov, 2007b) (the type is from the Callovian). Small spiral tubes from Gavrus and other Bajocian localities in Normandy may well belong to one of these species. If badly preserved, *Cementula* sp. 1 can be difficult to be distinguished from small spiral specimens of *Glomerula gordialis*.

### *Cementula* sp. 2

Fig. 4 J-K

Not common. Two spirals are attached to a single fragment of a pleurotomarid gastropod.

Medium-sized, distinctly ornamented spirals with smoothly "molten" turns, and a few non-spiral tube portions. Tube base wide. Ornament is always present but varies considerably among the relatively few available specimens from different Bajocian localities in Normandy due to original variability plus patterns caused by diagenetic silification and treatment with HCl.

Unfortunately, due to either fragmentary preservation or, at other Bajocian localities, encrustation by other tubes and sediment, it is difficult to follow the course of these tubes backward to check if younger ontogenetic stages are ornamented or not. Nevertheless, it seems more probable that *Cementula* sp. 1 and sp. 2 represent distinct species than different ontogenetic stages of a single species.

### Serpulidae gen. et sp. indet.

Fig. 5 A

Pieces of rock showing characteristic mass occurrences of this species are not common, but on such pieces many tubes may be present, together with a few basal remains of
larger tubes, possibly *Propomatoceros lumbricalis* forma "limax", attached to one side of a
sponge.

Tubes are small, irregularly curved, unornamented, and increase only slowly in
diameter. They resemble those of the sabellid *Glomerula*, but differ by not forming sharp
curves or knots and by showing no tendency towards thigmotactic adhesion to the posterior
parts of their own tubes or to other tubes. Affiliation to the serpulid genus *Filograna* may be
possible, but there is no tendency to form bundles composed of many more or less parallel
aligned tubes. Affiliation to genus *Cementula* is also possible, and indeed many tube portions
are hardly distinguishable from true *Cementula* when individuals of both taxa settled nearby
on the same substrate. However, in dense populations of the present species the total or near-
total lack of spirals and peristomes strongly argues against determination as *Cementula*.

Genus *Propomatoceros* Ware, 1975

*Propomatoceros lumbricalis* (von Schlotheim, 1820) **forma "limax"** (Goldfuss, 1831)

Fig. 4 L-N

Very common. In some of the numerous specimens, the tubes are attached to sponges,
to *Ctenostreon hector*, *Neocrassina obliqua*, *Pleurotomaria armata* Münster in Goldfuss,
1840, a poorly preserved ammonite, or an unknown substrate.

Medium-sized to large tubes, increasing in diameter at a moderate rate, consisting of a
long, irregularly curved, serpentine or loop-forming posterior portion attached to a substrate
by a well-developed, moderately wide base lacking tubulae, often followed by a short or long,
straight or slightly curved free portion.

Longitudinal ornament consists of a single element and is very variable. Usually a
single keel of variable size and shape is present, rarely undulating and/or developed as a high
comb, in the posterior portion, but becoming weaker or disappearing or turning into a
longitudinal furrow in the anterior part of the attached posterior portion or in the free tube
portion. Transverse ornament consisting of incremental lines and weakly to moderately
developed peristomes or bulges may be present or lacking. In the attached tube portion,
transverse ornament often slightly protrudes at the median line, less often it protrudes more
distinctly or not at all. However, the free tube portion of medium-sized to large specimens usually ends with a smooth, spineless aperture somewhat restricted in outer tube diameter.

Also the tube cross-section varies between specimens and ontogenetic stages, ranging from triangular with convex latera in the posteriormost parts to normally inverse U-shaped in adult attached portions or subcircular to circular in the free anterior portion. Tube wall moderately thick to thick in large tubes.

The oldest available species name of this group of serpulids is *Serpulites lumbricalis* von Schlotheim, 1820, a name published without a figure that united specimens from several geographically and stratigraphically widespread localities. Ippolitov (2007b) discussed and confirmed the validity of this species. Goldfuss (1831) introduced several species names for representatives of this group, providing figures and more detailed geographical and stratigraphical data. Several of Goldfuss' species came from the Bajocian of southern Germany, probably the *humphriesianum* zone. Both Parsch (1956) and Ippolitov (2007b) considered *Serpula limax* Goldfuss, 1831 and *S. grandis* Goldfuss, 1831 subjective synonyms of *S. lumbricalis*. Unfortunately, as already stated by Ippolitov (2007b), the combination *Serpula limax* as introduced by Goldfuss (1831) is a junior homonym of *Serpula? limax* Defrance, 1827. Here we use Goldfuss's species names as informal names: 'forma "limax"' and 'forma "grandis"'. One of us (M.J.) is still uncertain if *limax* and *grandis* represent only different ontogenetic stages of a single species or rather two different species, with *grandis* differing from *limax* in overall size, thick tube wall, more common and conspicuous transverse bulgings slightly protruding at median line, and up to three weak additional longitudinal furrows at the latera and on the underside. Although no detailed measurements and statistics have been made, it is often possible to sort samples of Bajocian to Callovian ages into a few huge "forma *grandis*" and many medium-sized to moderately large "forma *limax*".

While "forma limax" is very common, "forma grandis" is lacking in the material from Gavrus, but occurs in low numbers of specimens at other localities of the OFB Fm. and is common in the overlying white limestomes of the latest Bajocian Calcaire à Spongiaires Fm. in the coastal cliffs of Normandy.

Genus *Mucroserpula* Regenhardt, 1961

*Mucroserpula cf. tricarinata* (J. de C. Sowerby, 1829)
Fig. 5 E

Not common.

Medium-sized tubes increasing in tube diameter at a moderate to fast rate, attached for most or all of their length. Three keels of which the median keel may be somewhat more prominent and is situated in a higher position. Incremental lines or delicate transverse striation may be present or lacking, somewhat protruding at the median keel. Cross-section pentagonal, forming a trapezium with an additional edge on top.

Unfortunately, Regenhardt (1961) designated a small, presumably juvenile, and uncharacteristic specimen as holotype of the type species *Mucroserpula mucroserpula* Regenhardt, 1961. It is uncertain whether or not this specimen would have become a morphologically typical *Mucroserpula* if it had grown older. Unfortunately, its type locality is no longer accessible, so that no additional specimens could be collected there to study older ontogenetic stages.

Also unfortunately, Regenhardt (1961) expressly stated that tubes of the genus *Mucroserpula* are attached for all of their lengths; in other words, that a free anterior tube portion does not exist. However, photographs of the two other species of *Mucroserpula* described and figured by Regenhardt (1961) show not only three keels and a pentagonal cross-section, two morphological features typical for *Mucroserpula*, but also the presence of a long free (although presumably not steeply elevated) tube portion at least in *Mucroserpula versabunda* Regenhardt, 1961.

Therefore, in spite of uncertainties concerning the holotype specimen of the type species, *Mucroserpula* is considered a valid genus which includes species possessing (with a few exceptions) the following tube morphology: small to very large tubes increasing in tube diameter at a moderate to fast rate, attached for most of its length to a substrate although some species possess a free tube portion. Attached tube portion with three keels of which the median keel is the most prominent and situated in a somewhat higher position, whereas lateral keels may be weaker or developed as rounded edges only. Free tube portion with five or six keels. Cross-section of attached tube portion pentagonal, forming a trapezium with an additional edge on top. Main occurrence in the Jurassic and Early Cretaceous, but also recorded from the Late Maastrichtian.

*Mucroserpula* sp. 1 or *Pyrgopolon* (*Septenaria*) sp.?
Fig. 5 B-C

Not common. One specimen is attached to *Ctenostreon hector*.

Tube medium-sized, attached tube portion bearing three keels. Free tube portion rising steeply with pedestal-with-cave-construction at base, bearing five keels which end as protruding spines at the aperture. Details of morphology and tube structure obscured by coarse-grained silification.

In outer morphology this tube resembles the genus *Pyrgopolon* de Montfort, 1808, especially the subgenus *Pyrgopolon* (*Septenaria*) Regenhardt, 1961. However, in most *Pyrgopolon* specimens the keels do not form protruding spines at the aperture, although exceptions exist. Moreover, no special features of either *Pyrgopolon* (*Septenaria*) (*Favosites* structure, honeycomb ornament, specialized tabulae) or *P*. (*Pyrgopolon*) and other subgenera (chambered tubulae, inner tube layer often becomes separated from outer tube wall after death) can be recognized, and it is unknown if these features were lacking in the original tube or were obscured by coarse-grained silification. Since an operculum of *Pyrgopolon* has been found in the Permian of Sicily (Sanfilippo et al., 2017), it is logical that this genus must have existed in the Jurassic.

*Mucroserpula* sp. 2

Fig. 5 F-G

Not common.

Tube medium-sized to large. Three robust keels of more or less equal sizes. Distinct transverse ornament consisting of robust and prominent striation. Although the anteriormost tube portions are broken off, they probably became free from substrate, although rising obliquely at a low angle only.

This species differs from *M*. cf. *tricarinata* by its slightly larger size, more robust keels and, most of all, from both *M*. cf. *tricarinata* and *M*. sp. 1 by the more robust and more prominent transverse ornament.

Genus *Nogrobs* de Montfort, 1808

*Nogrobs vermicularis* de Montfort, 1808
Fig. 5 D

Rare. A single fragment of the free tube portion.

*Nogrobs quadrilatera* (Goldfuss, 1831) is the attached tube portion of what is presumed to be the same species.

### 4.3. Bryozoans

*Stomatopora cf. dichotomoides* (d'Orbigny, 1850),

cf. *Reptomultisparsa cricopora* (Vine, 1881)

Fig. 6 A, B

Cyclostome bryozoans are fairly common episkeletozoans and can be found on bivalves, gastropods, nautilid and belemnite guards. Some are exceptionally well preserved, but in others the upper sides of the zooecia are abraded or silicification obscures the morphological details. Most are either “Berenicea”-like sheet encrusters or *Stomatopora* sp. runner encrusters. One example is a specimen found on the inner side of a valve of the limid *Ctenostreon hector*, hence representing *post-mortem* colonization after disarticulation of the valves. Another specimen (?*Hyporosopora* sp.) is on a chamber wall of the nautilid *Cenoceras* sp., and thus also a *post-mortem* settler. Two specimens on belemnite guards have been tentatively identified as *Stomatopora cf. dichotomoides* (d'Orbigny, 1850) (Fig. 6 A) and cf. *Reptomultisparsa cricopora* (Vine, 1881) (Fig. 6 B) by Paul D. Taylor (NHMUK, London, in litt. 08/01/2018 and 23/02/2018).

Walter (1970: 243, 244) cited five species described by d'Orbigny (1850) from the Upper Bajocian of Calvados (Calcaire à Spongiaires Fm.), to which he added ten species from his own collections.

### 4.4 Brachiopods

*Moorellina (Elliottina) dubia* (d'Orbigny, 1850)

Fig. 6 C, D

Tiny ventral valves of thecideid brachiopods are found on both sides of bivalve valves and on belemnite guards (Fig. 6 C, D). The ventral valves, cemented to the substrate, are most frequently preserved, whereas dorsal valves are very rarely preserved (one occurrence).
According to Pajaud (1970), *Moorellina (Elliottina) dubia* (d'Orbigny, 1850) is the only thecideid species in the Bajocian of Normandy. E. Eudes-Deslongchamps (1857) reported the occurrence of “Thecidea dubia ?? d'Orb., 1847” in the Upper Bajocian “oolithe blanche” [=Calcaire à spongiaires Fm.], but not in the OFB Fm. The best preserved ventral valves of thecideids in our material are consistent with such an identification, which has been confirmed by Marc Chesnier (in litt. 06/02/2018). Only examination of the characters of the inner sides of dorsal valves can provide a more certain identification.

A small terebratulid is fossilized in a chamber of *Entobia geometrica* Bromley & D'Alessandro, 1984. Its two valves are closed, lack infilling, and its pedicle is oriented towards the ceiling of the chamber. Therefore it is believed to be a settler, living in a cryptic habitat that was fossilized in life position, and not a shell deposited with the sediment.

### 4.5. Bivalves

#### Oysters

Fig. 6 E, F, G

Oysters are a common component of the sclerobiont community.

Oyster sp. A has shells measuring 10-20 mm, frequently found on the outer sides of the valves of *Ctenostreon hector* where they settled *syn-vivo*. Settlement on inner sides of the valves of bivalves (*Ctenostreon hector*, *Trigonia elongata*), or on the umbilical area of a large oppeliid ammonite, is far less frequent and could have taken place *post-mortem*. Most are poorly preserved: the part of the shell close to the substrate is preserved but the rest of the LV, in relief, is not. Moreover, the pertinent morphological characters are obscured by the growth of beekite. The anterior part of the shell, when preserved is gently arched, perpendicular to the substrate and bears 6-11 ribs.

Oyster sp. B comprises one LV with an estimated height of 30 mm but incomplete, the ventral side forming a wall 20 mm high, devoid of ribs, perpendicular to the substrate, fixation surface 20x15mm, possibly a flat bivalve shell, adductor muscle pad in relief (Fig. 6 E). The fixed part of the valve is perforated by a small *Oichnus simplex* Bromley, 1981 that reaches the adductor muscle pad (Fig. 6 E, arrows). This specimen is silicified in beekite, and shows branching polychaete perforations (*Maeandropolydora isp.?*). Another specimen (not figured) of the same size showing the same characters was found.
Lophiinae *Lopha ? hastellata* (von Schlotheim, 1820) is represented by one specimen, a LV, 34 mm height, 22 mm long, with a small concave fixation surface, c. 20 radiating ribs, adductor muscle pad hidden by the fixation, on the inner side of the shell, of at least two generations of oysters sp. B. (Fig. 6 G). Another specimen is fixed on a *Ctenostreon hector* shell. Another partial LV of the same species, far less well preserved, hosts a serpulid tube on the inner side of the valve. An incomplete RV of the same species (57x35 mm preserved) shows the axial xenomorphic sculpture of a cylindrical, supposed initially vertical support on which this RV was fixed (Fig. 6 F). This example is morphologically identical to the living *Lopha folium* (Linnaeus, 1758) attached to a gorgonacean twig as figured by Stenzel (1971: fig. J47).

## Other bivalves

Fig. 6 H

**Cemented bivalves.** One specimen of *Atreta* sp., with its fixed valve (RV) in the furrow between two ribs of a large *Ctenostreon hector* and a broken LV. A specific identification is not possible. Abraded fixed valves of oysters, spondylids?, dimyids? are numerous, but unidentifiable.

**Byssiferous bivalves.** They are considered here as epolithozoans or episkeletozoans according to Taylor & Wilson's (2002) nomenclature. But the cases where the substrate and the bivalve remain associated are rare in the fossil record unlike, for instance, cemented bivalves. A good example is provided by a young parallelodontid, *Cosmetodon hirsonensis* (d'Archiac, 1843), the two valves of which, though slightly displaced, are preserved in the hollow of a belemnite phragmocone (Fig. 6 H). Its length is estimated as 1314 mm. The bivalve obviously settled not only after the death of the belemnite, but after the dissolution of the thin septae of the phragmocone, i.e. during a late phase of reworking of the belemnite rostrum. The infilling of the phragmocone by sediment prevented the dislocation of the valves of the bivalve.

## 5. Borings and bioerosional traces.

Numerous attempts have been made to classify trace fossils at a supra-generic rank, including morphological, preservational or ethological criteria. To introduce the perforations
made by endoskeletobionts in the Bajocian shells, we have followed the categories of
architectural design as defined by Buatois et al. (2017), which provide a good framework, less
formal but not more subjective than any other morphological-ethological based classification.
The number given by Buatois et al. (2017) to each category of architectural design is shown in
brackets following its name.

5.1. *Horizontal branching burrow systems (16): Arachnostega isp. cf. A. gastrochaenae* Bertling, 1992

*Arachnostega isp. cf. A. gastrochaenae* Bertling, 1992

Fig. 7 A

Although *Arachnostega* isp. cf. *A. gastrochaenae* is a burrow and not a boring, it is
introduced here for three reasons.

1. This mud-dweller trace is found at the surface of yhe internal casts of bivalves, meaning that it was produced close to the inner side of the shells and so can be considered as associated with the shell as hard substrate.

2. This traces occur in reworked, and mainly re-elaborated fossils *sensu* Fernández López (2011b), some of which were already lithified when bored: the difference between boring and burrowing is weak here.

3. When found in internal casts of reworked and silicified molluscs, *Arachnostega* isp. cf. *A. gastrochaenae* can be silicified too, and our method of preparation (HCl process) allows to be exposed in exactly the same way as the silicified borings.

*Arachnostega* isp. cf. *A. gastrochaenae* is common, either as an unsilicified or a
silicified trace fossil in internal casts of bivalves (Astartidae, *Pholadomya* sp., *Pleuromya* sp.,
*Plagiostoma* sp., *Trigonia elongata*, *Myoconcha crassa* Sowerby, 1824...), in the living
chambers or phragmocone chambers of the cephalopods *Cenoceras* sp. and *Chondroceras*
*evolvescens* Waagen, 1867, in the internal casts of large brachiopods *Loboidothyris cf.*
*perovalis* (Sowerby, 1825), *Sphaenorhynchia plicatella* (Sowerby, 1821), and in internal casts
of pleurotomariid gastropods where it is at least partly silicified (Fig. 7 A). In our material, it
is found from the Upper Mâlière Fm. to the Calcaire à Spongiaires Fm.

**Remarks.** The preparation of our specimens by HCl etching confirms that *Arachnostega* isp. cf. *A. gastrochaenae* is not confined to the 2-D interface between the shell
and its infilling, but extends as branches into the thickness of the sedimentary infilling (Bertling, 1992: p. 180). This feature can be missed using the classical approach of examining internal casts, which highly favour observation only of the interface trace (Bertling, 1992; Damborena & Mancenido, 1996 among others). At the ichnospecific level, our trace shows differences compared with *A. gastrochaenae*: the slow increase in diameter by a factor 5 to 10 has not been recorded here. It has thus been placed in open nomenclature within this currently monospecific ichnogenus.

## 5.2. Cylindrical vertical to oblique borings (59): Trypanites Mägdefrau, 1932

These cylindrical borings are straight or nearly straight, with a constant diameter throughout, never meandering, with no U-turns, silicified as tubes, sometimes with a ferruginous infilling, and are found in thick shells. They are identified as *Trypanites* isp. Their diameter is: 0.8 mm on a pleurotomariid (two borings from the apex to the last whorl); 0.6-1.2 mm on several *Neocrassina obliqua* valves; 0.9-2.5 mm on *Ctenostreon hector*; 0.9 mm on the ventral edge of a valve of *Trigonia elongata*, where it is cut by an *Oichnus simplex* boring; 0.5-0.6 mm on *Belemnopsis* sp. guards. On thick shells such as *Neocrassina obliqua*, the opening is always on the margin of the shell. The boring is constrained by the thickness and the convexity of the shell or the belemnite rostrum. It runs subsuperficially and is exposed by erosion of the external layer of the shell. When only a small part of the course of the boring is exposed, it is not possible to decide if the boring is *Trypanites* isp. or a straight part of *Maeandropolydora* isp. Although we did not observe any inflated distal ends, it is not possible to discard its identification as the ichnogenus *Paleosabella*.

Several pleurotomariids show one to three apical perforations. They are possibly short *Trypanites* because X-ray study did not reveal any winding around the columella like those characteristic of the ichnogenus *Helicotaphrinus* Kern, Grimmer & Lister, 1974.

## 5.3. Winding borings (61): Lapispecus Voigt, 1970 and Maeandropolydora Voigt, 1965

A straight portion of a tube, 0.8 mm in diameter, 4 mm long, is separated from part of the rostrum of the belemnite *Belemnopsis* sp. It is referred with doubt to the ichnogenus *Lapispecus* Voigt, 1970 because of the presence of an ill-defined longitudinal vane.
Meandering perforations of a constant diameter are identified as *Maeandropolydora isp.* They play a major role in the bioerosion of belemnite guards and to a lesser extent that of bivalve shells. Their diameter is 1.0 mm in the shell of an oyster *Gryphaea (Bilobissa) sublobata* (Deshayes, 1830) [Mâlière supérieure Fm., Lower Bajocian]. In the thick shells of *Ctenostreon hector*, their diameter is often 0.9-2.0 mm but can reach 3.0 mm; these borings number 8 to 10 per shell. They open at the rim of the shell and their course seems to favour the ribs of the shell, where the thickness of the shell is greatest. In the belemnite guards, their diameter is smaller (0.5-1.4 mm). One cuts a *Calcideletrix* isp., whereas other are ramifying.

5.4. *Circular holes and pit-shaped borings (63): Cyclopuncta girtyi Elias, 1958, Planavolites wisshaki isp. nov.*, Oichnus simplex *Bromley, 1981, and a healed wound.*

*Cyclopuncta girtyi* Elias, 1958

Fig. 7 B, C

*Cyclopuncta girtyi* was first described from an Oklahoman Devonian cephalopod shell (Girty, 1909: pl. VI, fig. 6) and named and correctly considered as a boring by Elias (1958: 50-51, figs. 14, 16). We have found similar borings that we have dubbed “raindrop pits”. The external surface of a *Ctenostreon hector* valve shows numerous small pits, 0.4-0.9 mm in diameter and 0.4-0.6 mm deep (Fig. 7 C). Each individual pit, on average, is round to slightly oval with a vertical wall and a nearly flat to slightly concave bottom. The pits are scattered across the whole shell, with densities varying from 12 to 40 pits/cm². They are distributed irrespective of the region or the ribs and furrows of the shell. The pits are well separated from each other, with the exception of two coalescent pits. The other sclerobionts on this shell are: *Gastrochaenolites dijugus* Kelly & Bromley, 1984, *Rogerella mathieui* de Saint-Seine, 1956, *Talpina* isp. of 0.15 mm diameter, oysters, serpulids and sabellid tubes and bryozoans. The latter are not affected by *Cyclopuncta girtyi* which are thus early borings, presumably settled syn-vivo.

A second *Ctenostreon hector* bears “raindrop pits” with the same density as the first one, but these pits are obviously shallower (0.1-0.3 mm). A dense group of “raindrop pits” is located on the inner side of a third small *Ctenostreon hector*, denoting a post-mortem settling (Fig. 7 B)
A group of about thirty *Cyclopuncta girtyi* pits are found on the inner side of an *Astarte elegans* Sowerby, 1816 shell (MHNLM 2018.3.17). They range from 375 to 625 µm in diameter, their estimated depth is 200-500 µm, and their bases are concave. Other bioerosional traces are found on the same inner side of this shell: *Talpina isp.*, *Orthogonum isp.*, *Calcideletrix flexuosa* Mägdefrau, 1937, together with sabellid and serpulid tubes.

On the flat basis of a pleurotomariid shell, about thirty *Cyclopuncta girtyi* show an extreme variation in the diameter of 150-750 µm. They are scattered across a 12 x 7 mm surface (MHNLM 2018.30.16).

A *Belemnopsis* sp. rostrum, of which one side is weathered by meteoric alteration, shows on the preserved side shallow “raindrop pits” of *Cyclopuncta girtyi* 0.25-0.6 mm in diameter, slightly smaller than those on *Ctenostreon hector* but of the same morphology. Therefore, the rims of these “raindrop pits” are chamfered but these pits with such blunt rims are grouped on the belemnite rostrum while other pits have vertical walls that cut the surface of the rostrum at right angles. We believe that such a blunt rim is not an intrinsic character of the trace, but results from the dissolution of the calcite of the rostrum and is thus considered taphonomic. These *Cyclopuncta girtyi* perforations in this belemnite rostrum are overgrown by polychaete tubes, bryozoans and thecideids and are cut by the circular apertures of a probable *Talpina* isp., 0.15 mm in diameter. Thus they are thought to represent an early generation of borings in the rostrum.

Other groups of *Cyclopuncta girtyi* are located on the top of the ribs of a *Ctenostreon hector*, on the outer side of a bivalve shell fragment, on other *Belemnopsis* guards. This ichnospecies is thus not rare in our material.

These groups of borings – circular pits and globular borings – which include the ichnogenera *Planobola* Schmidt, 1992, defined from SEM observations, *Tremichnus* Brett, 1985, bored into echinoderm ossicles, the much larger *Circolites* Mikuláš, 1992, *Kardopomorphos* Beuck, López Correa & Freiwald, 2008, together with *Cyclopuncta* Elias, 1957 are in need of a revision. The ichnogenus *Cyclopuncta* is retained here for our “raindrop pits” since it fits better with our material (size, shape and distribution on the bored shell) but this choice does not prejudice any ichnotaxonomic conclusion about a possible synonymy.

*Planavolites* Mikuláš, 1992

*Planavolites wisshaki* isp. nov. (by G.B.)
Fig. 7 D, E, F

**Etymology.** This ichnospecies is named in tribute to Dr. Max Wisshak (Senckenberg Research Institute) for his outstanding contribution to bioerosional ichnology.

**Type material.** Holotype: on a *Neocrassina obliqua* shell, MHNLM 2018.3.32, Fig. 7 D, E and F (H). Paratypes. A cluster of depressions of various sizes on a *Neocrassina obliqua* shell, MHNLM 2018.3.15, Fig. 7 F (P1). A group of small depressions on an astartid shell, MHNLM 2018.3.36, Fig. 7 F (P2). One small depression on a bivalve shell fragment, MHNLM 2018.3.34, Fig. 7 F (P3).

**Type locality.** Gavrus, west of Caen (Calvados, Normandy, France).

**Type horizon.** Oolithe ferrugineuse de Bayeux Formation, Bajocian.

**Diagnosis.** Millimetre to centimetre-sized very shallow depressions on shells. The outline is rounded in small specimens, to irregularly lobate in larger ones. The floor is flat and connects to the surface of the shell by a concave slope which can locally be moderately steep but never forms a perpendicular or overhanging wall.

**Description.** The holotype is located on the outer side of a well-preserved but broken 50 mm high left valve of *Neocrassina obliqua*. A first part of the bioerosional trace is an elongate, shallow depression with well-marked sides, approximately 24 x 9 mm wide, lobate in outline. This depression is widely connected with another one, larger but shallower, with limits becoming gradually less precise towards the beak of the shell. Possible faint radulation traces are very locally visible under a low angle of incidence illumination, but none can be ascertained. On the floor of the bioerosional trace, several openings, c.170 µm in diameter, are attributed to *Talpina* isp. The remains of encrusting polychaetes, one small oyster and a bryozoan are very badly preserved, except for a meandering tube of the sabellid *Glomerula gordialis*.

The paratypes MHNLM 2018.3.15 are located on the outer side of a right valve of a *Neocrassina obliqua*, preserved with its valves closed. The larger depression is elongate (18 x 7 mm), shallow, with a lobate outline. The floor is poorly preserved (granular silicification) but was originally even. This main depression is surrounded by several smaller ones, from 1 mm in diameter with a rounded outline to an elongate, lobate, 9 x 4mm. The paratypes MHNLM 2018.3.36, located on the outer side of an astartid shell, comprise four rounded millimetre-sized depressions, three of which are coalescent and surrounded by five very small rounded depressions. Another group of two depressions, 4 mm apart, is less well defined.
Dendrinids *Calcideletrix* isp. and *Dictyoporus nodosus* and polychaete tubes are preserved next to the depressions.

The paratype MHNLM 2018.3.34 is located on the outer side of a bivalve shell fragment measuring about 1 cm², close to a *Calcideletrix flexuosa* overgrown by a sabellid tube. It is a vaguely lobate depression, measuring 4 x 3 mm.

**Comparison with other ichnotaxa.** The new ichnospecies fits well the diagnosis of the ichnogenus. It can be distinguished from the only other ichnospecies of this ichnogenus known to date, *Planavolites homolensis* Mikuláš, 1992 by the lack of pointed projections and by the connection between the floor of the trace and the surface of the shell which is a gently concave slope and never a vertical or overhanging wall. Moreover, *P. wisshaki* is notably shallower than *P. homolensis*: 1 mm deep for traces of 24 or 18 mm wide (*P. wisshaki*) vs 10-15 mm for traces of 50 mm wide (*P. homolensis*) (Mikuláš, 1992). Lastly, *P. homolensis* occurs on the surface of a firm limestone according to Mikuláš (1992) whereas *P. wisshaki* is located on the outer side of thick bivalve shells.

**Remarks.** Though not very abundant, our material shows a developmental series from the smallest depressions, rounded or faintly lobate, to larger lobate depressions, the largest examples being lobate, elongate, with coalescent areas. The specimen MHNLM 2018.3.15 bears different developmental stages: the main depression has the same characters as the holotype and is surrounded by small, more or less rounded or lobate depressions. This developmental series could be considered as an ichnogenetic series *sensu* Belaústegui et al. (2016) if the development of the trace was directly related to the development of the boring behaviour of the trace-maker. But the identity of the trace-maker remains unknown.

Since this bioerosional trace is very shallow, it could be considered at first glance as an attachment trace, which would argue against its placement in architectural category 63 (circular holes and pit-shaped borings). The developmental series and, if confirmed, the faint radulation traces of the holotype, discard the “attachment trace” hypothesis. At the same time, it questions the place of *Planavolites* within category 63: Mikuláš (1992) evoked chitons, gastropods and echinoids as trace-makers. We have provisionally placed *Planavolites wisshaki* into category 63, waiting for new finds and further research.

We have few finds of this ichnospecies in our material, all on HCl-processed shells. But its frequency is probably underestimated because the smallest traces may be overlooked and even larger traces may not be recognized when the preservation is not good, for instance
if the floor of the bioerosional trace and the neighbouring areas are made of coarse granular silica: in this case, the trace will likely be considered mechanical or preservational.

**Stratigraphical and geographical range.** These data are restricted to the material described herein: Bajocian (Oolithe ferrugineuse de Bayeux Formation), Gavrus (Calvados, France).

*Oichnus simplex* Bromley, 1981

Fig. 8 A

In our material, *Oichnus simplex* is mainly found in bivalve shells, mostly in *Neocrassina obliqua* but rarely in the pleurotomariid *Obornella granulata* (Sowerby, 1818). The diameter of the hole varies from 1.2 to 2.5 mm. One *Oichnus simplex* boring, located near the ventral side of the valve, cuts through a dendrinid. Another specimen of *Oichnus simplex* is found in a small astartid, not completely perforating the valve, which thus could alternatively and formally be considered as a *Tremichnus* cf. *excavatus* (Donovan & Jagt, 2002) devoid of central raised boss, and located in a bivalve (Donovan & Jagt, 2002; Wisshak et al., 2015). Another specimen (1.3 mm in diameter) is located close to a ventral side of a valve of *Trigonia elongata*. A last small specimen (0.5 mm in diameter) of *Oichnus simplex* perforates the substrate on which an oyster was cemented (substrate not preserved) and reaches the adductor muscle pad (Fig. 6 E, arrows). A large *Oichnus simplex* (Fig. 8 A), 2.5 mm in diameter, perforates the robust shell of an *Obornella granulata*, half a turn from the peristome.

Healed wound

Fig. 8 B

A circular hole, 3.5 mm in diameter, with an irregular floor, is located on the upper side of the shell of the pleurotomariid *Obornella granulata* half a turn from the peristome (Fig. 8 B). A swelling faces the hole on the inner side of the shell. It shows that this hole is a healed wound. We do not address this wound to an ichnotaxon, because we do not know if the original boring drilled the shell throughout (though it likely perforated it) and because the morphology of its wall is badly preserved. But it compares well with the large *Oichnus*
*simplex* (Fig. 8 A) described above, because both are large and similarly located half a turn of the peristome.

5.5. *Globular to spherical borings (64) to Radial borings (74): a survey of the microborings of the OFB Fm. described by Glaub (1994).*

Glaub (1994) described fifteen microperforational ichnotaxa or forms from the Bajocian OFB Fm., on shells, *Sphaeroidothyris* sp., *Neocrassina* sp., *Astarte tipha* d'Orbigny, 1850, shell fragments and *Pseudomelania* sp. from Sainte-Honorine-des-Pertes (Calvados). She processed her material with the so-called cast-embedding technique and examined it under an SEM.

The following ichnotaxa or forms are recorded by Glaub (1994) from the Bajocian shells, OFB Fm. from Sainte-Honorine-des-Pertes.

- Globular to spherical borings (64). *Planobola macrogota* Schmidt, 1992.

- Clavate-shaped borings (66). *Cavernula coccidia* Glaub, 1994.

- Branched tubular borings (68). *Ichnoreticulina elegans* (Radtke, 1991); *Ichnoreticulina* sp. 1.

- Non-camerate network borings (69). *Orthogonum tubulare* Radtke, 1991; *Orthogonum fusiferum* Radtke, 1991; *Orthogonum lineare* Glaub, 1994; *Orthogonum giganteum* Glaub, 1994; *Orthogonum appendiculatum* Glaub, 1994.

- Camerate network borings (70). *Saccomorpha clava* Radtke, 1991; *Saccomorpha terminalis* Radtke, 1991.

- Camerate boxwork borings (72). *Entobia*-Form 2.

- Radial borings (74). *Polyactina araneola* Radtke, 1991; ? "*Palaeoconchocelis starmachii*" Campbell, Kaźmierczak & Golubic, 1979;

and, possibly referred to “cylindrical vertical to oblique borings (59), a “Makrotubular-Form”.

This survey enhances the known ichnodiversity of the OFB Fm. Therefore, the results of the decalcification process and the cast-embedding technique followed by an SEM examination are not comparable and may be distorted, the latter favouring the smallest perforations which are obviously less (or not) preserved by the silicification (see the conclusion below). That is
why we have grouped Glaub's (1994) results here, and in the following sections, we resume
the description of the bioerosional traces from our material.

5.6. *Pouch borings* (65): Rogerella de Saint-Seine, 1951

This very common acrothoracican barnacle boring is pouch-shaped, commonly
grouped on various calcareous biological substrates. The apertures are straight to comma-like,
longer than wide, and sometimes exhibit a peduncular slit at the anterior side of the aperture.
We agree with Bromley & D'Alessandro (1987), Bromley (1992), Fürsich et al (1994) and
Buatois et al. (2017) that *Rogerella* is a senior synonym of the following barnacle boring
ichnogenera: *Brachyzapfes* Codez & de Saint-Seine, 1958, *Simonizapfes* Codez & de Saint-
Seine, 1958, *Zapfella* de Saint-Seine, 1954 and *Seminolithes* Hyde, 1953. The differences
between these ichnotaxa are at most of ichnospecific rank.

*Rogerella elliptica* (Codez & de Saint-Seine, 1958)

Fig. 8 C

**Remarks.** Codez & de Saint-Seine (1958) mentioned Codez (1957) as the author of this ichnospecies, as well as the author of the ichnogenera *Brachyzapfes* and *Simonizapfes*. However, the work of Codez (1957) remained unpublished and the first valid publication is Codez & de Saint-Seine (1958).

We identify as *Rogerella elliptica* common perforations in the bivalves *Ctenostreon hector*, *Trigonia elongata* and other unidentified bivalves, the gastropods *Pyrgotrochus elongatus* and *Pseudomelania lineata* (Sowerby, 1818), and belemnite guards (*Belemnopsis* sp.) on the basis of a lack of peduncular slit, of a depth (D) of the boring less than the length (L) of the aperture (D=0.5 to 0.9 L), and of a short chamber. The chamber of *Rogerella elongata* (Codez & de Saint-Seine, 1958) is much longer. The smallest apertures are 0.5 x 0.2 mm, the largest 3.1 x 1.1 mm and a mean size is 1.8 x 0.3 mm.

On *Ctenostreon hector*, *Rogerella elliptica* is located preferentially on the ridge of the ribs and their apertures are oblique or perpendicular to the rib (Fig. 8 C). A small *Pyrgotrochus elongatus* accommodates 117 borings of *R. elliptica*, nearly all of them located on the posterior bulge of the whorls.

Though Codez & de Saint-Seine (1958) quoted *R. elongata* on *Belemnopsis sulcatus*
(Miller, 1826) from the Bajocian of Bayeux, we did not find any boring showing such a long
chamber. So, we assigned all the borings on *Belemnopsis* guards to *R. elliptica*. The stratigraphical range of *R. elliptica*, restricted to the Lower Cretaceous by Codez & de Saint-Seine (1958), is thus extended to the Bajocian.

*Rogerella mathieui* de Saint-Seine, 1955

Fig. 8 D

We identify as *Rogerella mathieui* borings into specimens of the gastropods *Pleurotomaria mutabilis* Eudes-Deslongchamps, 1848 and *Pseudomelania lineata* (Fig. 8 D), the brachiopod *Sphenorhynchia plicatella* and a rostrum of the belemnite *Megateuthis* sp., on the basis of the presence of a reasonably well preserved peduncular slit, at least in some borings, the depth of the boring being greater than the length of the aperture, and the short chamber. The smallest apertures are 0.6 x 0.2 mm, the largest 3.1 x 0.5 mm and a mean size is1.9 x 0.4 mm. According to de Saint-Seine (1956), the ichnospecies is known from the Jurassic, but only on echinoids. One of us has described *R. mathieui* on Albian and Cenomanian plicatulid and oyster shells (Breton 2011, 2017). The nature of the substrate of *R. mathieui* is thus wider and includes also gastropods, brachiopods, bivalves and belemnites. In the shell of a large *Pleurotomaria mutabilis*, 37 mm high, ten *R. mathieui* borings are located only on the posterior bulge and at the apex. The largest borings are in the posterior whorls, and the smallest in the apical whorls. A very incomplete, very thin (0.5-1.2 mm) shell of the brachiopod *Sphaenorhynchia plicatella* accommodates about 30 *R. mathieui* borings. The borings are very oblique in order to provide space enough for their growth.

### 5.7. Clavate-shaped borings (66): Gastrochaenolites Leymerie, 1842

We follow Kelly & Bromley (1984) for the descriptive terminology.

*Gastrochaenolites dijugus* Kelly & Bromley, 1984

Figs. 7 C, 8 E, F, G

*On Neocrassina obliqua*

Two specimens of *Gastrochaenolites dijugus* are bored into the thick valve of this bivalve. Their chambers are adjoining and are respectively 7 mm and 9 mm in diameter. The apertures open on the inner side of the valve, near the hinge. The apertures are figure-of-eight
shaped and are respectively 2.8 x 1.7 mm and 5.0 x 2.0 mm. The neck of the latter is curved. The apertures located on the inner side of the valve indicate a *post-mortem* boring. Another fragment of a *N. obliqua* valve, very poorly preserved, shows two chambers of *Gastrochaenolites* isp., 5 mm and 7 mm in diameter. They cannot be identified ichnospecifically.

On *Ctenostreon hector*

Nine specimens of *Ctenostreon hector* accommodate *Gastrochaenolites* borings. The number of borings per fossil, from both visible chambers and apertures, is given, followed between brackets by the estimated number per complete valve: 3 (6); 19 (40); 3(3); 10 (10); 20 (20); 14 (14); 15 (30); 10 (40); 5 (25).

The section of the chamber is always circular. The diameter of the chambers ranges from 3 mm to 10 mm, the size is generally homogeneous on a single valve of *C. hector* but in rare cases, it may vary for instance from 3 to 7 mm on a single valve. A large chamber measures 9 mm in diameter and is 20-22 mm long. In rare cases, the bottom of the chamber reaches the inner side of the shell. Bioglyphs corresponding with the original lamellar structure of the shell can be seen on the wall of most chambers. The apertures are figure-of-eight shaped (Fig. 8 E, arrow, see also Fig. 7 C). The smallest ones are 2.5 x 1.0 mm, the largest 4.0 x 2.0 mm, a common size being 3.0 x 1.5 mm. The apertures are located on the outer side of the shell, preferentially (two-thirds of the borings) on the ridge of the ribs. The aperture of one specimen only is located on the ventral margin of the shell. No calcareous lining is preserved in our material, which may be due to our HCl processing.

The silicified shell of the borer is preserved within the chamber in twelve cases (Fig. 8 E, arrowhead, 8 F). The size of the shell fits well the boring, indicating that the bivalve is the borer and not a squatter as in the case of *Hiatella* discussed by Kelly (1980). Though incomplete, the bivalves preserved in the *Gastrochaenolites dijugus* perforations fit well with *Lithophaga fabella* J.-A. Eudes-Deslongchamps, 1838. J.-A. Eudes-Deslongchamps (1838: 228) stated that his new species is present (but rare) in “Epaisseur des valves du *Lima proboscidea*, Sow. du calcaire à oolites ferrugineuses des Moutiers” [Thickness of the valves of *Lima proboscidea*, Sow. (=Ctenostreon proboscideum) from the limestone with ferruginous oolites at Les Moutiers]. The fossilization of the bivalve borer inside the boring is not rare: examples are described, among others, by Bromley & Asgaard (1993), Fürsich et al. (1994), Donovan (2002, 2015), Donovan & Hensley (2006), and Donovan & Jagt (2013).
*Gastrochaenolites lapidicus* Kelly & Bromley, 1984?

On *Ctenostreon hector*

When the superficial layers of the host shell are abraded, the section of the neck of *Gastrochaenolites dijugus* displays a round hole which must not be mistaken with a round aperture. Two valves of *Ctenostreon hector* accommodate both *Gastrochaenolites dijugus* and a *Gastrochaenolites* isp. with a round aperture, possibly *Gastrochaenolites lapidicus*, but this identification remains tentative, failing a correspondence between chambers and apertures. The round apertures, 1.5-2.5 mm in diameter, are located on the ribs of the shell.

*Gastrochaenolites isp.*

About eight small borings are located on both sides of a small flat calcareous pebble.
One chamber is 4mm in diameter and 8 mm long.

5.8. Branched tubular borings (68): Talpina von Hagenow, 1840 and Ichnoreticulina Radtke & Golubic, 2005.

*Talpina isp.*

Fig. 8 H

The frequency of representatives of *Talpina* in our material is certainly underestimated, since the apertures alone on an unabraded substrate do not allow a positive identification of the perforation. The subsuperficial tubular borings can be seen only when the substrate – a shell or a belemnite rostrum – is abraded. The tunnels are straight and circular in cross section with a constant diameter. Ramifications are few, branching is dichotomous to lateral, at 40-90°. The apertures are evenly spaced, round and their diameter is the same or slightly smaller than the diameter of the tunnels. This diameter is often overestimated due to a “taphonomic enlargement” (see § 3 “Remarks on taphonomy and mineralogy of the studied fossils”).

On both sides of a shell of *Ctenostreon hector*, tunnels are subsuperficial, very straight, branching at 45°. Openings and tunnels are 125-250 µm in diameter, the highest
values being due to taphonomic enlargement. Another *Ctenostreon hector* fragment
accommodates on its inner side a very similar *Talpina* isp (Fig. 8 H). On a *Belemnopsis* sp.
rostrum, the tunnels, parallel to the surface, are 125-200 µm in diameter and sparsely
branched. Their internal mould is ferruginous. Other specimens are found on gastropod shells:
*Pseudomelania* sp. (tunnels and apertures 200-250 µm in diameter) or pleurotomariids (e.g.,
*Pleurotomaria armata* with tunnels and apertures 125-200 µm in diameter, whereas the
silicified internal mould of a tunnel is 75 µm in diameter). Lastly, a poorly preserved
*Cenoceras* sp. shell accommodates, both on the shell itself and on the septae, very straight
tunnels branching at an acute angle (40°) and 200 µm in diameter (measured on a silicified
portion of internal mould). The apertures are not distinct.

The sole Jurassic ichnospecies *Talpina eduliformis* Quenstedt, 1858, as discussed by Voigt (1975), is smaller than our specimens, but its overall form of branching is similar to our material. *Talpina gruberi* Mayer, 1952, a Triassic ichnospecies, is also smaller (borings 60-150 µm in diameter) and has more flexuous tunnels (Voigt, 1975; Schmidt, 1992). The *Talpina* isp. described and figured by Voigt (1975: 149-150; pl. 14, 1-2; pl. 18: 4) seems closer to our material, though slightly smaller.

We leave our Bajocian *Talpina* isp. in open nomenclature since new material is
necessary to precise its ichnospecific placement.

***Ichnoreticulina isp.***

We identify, with reservations, as *Ichnoreticulina* isp. a microboring growing radially
in a belemnite rostrum *Belemnopsis* sp. (MHNLM 2018.3.93). The borings, filled with
ferruginous material, are 15-20 µm in diameter. Where branching is scarce, the boring is
nearly straight but where the branching is more profuse, the boring is wavy. This
*Ichnoreticulina* isp.? compares well with the “*Reticulina* sp. 1” of Glaub (1994, p. 113).

5.9. *Non camerate network borings (69)*: *Orthogonum Radtke, 1991.*

***Orthogonum giganteum*** Glaub, 1994

Fig. 8 I, K, L

This boring is preserved on belemnite guards, shells of *Ctenostreon hector*, *Astarte elegans*, other bivalves, a thick nautilid shell, and the side of the living chamber of a large
Perisphinctidae. When the filling of the boring, ferruginous material or less frequently silica, is preserved, its diameter is 25-35 µm. When there is no filling, the trace seems much larger, for instance 100 µm for a boring of 35 µm (cf. § 3: remark on the "taphonomic enlargement"). The main axes and their branches have a constant diameter. The main axes are straight or gently curved. The lateral branches are often short and alternating. Second level ramification is rare. Branching is nearly always at a right angle, more rarely by 60°. In one case, the network becomes denser on the edge of the shell fragment by the superposition of the courses of several *Orthogonum giganteum*. The longest *O. giganteum* in our material is *c*. 20 mm.

*Orthogonum appendiculatum* Glaub, 1994

On the rostrum of a *Belemnopsis* sp., this boring is 25 µm in diameter; appendices are few, 30-40 µm in diameter and in groups of two or three (MHNLM 2018.3.95).

*Orthogonum isp.*

Fig. 8 J

The two borings identified as *Orthogonum isp.* are located inside a thick *Ctenostreon hector* shell, several millimetres below the surface of the shell (MHNLM 2018.3.92). They are respectively 10 and 25 µm in diameter. Both are ferruginous (Fig. 8 J). Their course is straight, and their branching is mostly perpendicular, less frequently at 60°.

*Igen. isp.* A

Fig. 9 A

We leave in open nomenclature a superficial boring on the dorsal valve of *Sphenorhynchia plicatella*. The main axes are wavy or undulate, *c*. 75 µm in diameter (but with probable taphonomic enlargement). Branches are few.

5.10. *Camerate network borings (70)*: Saccomorpha Radtke, 1991

*Saccomorpha isp.*

Fig. 9 B-F
A small fragment (35 x 40 mm) of a thick (6-10 mm) shell of *Ctenostreon hector*, heavily encrusted by bryozoans and polychaete tubes and bored by *Maeandropolydora, Rogerella* and *Talpina*, was processed by dilute HCl. This revealed a silicified microperforation on the bottom of a cavity opening on the inner side of the shell and previously filled with limestone or calcite (Fig. 9 B). This perforation seems issue from another perforation related to the outer side of the shell. It consists of about 25 pouches, the 4 or 5 largest ones forming a central cluster and the smallest ones lined up around the central cluster. The pouches have a very thin and delicate silica wall, a flattened club shape distally conical or rounded and a basis slightly constricted. When the pouches are tightly packed, their shape may become somewhat irregular. The estimated height of an individual pouch can reach 500 µm for the largest ones, and the individual diameter is 50-250 µm.

Following mediocre imaging (Fig. 9 B), for a working document, the central part of the trace was accidentally destroyed. The remaining pouches, about 15 in number, are all small and peripheral. However, this accident revealed a tunnel, straight, 400 µm long, 10 µm in diameter, infilled with oxidized pyrite, with a geminate course over 150 µm (Fig. 9 C). The tunnel is clearly visible, thanks to a brown infilling; elsewhere, this or possible other tunnels cannot be seen. The tunnel runs exactly at the base of the large pouches of the central cluster.

In a small piece of pseudomelaniid shell (Fig. 9 D-F), over a small surface (11 x 3.2 mm), 50 well preserved similar pouches (plus 20-30 poorly individualised pouches) issue from the outer side of the shell: their bases are 250 µm apart from the outer surface of the shell. The pouches are 200-500 x 100-260 µm in diameter, and up to 600 µm in height. No tunnel can be seen here, but many pouches seem to be lined up.

**Remarks.** This microboring fits well with Radtke's (1991: 92) diagnosis of *Saccomorpha*: "Pouch-shaped cavities, with diverse shapes and sizes, generally linked by uniform, thin, thread-like tunnels" [translated from German]. It compares well with Schmidt's "Fasciculate-Form II" (Schmidt, 1992: 63, fig. 140, pl. 4, fig. 3), though the latter is significantly smaller. It is difficult to assign our trace to an ichnospecies as all published ichnospecies are smaller. In particular *Saccomorpha clava* described by Glaub (1994: 80-83, pl. 2, figs. 5, 7, pl. 3, figs. 3, 2) from the Bajocian OFB Fm. from Sainte-Honorine-des-Pertes, is much smaller and has mainly spherical pouches. We leave this *Saccomorpha*isp. in open nomenclature because the main difference with the published ichnospecies is the size, which is not a satisfactory ichnotaxobase (Bertling et al., 2006) and because little material is available in which the network is far less well exposed than the pouches.
*Cavernula* Radtke, 1991 is a pouch or clavate-shaped boring, which is isolated and not connected to any network or boxwork. *Rhopalia* Radtke, 1991 is a network, the chambers of which are spherical or club-shaped lateral or intercalary swellings (Radtke, 1991; Golubic & Radtke, 2008).

5.11. *Non-camerate boxwork borings (71): Kleithrichnus belemnophilus igen. nov., isp. nov.*
(by G.B.)

Ichnogenus *Kleithrichnus* igen. nov.

**Type ichnospecies.** *Kleithrichnus belemnophilus* isp. nov., single known ichnospecies.

**Etymology.** Contraction of the ancient Greek words *kleithron* (Κλείθρον) meaning lattice, grate, and *ichnus* which is a common ending for trace fossils names, referring to the ancient Greek *ichnos* (□χνος) meaning trace, track (Brown, 1954-1956). Gender masculine.

Diagnosis. Borings in calcareous substrates with a superficial tier of ramifying, anastomosing, often coalescent, sometimes spiny, cylindrical to flattened tunnels forming a lattice-like three-dimensional network, related to deep tiers of cylindrical tunnels, often undulating, with a smaller diameter.

*Kleithrichnus belemnophilus* isp. nov.

Fig. 10 A-C

**Etymology.** Ending -*philus* meaning which likes; *belemno* (from the ancient Greek βελεμνον meaning javelin, allusion to the shape of the belemnite guards): this ichnospecies develops mainly on belemnite guards.

**Type material.** Holotype MHNLM 2018.3.7 (Fig. 10 A). Paratypes: MHNLM 2018.3.8 to 2018.3.12, 2018.3.37 and 2018.3.41 to 2018.3.43 on belemnitid *Belemnopsis* sp. guards (Fig. 10 B, C), 2018.3.28 and 2018.3.29 on bivalve shells.

**Type locality.** Gavrus, west of Caen (Calvados, Normandy, France). Material collected in a ploughed field, 19.04.2018.

**Type horizon.** Oolithe ferrugineuse de Bayeux Formation, Bajocian
**Diagnosis.** As for the genus.

**Description.** The HCl etching process that was applied to our material may has destroyed the most superficial tiers of the borings: the type material have been selected because several tiers of the trace are represented. These borings develop at the surface of the rostrum and penetrate 0.4 mm into the rostrum.

The holotype (Fig. 10 A) is filled with silica containing few iron oxides. The main tunnels, 75 to 150 µm in diameter, are cylindrical or locally flattened parallel to the surface, irregularly branching, anastomosing. At the nodes of the network, they can be locally coalescent, the width of the coalescent areas can reach ca. 500 µm. The main tunnels are locally bristly or spiny. From the tunnels of the superficial tier arise cylindrical but very contorted offshoots, the thinnest being 15-20 µm in diameter, which penetrate c. 0.2 mm in the rostrum. The rostrum is broken, and the fracture with a displacement of about 1 mm is sealed by a veinlet of partly silicified calcite. The 3-D network is interrupted by the fracture and develops on both sides of the fracture, which thus occurred later than the development of the network.

MHNLM 2018.3.8 is also filled with silica containing few iron oxides. The main tunnels, 60-80 µm in diameter, are irregularly branching, anastomosing, coalescent at the nodes of the network, where they can be flattened. The thinnest tunnels are 30 µm in diameter.

MHNLM 2018.3.9 (Fig. 10 B) is filled with ferruginous material. The tunnels are round in cross-section, 20-30 µm in diameter. The superficial tier with flattened, anastomosing tunnels, is far less well exposed.

MHNLM 2018.3.10 (Fig. 10 C) has the same characters. A serpulid tube covering the external layer of the rostrum containing the network is locally invaded by the network, too.

MHNLM 2018.3.11 is filled with ferruginous material with few white silica parts. The main tunnels are 75-250 µm in diameter, enlarged and flattened at the nodes. From the tunnels of the superficial tier arise downwards cylindrical contorted offshoots 30 µm in diameter. The trace extends on a surface of 2 x 1.5 cm.

Other material includes, for instance, a *Belemnopsis* sp. rostrum where a well-developed *Kleithrichnus belemnophilus* partly overlaps a well-developed *Orthogonum giganteum*. (MHNLM 2018.3.13).
*Kleithrichnus belemnophilus* is found nearly always on *Belemnopsis* sp. or, less frequently, on the guards of *Megateuthis* sp. Other substrates are rare compared to the tens of infested belemnite guards. There are two poorly preserved specimens on the inner and the outer sides of a *Ctenostreon hector* shell (MHNLM 2018.3.29) and one poorly preserved and small specimen on the outer side of the shell of the pectinid *Spondylopecten subspinosus* (von Schlotheim, 1820) (MMNHLM 2018.3.28).

**Remarks.** Most of the belemnite guards were processed with dilute HCl. Even when the immersion was brief, *Kleitrichnus belemnophilus* is often restricted to the vicinity of the residues of matrix. The etching of the surface of the rostra often removes the external tier of the boring network. Therefore, we cannot rule out the possibility that the tiers of *Kleitrichnus belemnophilus* correspond to stages of ichnogenetic development of the trace (Belaústegui et al., 2016).

**Comparisons with other ichnotaxa.** The tunnels of *Chaetophorites* Pratje, 1922 and *Eurygonum* Schmidt, 1992 are circular in cross-section, have a smaller diameter, are not coalescent and do not anastomose. They are not flattened.

**Stratigraphical and geographical range.** These data are restricted to the material described herein: Bajocian (Oolithe ferrugineuse de Bayeux Formation), Gavrus (Calvados, France).

5.12. *Camerate boxwork borings* (72): Entobia *Bronn, 1837*.

*Entobia geometrica* Bromley & D'Alessandro, 1984

Fig. 10 D

A thick fragmentary valve of *Ctenostreon hector* displays a severe entobian boring, together with *Gastrochaenolites* isp. (MHNLM 2018.3.21). This *Entobia* (Fig. 10 D) is referred to the ichnospecies *Entobia geometrica* on the basis of the following characters. The apertures, on the inner side of the valve, fall into two distinct size categories, respectively *c*. 0.7 and 1.7 mm. The chambers are several millimetres to several centimetres in size. Their walls show numerous thin intercameral canals, 0.1-0.3 mm in diameter. The most delicately preserved parts show the characteristic facetted microsculpture of entobian bioerosion, sometimes superposed to the xenoglyphs of the lamellar structure of the shell. The chambers seem to be arranged on two tiers. They are highly coalescent, reaching growth phase D or E.
*Entobia isp.*

Two specimens, MHNLM 2018.3.23, in the umbonal part of a broken valve of *Ctenostreon hector* and MHNLM 2018.3.31 in a valve of *Neocrassina obliqua* do not show characters which could lead with certainty to an ichnospecific identification.

5.13. *Dendritic and rosetted borings (Dendrinidae) (75): Calcideletrix flexuosa Mägdefrau, 1937, Dictyoporus nodosus Mägdefrau, 1937, Nododendrina europaea (Fisher, 1875).*

*Calcideletrix flexuosa* Mägdefrau, 1937

Fig. 10 E, F

This boring is found on belemnite guards *Belemnopsis* sp. and on the shells of *Cosmetodon hirsonensis*, *Astarte elegans*, *Neocrassina obliqua*, a terebratulid brachiopod, and a thick shell of a large stephanoceratid ammonite.

On a *Belemnopsis* sp. rostrum, there is a large (1 cm) *Calcideletrix flexuosa*, partly infilled with ferruginous material, partly with silica (Fig. 10 E). Main branches are c. 100 µm wide, but widened and flattened at the main bifurcations, distal branches are 50 µm, locally spiny. Anastomosis is infrequent, restricted to the centre of the trace. Branches are straight, apart from a few that are curved. This trace is superimposed by an extensive system of tunnels of *Orthogonum giganteum*.

One to several *Calcideletrix flexuosa* are located anywhere on the inner as well as on the outer sides of the shells, rarely on both sides; one shell of *Neocrassina obliqua* accommodates eight *C. flexuosa* borings on its outer side (Fig. 10 F). The diameter of the dentritic boring varies from 0.9-10 mm, with a medium size of 5.1 mm. The diameter of the branches is frequently 70-80 µm; it may reach 100 µm near the centre (one measures 130 µm) and decreases down to 60 µm in the peripheral branches. Branches are almost straight. As underlined by Wisshak (2017: 38) “Branches ramify in such a way as to cover the space between the branches almost equally”. This character is obvious in our material.

On a small valve of *Neocrassina obliqua*, a boring of *C. flexuosa* is apparently cut by an *Oichnus simplex* boring, which would mean that the settlement of *C. flexuosa* took place *syn-vivo*, assuming that the *Oichnus* injury was lethal. But this appearance is misleading since
a more careful examination shows that the branches of *C. flexuosa* go along the walls of the *O. simplex* boring. *C. flexuosa* thus settled (or developed) *post mortem*.

Several borings of *C. flexuosa* are covered by epibionts (tubes of *Glomerula gordialis*, oysters). More rarely, a specimen of *C. flexuosa* grows astride the edge of a shell.

The other bioerosion trace fossils in the shells that accommodate *C. flexuosa* are: *Trypanites* isp., *Oichnus simplex*, *Rogerella* isp., *Gastrochaenolites* isp.?!, *Talpina* isp., *Dictyoporus nodosus* (very common) and *Orthogonum giganteum*.

*Dictyoporus nodosus* Mägdefrau, 1937

The borings are located on bivalve shells (*Astarte elegans*, *Neocrassina obliqua*), stephanoceratid and oppeliid ammonites, pleurotomariid gastropods, and a *Belemnopsis* sp. rostrum. The size of this bioerosional trace is 7-35 mm (average value 18 mm). Galleries always develop as open channels with a mean size of 80 µm in diameter, but when a silicified internal mould of a tunnel is available, it shows a circular section and a diameter smaller than the surrounding channels, the width of which can reach 200 µm by taphonomic enlargement. The degree of anastomosis and the size of the mesh are variable. Sometimes, two *Dictyoporus nodosus* overlap and the trace becomes illegible. In a similar way, the overlapping of several traces of *Orthogonum giganteum* may be very misleading since they can look like an ill-preserved *Dictyoporus nodosus*.

*Nododendrina europaea* (Fischer, 1875)

Figure 11 A-I

A single *Belemnopsis* sp. rostrum accommodates eleven complete *N. europaea* and several incomplete specimens. A parabolic pit, 80-200 µm in diameter (average value 125 µm) is filled with silica and/or iron oxides, forming a spherical node *sensu* Wisshak (2017: 53-54) or chamber *sensu* Plewes et al. (1993: 86). The empty pits, which are numerous in this rostrum are 60-200 µm in diameter (average value 145 µm). The node gives issue to a single, fan-shaped, bushy plexus of branching, anastomosing galleries, irregular in diameter. The plexus is roughly triangular or rounded, or irregular. The angle of divergence of the plexus varies from 90-180° (mean value 140°). The overall dimensions, from the node to the furthest
ends of the galleries is 350-800 µm (540 µm in average). The diameter of the branches varies from 12-40 µm (mean value 25 µm).

Empty pits (i.e., devoid of node and plexus) can be seen in an internal layer of the rostrum, c. 0.2 mm under the surface of the rostrum, on which one can find the same pits. This indicates two episodes of infestation, among which the first one took place *syn-vivo*.

**Remarks.** *Nododendrina europaea* is frequently encountered in shells and other carbonate substrates from the Carboniferous to Recent (Bromley et al., 2007). For instance, Bernard-Dumanois & Delance (1983: 422, fig. 4 A, pl. I-1), Mayoral (1988a: 105, fig. 2.1, pl. II-1), Cherchi & Schröder (1991: 112-115, fig. 1-6) have illustrated this boring respectively from Bajocian, Pliocene and Recent, but without naming it. Plewes et al. (1993) described the boring from Upper Jurassic shells, under the name *Globodendrina monile* Plewes, Palmer & Haynes, 1993, as a foraminifer body fossil. Taylor et al. (2013) illustrated groups and individual *Semidendrina pulchra* Bromley, Wisshak, Glaub & Botquelen 2007 (= *Nododendrina europaea*), all at the same developmental stage in Early Cretaceous belemnite guards. Bernard-Dumanois & Delance (1983: fig. 4 A), Mayoral (1988a: fig. 2.1) and Cherchi & Schröder (1991) showed different developmental stages of the boring. The bioerosional trace *Nododendrina europaea* present on our *Belemnopsis* sp. rostra also show a nearly complete sequence of developmental stages. Belaústegui et al. (2016: 86-88) introduced the new concept of ichnogeny to describe the consecutive "ichnogenetic stages...which are directly related with the development of a boring or burrowing behaviour". Among the examples quoted by Belaústegui et al. (2016), we mention Bromley & D'Alessandro (1984) "phases of growth (A to E) of *Entobia*" and *Lepeichnus giberti* Belaústegui et al., 2016, and add the Recent *Semidendrina pulchra* Bromley et al. 2007 (=*Nododendrina europaea* (Fischer, 1875). Our *Nododendrina europaea* series on a Bajocian *Belemnopsis* sp. rostrum provides another good example of ichnogeny.

When the pits are empty and devoid of a node and plexus, they can scarcely be distinguished under a stereomicroscope from the *Cyclopuncta girtyi* pits; however, the former are parabolic whereas the bases of the latter are rather flat. But the distinction may be uncertain. The question of the relationships between the two bioerosion traces is raised, but will certainly need epoxy resin casting and SEM examination techniques in a future study.
5.14. *Single circular to tear-shapes attachment bioerosion traces (76)*: Centrichnus Bromley & Martinell, 1991.

*Centrichnus cf. concentricus* Bromley & Martinell, 1991

Fig. 12 A

On the inner side of a *Ctenostreon hector* shell fragment, two attachment bioerosional traces (= Fixichnia de Gibert et al., 2004) can be seen under a low-angle light. Both are circular and show perfectly concentric but faint rings. They are 5.5 mm in diameter. One has a flat central part (Fig. 12 A, right), the other has a small irregular pit in the central part (Fig. 12 A, left). Our trace fits Bromley & Martinell's (1991) original diagnosis with two differences: (1) there are no crenulations either on the outline or on concentric rings (one of the original figures of Bromley & Martinell (1991, fig. 7 C, bottom right) shows a scar devoid of crenulations); (2) the "central rounded depression" is very small or lacking. From a strict ichnotaxonomical point of view, our trace is close to *Centrichnus concentricus*. But the putative producer of this trace, a verrucid barnacle according to Bromley & Martinell (1991), is certainly different. The morphological differences may support the introduction of a new ichnospecies but we prefer, while waiting for new material, to leave it in open nomenclature, which stresses the proximity of the two ichnotaxa.

5.15 *Incertae sedis*: Foggara foggara *igen. nov.*, *isp. nov.* (by G.B.)

Ichnogenus *Foggara* igen. nov.

Type ichnospecies. *Foggara foggara* isp. nov.

**Etymology.** The architecture of this perforation is similar to that of a foggara. In arid areas of Algeria, this water supply system consists of underground aqueducts with regularly spaced wells, often with well copings. The wells are used for maintenance, ventilation and sand extraction within the main tunnel (Remini et al., 2010 and unpublished personal observations, Timimoun (Algeria) c. 1971). Gender feminine in accordance with the gender of the Arabic name.

**Diagnosis.** A cylindrical, straight or slightly curved tunnel, circular in section, bored into a calcareous substrate, for instance a shell, parallel and close to the surface. The tunnel is linked to the surface by short, perpendicular apertural canals, thinner than the main tunnel. The apertures are round.
Ichnospecies *Foggara foggara* isp. nov.

Fig. 12 B-E

**Etymology.** Tautonymy of the generic name.

**Type material.** Holotype MHNLM 2018.3.22 (Fig. 12 B-E) in a bivalve shell.

**Type locality.** Gavrus, west of Caen (Calvados, Normandy, France). Material collected in a ploughed field, 12.10.2018.

**Type horizon.** Oolithe ferrugineuse de Bayeux Formation, Bajocian.

**Diagnosis.** As for the genus.

**Description.** The substrate is a 2.7 mm-thick, silicified bivalve shell. The main tunnel is cylindrical and curved; its silicified infilling is 0.8 mm in diameter and its course runs for 25 mm between the sides of the broken shell. Fourteen apertures connect the main tunnel to the surface by a short apertural canal, 0.4 mm long at one end of the main tunnel and estimated 0.6-0.8 mm at the other end (Fig 12 E). The apertures are round, 0.2 mm in diameter. The apertures are spaced at irregularly intervals of 1.0-6.7 mm, with a mean value of 2 mm.

**Remarks.** Apertures, apertural canals and the main tunnel are reminiscent of the architecture of the “phase A” entobian borings. But the exploratory threads are usually branched with few apertures and not so perfectly cylindrical than the main tunnel of *Foggara foggara*. The sizes of the apertural canals are consistent with the sizes of the zooidal chambers of some boring bryozoans, e.g. the ichnogenus *Iramena* as described by Boekschoten (1970) in oyster shells and Wisshak et al. (2017) in a belemnite rostrum, but the stolons of the boring bryozoans are always ramified and their zooidal chambers are not regularly aligned along the stolons; see for instance, regardless of their status (body or trace fossils), the figures of the genera/ichnogenera *Pennatichnus*, *Pinaceocladichnus*, *Iramena* (Mayoral, 1988b), *Spathipora*, *Terebripora* (Fischer & Aguila, 2001). Similarly, the tunnels of *Talpina* ispp. are smaller in diameter and branched (Voigt, 1975; Wisshak et al. 2017). We have no satisfactory proposal for placing this ichnofossil within the categories of architectural design of Buatois et al. (2017), nor any hypothesis about the identity of the trace-maker.
**6. Discussion.**

We must stress again that the studied fossils were collected from ploughed fields, all being Bajocian in age and nearly all from the OFB Fm. Our conclusions may therefore reflect the diversity or the evolution of the palaeoenvironmental, sedimentological and taphonomical conditions in Normandy throughout the Bajocian. Moreover, most of the fossils are resedimented and/or re-elaborated (Pavia et al., 2013, 2015), which complicates the understanding of the individual histories of the trace-bearing shells and their encrusters and borers.

**6.1. *Ichnodiversity vs ichnodisparity.***

Table 1 shows that our 28 described bioerosional ichnotaxa fall within 14 of the categories of architectural design defined by Buatois et al. (2017). Both ichnodiversity and ichnodisparity are high. That probably signifies: (1) a generalized exploitation of the shells as calcareous substrates throughout the OFB Fm.; and (2) high diversity of the ecological contexts within the highly condensed OFB Fm., and constant reworking (resedimentation, re-elaboration) of the shells.

**6.2. *When did the encrusters and the borers settle on the shells?***

Very thick shells such as *Ctenostreon hector* were epibenthic elements. They played the role of hard calcareous substrates during their life: a large majority of the skeletobionts are located on the outer side of the valve. The inner sides of the valves are far less heavily exploited, necessarily post-mortem, after reworking of the isolated, even broken, valves. The same scheme applies to the pleurotomariid and other gastropod (pseudomelaniid) shells, though they seem on average to be less heavily encrusted or bored.

Bivalves with moderately thick valves (astartids, among which *Neocrassina obliqua* is the most frequent in the studied material) were endobenthic elements. The settlement of episkeletobionts was thus not possible *syn-vivo*. This is confirmed by the presence of encrusters, bioeroders and borers on both sides of the valves, with colonization taking place *post-mortem*. The belemnite guards are thought to fall in the same colonization scheme, with the only reliable colonization *syn-vivo* being provided by *Nododendrina europaea*.
The thin-shelled molluscs (other bivalves, ammonites, nautilids) and brachiopods host fewer borers, a fact that is obviously linked to the limitation of availablespace for boring into the thin shells rather than to their taphonomic history which they share with the other molluscs.

### 6.3. *Trophic groups of the epi- and endoskeletobionts.*

Epibionts and macroscopic boring and bioerosional trace-makers are suspension feeders (Table. 2). Grazers and predators are very few. The organisms responsible for microperforations are more diverse: suspension feeders, deposit feeders/decomposers and only one questionable case of a photosynthetic autotroph. This distribution of trophic groups compares well with the endolithic biota from the Speeton Clay Formation described by Taylor et al. (2013), or with the Upper Cenomanian oysters described by Breton (2017). In all cases, the number of boring taxa is greater than the number of encrusting taxa.

Table 3 shows the distribution of the confirmed ichnogenera of boring and bioerosional traces among the three sites. Some missing taxa are explicable by extrinsic causes (see the legend of the table), but otherwise the assemblage of ichnogenera bioeroding the shells and other organic substrates is typical of Mesozoic hard substrates in accordance with Taylor et al. (2013: 242).

### 6.4. *Palaeoenvironmental reconstruction.*

Among the boring and bioeroding ichnotaxa, the microendoliths are the best palaeobathymetric indicators (Glaub, 1994, 1999; Glaub et al., 2007; Vogel et al., 1995; Wisshak, 2012). Only one significant microboring was found in our material, which was identified questionably as *Ichnoreticulina* isp. It would denote the deep euphotic zone (Glaub, 1994, 1999; Glaub et al., 2007). Glaub (1994) stated, from her SEM study of vacuum cast-embedded microborings, that the OFB Fm. at Sainte-Honorine-des-Pertes (Calvados) was deposited in the deep euphotic zone. Compared to the SEM examination of vacuum cast-embedded specimens, the examination of natural SiO₂ casts underestimates the thinnest borings, which are the most characteristic for the euphotic zone. Dugué et al. (1998: 41) stated that “The depositional environment of the Oolithe Ferrugineuse de Bayeux was located in the photic zone, far from the coast line...”. Glaub’s (1994) conclusions and our observations
support the conclusion of Dugué et al. (1998) that: the OFB Fm. was deposited in the deep
euphotic zone.

6.5. *Contrasting ichnofacies.*

Though the discrete distribution of the shells, a shell ground constitutes a continuous
substrate for the skeletobiont colonization (Gibert et al., 2007) and is thus suitable for the
definition of an ichnofacies. Bromley & Asgaard (1993) proposed replacement of the
*Trypanites* ichnofacies, which was considered too large a concept (borings associated with
lithic hard substrate), with two ichnofacies, *Gnathichnus* and *Entobia* ichnofacies (see also
Gibert et al., 2007).

The main ichnogenera encountered in the OFB Fm. from Gavrus are
*Gastrochaenolites, Maeandropolydora, Teredolites*. *Entobia* is less frequent. All are deep-tier
endogenic traces with a dominance of Domichnia, which is characteristic of the *Entobia*
ichnofacies (Gibert et al., 2007).

According to Gibert et al. (2007), the colonization window is long, energy is high, and
the palaeoenvironment comprises: rocky shores (gravel beaches). This is obviously
inconsistent with palaeobathymetrical data, as deduced from the microborings (Glaub, 1994),
and sedimentological and palaeogeographical data. The OFB Fm. is not a shore deposit. The
complete lack of Pascichnia (*Radulichnus, Gnathichnus*) falsifies a hypothesis of alternating
*Gnathichnus* and *Entobia* ichnofacies throughout the OFB Fm.

Thus, the *Entobia* ichnofacies may be found in deeper, lower-energy environments, on
deep shell-grounds far from the coast. Therefore, the phases of reworking of the shells may
constitute high-energy episodes.

**7. Conclusion**

The vacuum cast-embedment with an epoxy resin is the most approved study method
of fossil microborings under a SEM (Wisshak, 2012), together with micro-CT, non-
destructive micro-computed tomography (Wisshak et al., 2017). The study of natural casts,
when available, is a good additional method. Our work shows that naturally silicified borings,
after HCl processing, can be studied under an optical stereomicroscope. A number of
ichnotaxa were revealed both by this method and by the cast-embedding technique applied by Glaub (1994) to similar OFB Fm. shells; the latter bringing to light a greater number of smaller microborings. In a further example, Hannon & Meyer (2014) compared Mississippian microendolithic structures both as naturally occurring internal moulds (in the voids of a naturally decalcified fossiliferous green shale) and epoxy casts examined under a SEM.

The two methods are complementary and when applied together enhance our knowledge and understanding of bioeroding organisms.

Declaration of links of interest

The authors declare that they have no links of interest.

Acknowledgements

We want to convey our warm thanks to all those who helped us with bibliography, documentation, identification, work on the field, equipment loan: Marc Chesnier (Caen), Dr Chis Clayton (Southampton), Dr Franz Fürsich (Erlangen), Benoît Hérisson (Le Havre), Nicolas Morel (Le Mans), association Port Vivant (Le Havre), Patrice Rabœuf (Le Mans), Jean-Philippe Rioult (Caen), Michel Rioult (Caen), Simon Schneider (Cambridge). Our special thanks to Dr Max Wisshak (Senckenberg am Meer) who permanently supported this work and taught me (GB) the ichnologic orthodoxy. TK is indebted to Jan Sklenář (National Museum at Prague) for free access for photographing process. GB thanks the Association Port Vivant (Le Havre) for documentation and loan of material. This research was financially supported by the Ministry of Culture of the Czech Republic (IP DKRVO 2019/2.III, National Museum, 00023272).

The three authors warmly thank the editor who encouraged this project, and the reviewers who allowed a noticeable improvement of the manuscript.

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## Figure captions

Figure 1. Thin section in a fragment of a *Ctenostreon hector* (d'Orbigny, 1850) shell (MHNLM 2018.3.67). Left: bright field, right: polarized illumination. a: crust of calcite cauliflower-like micro-concretions, b: silicified external layer, c, d: calcitic part of the shell, d: the original lamellar structure is preserved. Arrowhead: sphaero-radiolitic growth of calcedonite.

*Lame mince dans un fragment de coquille de Ctenostreon hector (d'Orbigny, 1850) (MHNLM 2018.3.67).* A gauche : lumière naturelle, à droite, lumière polarisée (nicols croisés). a : croûte de microconcrétions calcitiques en chou-fleur. b : couche externe silicifiée. c, d : partie de la coquille restée calcitique. d : partie où la structure lamellaire originale est préservée. Flèche : calcédonite sphéro-radiée.

Figure 2. A. *Belemnopsis* sp. rostrum, transversal section. (MHNLM 2018.3.81). B, C. *Obornella granulata* (Sowerby 1818). (MHNLM 2018.3.104). C is a close-up of the loose mesh (“cloisonné”) structure of the silica. D. *Acanthothyris spinosa* (Linnaeus, 1788) (MHNLM 2018.3.35), preservation of the spines. E. Beekite developed on the shell of a bivalve (*Plicatula* sp. ?) (MHNLM 2018.3.82). F. Stephanoceratidae (MHNLM 2018.3.84) with step-like silicified infillings of successive chambers. G. *Parkinsonia* sp. chambers (MHNLM 2018.3.83). A. Septa transformed in microcrystalline chalcedonite, B. Fibrous chalcedonite ending with small quartz crystals (C). D. Automorphic transparent quartz crystals.

A. *Rostre de Belemnopsis sp.*, coupe transversale. (MHNLM 2018.3.81). B, C. *Obornella granulata* (Sowerby 1818). (MHNLM 2018.3.104). C montre le détail de la structure en mailles lâches, en « cloisonné » de la silice. D. *Acanthothyris spinosa* (Linnaeus, 1788) (MHNLM 2018.3.35), préservation des épines. E. Beekite développée sur une coquille de bivalve *Plicatula* sp. ? (MHNLM 2018.3.82). F. Stephanoceratidae (MHNLM 2018.3.84) avec les remplissages sédimentaires silicifiés des loges successives en marches d'escalier. G. *Parkinsonia* sp., loges (MHNLM 2018.3.83). A. Cloison transformée en calcédonite
microcristalline. B. Calcédonite fibreuse se terminant par de petits cristaux de quartz (C). D. Gros cristaux automorphes de quartz transparent.

Figure 3. A. cf. *Sphenorhynchia plicatella* (Sowerby, 1825) (MHNLM 2018.3.69). From left to right: ventral view (the “roof” seen from above); side view, dorsal view. The red arrow shows the upper side of the thin “roof”, the white arrow its lower side. B. *Lamelliphorus ornatissimus* (d'Orbigny, 1850) (MHNLM 2018.3.85). C. *Astarte elegans* (Sowerby, 1816), *Spiroceras orbignyi* (Baugier & Sauzé, 1843), base of polychaetes tubes, dendrinid (arrow) and other perforations (MHNLM 2018.3.86). D. *Neuropora spinosa* (Lamouroux, 1821) [= *Acanthopora lamourouxi* Haime, 1854], (MHNLM 2018.3.70) and an astartid shell. E. Detail view of a branch of the sponge *Neuropora spinosa*. F. An encrusting, not branched, specimen of *Neuropora spinosa* on a pleurotomariid (MHNLM 2018.3.71). G. Large discoid hexactinellid (?) and its branched fixation surface (MHNLM 2018.3.72).

A. cf. Sphenorhynchia plicatella (Sowerby, 1825) (MHNLM 2018.3.69). De gauche à droite : vue ventrale (le « plafond » vu par-dessus) ; vue latérale ; vue dorsale. La flèche rouge désigne la face supérieure du mince « plafond », la flèche blanche sa face inférieure. B. Lamelliphorus ornatissimus (d'Orbigny, 1850) (MHNLM 2018.3.85). C. Astarte elegans (Sowerby, 1816), Spiroceras orbignyi (Baugier & Sauzé, 1843), bases de tubes de polychètes, Dendrinidae (flèche) et autres perforations (MHNLM 2018.3.86). D. Neuropora spinosa (Lamouroux, 1821) [= Acanthopora lamourouxi Haime, 1854], (MHNLM 2018.3.70) et une coquille d'Astartidae. E. Détail d'un rameau du spongiaire Neuropora spinosa. F. Spécimen non ramifié de Neuropora spinosa encroûtant une coquille de Pleurotomariidae (MHNLM 2018.3.71). G. Grande hexactinellide discoïde et sa surface de fixation ramifiée (MHNLM 2018.3.72).

Figure 4. Bajocian sabellids (A-D) and serpulids (E-N). A-D. *Glomerula gordialis* (von Schlotheim, 1820). A-C. Tube fragments, entirely isolated from their matrix by means of hydrochloric acid. D. Tube attached to the inner surface of a single valve of the bivalve *Trigonia elongata* J. de C. Sowerby, 1823. (A, B: MHNLM 2018.3.61; C, D: MHNLM 2018.3.59). E-F. *Metavermilia* sp. E. Tube fragment attached to a bivalve (MHNLM 2018.3.52). F. Two damaged tubes and bases of several more but destroyed tubes attached to
a shell fragment of a bivalve (MHNLM 2018.3.51). G-I. *Cementula* sp. 1. G. A damaged tube consisting of several spirals, entirely isolated from its substrate and matrix by means of hydrochloric acid. H. Several (at least two) spiral tubes together with a tube of *Propomatoceros lumbricalis* forma "limax" (in lower half of the cutting) attached to the inner surface of a single valve of the bivalve *Ctenostreon hector* (d'Orbigny, 1850). I. A small spiral attached to a shell fragment (MHNLM 2018.3.55). J-K. *Cementula* sp. 2 (MHNLM 2018.3.57). Two spirals and several more tube fragments, attached to opposite surfaces of a shell fragment of the gastropod *Pleurotomaria armata* Münster in Goldfuss, 1844. L-N. *Propomatoceros lumbricalis* (von Schlotheim, 1820) forma "limax" (Goldfuss, 1831). L. Tube fragment with aperture, attached to a heavily worn, presumably reworked steinkern of an undetermined small ammonite (MHNLM 2018.3.44). M. Tube fragment attached to a well-preserved shell of a gastropod of the family Pleurotomariidae (MHNLM 2018.3.42). M1. detail, showing oblique lateral/frontal view to aperture. N. Tube attached to the inner surface of a single bivalve shell, aperture preserved, posterior tube portion damaged (MHNLM 2018.3.50) (Photographs and preparation of figure 4 by TC).

Sabellidae (A-D) et *Serpulidae* (E-N) bajociens. A-D. Glomerula gordialis (von Schlotheim, 1820). A-C. Fragments de tubes entièrement isolés de leur matrice après action de l'acide chlorhydrique. D. Tube fixé à la face d'une valve isolée du bivalve Trigonia elongata J. de C. Sowerby, 1823. (A, B: MHNLM 2018.3.61; C, D: MHNLM 2018.3.59). E-F Metavermilia sp. E. Fragment de tube fixé sur un bivalve (MHNLM 2018.3.52). F. Deux tubes endommagés avec les bases de quelques autres fixés sur un fragment de coquille de bivalve (MHNLM 2018.3.51). G-I. *Cementula* sp. 1 (MHNLM 2018.3.45). G. Un tube endommagé formé de quelques spires, entièrement isolé de son substrat et de sa matrice par l'action de l'acide chlorhydrique. H. Quelques (au moins deux) tubes spiralés et un tube de *Propomatoceros lumbricalis* forma "limax" (partie inférieure de l'image) fixés sur la surface interne d'une valve isolée du bivalve *Ctenostreon hector* (d'Orbigny, 1850). I. Petit tube spiralé fixé à un fragment de coquille. J-K. *Cementula* sp. 2 (MHNLM 2018.3.55). Deux tubes spiralés et quelques autres fixés sur des faces opposées d'un fragment de la coquille du gastropode *Pleurotomaria armata* Münster in Goldfuss, 1844. L-N. *Propomatoceros lumbricalis* (von Schlotheim, 1820) forma "limax" (Goldfuss, 1831). L. Fragment de tube avec son ouverture, fixé sur le moule interne d'une ammonite indéterminée, très mal conservée, probablement remaniée (MHNLM 2018.3.44). M. Fragment de tube fixé à la coquille bien conservée d'un gastropode Pleurotomariidae (MHNLM 2018.3.42). M1. Détail, montrant une vue latérale/frontale oblique de l'ouverture. N. Tube fixé à la face interne d'une coquille de
bivalve, ouverture conservée, partie postérieure du tube endommagée (MHNLM 2018.3.50)
(photos et préparation de la figure 4 par TC).

Figure 5. Bajocian serpulids. A. Serpulidae, gen. et sp. indet. This term refers to the many small tubes, attached to a sponge. The damaged coiled base in the centre represents a different, larger indeterminable tube which may have been a *Propomatoceras lumbricalis* or a *Mucroserpula* sp. (MHNLM 2018.3.64). B-C. *Mucroserpula* sp. 1 or *Pyrgopolon (Septenaria)* sp.? B. Nearly complete free tube portion, broken off at the transition from attached to free portion, showing frontal view to posterior cross-section and oblique view to upper side (MHNLM 2018.3.46). B1. Underside. B2. Slightly oblique view to upper side and part of latus, showing keels protruding as damaged spines at the aperture. B3. Frontal view to damaged aperture. C. Anterior fragment of posterior tube portion attached to a fragment of a bivalve shell and steeply rising complete free anterior tube portion, oblique view to aperture and upper side of the free tube portion (MHNLM 2018.3.54). C1. Oblique view to aperture and underside of the free tube portion showing five keels ending as protruding spines at the aperture and base formed by protruding latera enclosing a small basal "cave". C2. Upper side of attached and free tube portions, aperture on the left. C3. Lateral view to attached and steeply rising free tube portions showing base with "cave" and protruding spines at aperture. D. *Nogrobs vermicularis* de Montfort, 1808, lateral view (MHNLM 2018.3.47). D1. Aperture or cross-section. E. *Mucroserpula cf. tricarinata* (J. de C. Sowerby, 1829), upper side of a damaged tube, together with a small spiral tube of *Cementula* sp. 1 and a curved undetermined serpulid tube attached to a shell fragment (MHNLM 2018.3.78). F-G. *Mucroserpula* sp. 2 (MHNLM 2018.3.55). F. S-shaped tube, upper side, attached beside a small spiral tube of *Cementula* sp. 1 which is also shown in Fig. 4 I, on a fragment of a bivalve shell. G. Curved anterior fragment with aperture, oblique frontal view to aperture / lateral view, attached to a shell fragment. G1. Frontal view showing outline of aperture. G2. Upper side (Photographs and preparation of figure 5 by TC).

*Serpulidae bajociens*. A. Serpulidae, gen. et sp. indet. Cette identification se rapporte aux nombreux petits tubes fixés sur une éponge. La base de tube enroulée, endommagée dans le centre de l'image représente une espèce plus grande, indéterminable, mais qui peut avoir été un *Propomatoceras lumbricalis* ou un *Mucroserpula* sp. (MHNLM 2018.3.64). B-C. *Mucroserpula* sp. 1 or *Pyrgopolon (Septenaria)* sp.? B. Portion de tube libre, presque
complète, cassée à la limite entre la partie fixée et la partie libre, montrant une vue frontale de la section postérieure, et une vue oblique de la partie supérieure (MHNLM 2018.3.46). B1. Partie inférieure. B2. Vue légèrement oblique de la partie supérieure et en partie des côtés, montrant les crêtes sous la forme d'épines endommagées dépassant dans l'ouverture. B3. Vue frontale de l'ouverture endommagée. C. Fragment antérieur de la partie postérieure du tube fixée sur un fragment de coquille de bivalve et sa partie antérieure complètement libre s'élevant de manière abrupte, vue oblique de l'ouverture et partie supérieure de la partie libre du tube (MHNLM 2018.3.46). C1. Vue oblique de l'ouverture et de la partie inférieure de la portion libre du tube montrant quatre crêtes se terminant en épines dépassant à l'ouverture et la base formée par des latera entourant une petite cavité basale. C2. Face supérieure des parties fixée et libre du tube, ouverture à gauche. C3. Vue latérale des parties fixée et libre, s'élevant de manière abrupte, montrant la base avec la cavité et les épines dépassant à l'ouverture. D. Nogrobs vermicularis de Montfort, 1808, vue latérale (MHNLM 2018.3.47). D1. Ouverture ou section transversale. E. Mucroserpula cf. tricarinata (J. de C. Sowerby, 1829), face supérieure d'un tube endommagé, avec un petit tube spiralé de Cementula sp. 1 et un tube indéterminé de Serpulidae fixé sur un fragment de coquille (MHNLM 2018.3.78). F-G. Mucroserpula sp. 2 (MHNLM 2018.3.55). F. Tube sigmoïde, face supérieure, fixé à côté d'un petit tube spiralé de Cementula sp. 1 qui est aussi représenté Fig. 4 I, sur un fragment de coquille de bivalve. G. Partie antérieure courbe avec l'ouverture, vue frontale oblique de l'ouverture / vue latérale, fixée sur un fragment de coquille. G1. Vue frontale montrant le contour de l'ouverture. G2. Face supérieure (photos et préparation de la figure 5 par TC).

Figure 6. A. *Stomatopora* cf. *dichotomoides* (d'Orbigny, 1850), (MHNLM 2018.3.77), on a *Belemnopsis* sp. rostrum. B. cf. *Reptomultisparsa cricopora* (Vine, 1881), (MHNLM 2018.3.76B) on the same *Belemnopsis* sp. rostrum. C. Group of more than a dozen of attached valves of *Moorellina* (Elliottina) dubia (d'Orbigny, 1850) on the inner side of a valve of *Astarte elegans* Sowerby, 1816. (MHNLM 2018.3.27). D. Close-up of the attached valve of *Moorellina* (Elliottina) dubia on a *Belemnopsis* sp. rostrum, (MHNLM 2018.3.76A). E. Ostreidae, LV (MHNLM 2018.3.87), from left to right: internal view with the adductor muscle scar, view from the attachment side, ventral view. Arrows : *Oichnus simplex* Bromley, 1981. F. *Lopha ? hastellata* (von Schlotheim, 1820), (MHNLM 2018.3.74), incomplete RV showing an axial xenomorphic sculpture of a cylindrical, supposed initially vertical support
on which the LV was fixed (between the two arrows). G. *Lopha ? hastellata* LV with several species of oysters attached on the inner side (MHNLM 2018.3.73). H. *Cosmetodon hirsonensis* (d'Archiac, 1843), two valves preserved in the hollow of a belemnite phragmocone (MHNLM 2018.3.75).

A. Stomatopora cf. dichotomoides (d'Orbigny, 1850) (MHNLM 2018.3.77), sur un rostre de Belemnopsis sp. B. cf. Reptomultisparsa cricopora (Vine, 1881), (MHNLM 2018.3.76B) sur un rostre de Belemnopsis sp. C. Groupe d'au moins une douzaine de valves fixées de Moorellina (Elliottina) dubia (d'Orbigny, 1850) sur la face interne d'une valve d'Astarte elegans Sowerby, 1816. (MHNLM 2018.3.27). D. Détail d'une valve fixée de Moorellina (Elliottina) dubia sur un rostre de Belemnopsis sp., (MHNLM 2018.3.76A). E. Ostreidae (MHNLM 2018.3.87), VG, de gauche à droite : vue interne avec l'empreinte du muscle adducteur, vue de la surface de fixation, vue ventrale. Flèches : Oichnus simplex Bromley, 1981. F. Lopha ? hastellata (von Schlotheim, 1820), (MHNLM 2018.3.74), VD incomplète montrant la sculpture xénomorphe d'un support cylindrique, supposé vertical à l'origine, sur lequel la VG était fixée (entre les deux flèches). G. Lopha ? hastellata VG avec plusieurs espèces d'huitres fixées sur la face interne (MHNLM 2018.3.73). H. Cosmetodon hirsonensis (d'Archiac, 1843) (MHNLM 2018.3.75), deux valves en connexion conservées dans le creux d'un phragmocône de bélemnite.

Figure 7. A. *Arachnostega* isp. cf. A. *gastrochaenae* Bertling, 1992 (MHNLM 2018.3.79), partly silicified internal cast, developed inside a pleurotomariid. B. *Cyclopuncta girtyi* Elias, 1958 (MHNLM 2018.3.19), dense group of pits on the inner side of a *Ctenostreon hector* shell. C. *Cyclopuncta girtyi* (MHNLM 2018.3.80), group of pits on the outer side of a *Ctenostreon hector* shell (detail). Note the figure-of-eight opening of a *Gastrochaenolites dijugus* Kelly & Bromley, 1984 (upper left). D, E. *Planavolites wisshaki* isp. nov., holotype (MHNLM 2018.3.32) on the outer side of a *Neocrassina obliqua* shell. D. Overview, E. Detail. F. *Planavolites wisshaki* isp. nov., type-series. Holotype : H. Paratypes: P1 (MHNLM 2018.3.15); P2 (MHNLM 2018.3.36); P3(MHNLM 2018.3.34). Camera lucida drawings.

A. *Arachnostega* isp. cf. A. *gastrochaenae* Bertling, 1992 (MHNLM 2018.3.79), moule interne partiellement silicifié, développé à l'intérieur d'une coquille de Pleurotomariidae. B. *Cyclopuncta girtyi* Elias, 1958 (MHNLM 2018.3.19), groupe dense de trous développé sur la face interne d'une coquille de *Ctenostreon hector*. C. *Cyclopuncta girtyi* (MHNLM 2018.3.80),
groupe de trous sur la face externe d'une coquille de Ctenostreon hector (détail). Noter
l'ouverture en 8 d'un Gastrochaenolites dijugus Kelly & Bromley, 1984 (en haut à gauche).
D, E. Planavolites wisshaki isp. nov., holotype (MHNLM 2018.3.32) sur la face externe d'une
coquille de Neocrassina obliqua. D. Vue d'ensemble, E. Détail. F. Planavolites wisshaki isp.
nov., série-type. Holotype : H. Paratypes: P1 (MHNLM 2018.3.15); P2 (MHNLM 2018.3.36);
P3(MHNLM 2018.3.34), dessins faits au tube à dessiner.

Figure 8. A. *Oichnus simplex* Bromley, 1981 (arrow) (MHNLM 2018.3.18) in *Obornella granulata* (Sowerby, 1818). B. A healed wound (MHNLM 2018.3.26) (arrowhead) in *Obornella granulata*. The two shells (Fig. 8 A and B) are oriented parallel each other, in order to show that the wound or the perforation are located at the same place on the pleurotomariid shell. C. *Rogerella elliptica* (Codez & de Saint-Seine, 1958) (MHNLM 2018.3.89) located preferentially in the ridge of the ribs of a *Ctenostreon hector* shell. D. *Rogerella mathieui* de Saint-Seine, 1955 (MHNLM 2018.3.40) in *Pseudomelania lineata* (Sowerby, 1818). E-G. *Gastrochaenolites dijugus* Kelly & Bromley, 1984 in a *Ctenostreon hector* shell. E. Apertures figure-of-eight shaped (arrow) and *Lithophaga fabella* (Eudes-Deslongchamps, 1838) valves preserved in a perforation (arrowhead) (MHNLM 2018.3.80) [same specimen as Fig. 7C]. F. *Lithophaga fabella* preserved in perforations (MHNLM 2018.3.90), intermediate step in the HCl process; the valves of the bivalve have been damaged during later steps. G. Longitudinal section of a boring (MHNLM 2018.3.91). H. *Talpina* isp, tunnels and openings on the inner side of the shell of a *Ctenostreon hector* (MHNLM 2018.3.39). I. *Orthogonum giganteum* Glaub, 1994 (MHNLM 2018.3.13) in a *Belemnopsis* sp. rostrum. J. *Orthogonum* isp. within a thick *Ctenostreon hector* shell, several millimetres under the surface of the shell. K, L. *Orthogonum giganteum* Glaub, 1994 (MHNLM 2018.3.14) in a *Belemnopsis* sp. rostrum: two zones on the same rostrum.

A. Oichnus simplex Bromley, 1981 (flèche) (MHNLM 2018.3.18) sur Obornella granulata (Sowerby, 1818). B. Une blessure cicatrisée (MHNLM 2018.3.26) (pointe de flèche) sur Obornella granulata. Les deux coquilles (Fig. 8 A and B) sont orientées parallèlement afin de mettre en évidence la position identique de la blessure et de la perforation sur les deux coquilles. C. Rogerella elliptica (Codez & de Saint-Seine, 1958) (MHNLM 2018.3.89) situées préférentiellement sur les côtes d'une coquille de Ctenostreon hector. D. Rogerella mathieui de Saint-Seine, 1955 (MHNLM 2018.3.40) sur Pseudomelania lineata (Sowerby, 1818). E-G.
Gastrochaenolites dijugus Kelly & Bromley, 1984 sur des coquilles de Ctenostreon hector. E. Ouvertures en 8 (flèche) et Lithophaga fabella (Eudes-Deslongchamps, 1838), valves préservées dans une perforation (pointe de flèche) (MHNLM 2018.3.80), même spécimen que Fig. 7C. F. Lithophaga fabella préservées dans des perforations (MHNLM 2018.3.90), étape intermédiaire du traitement à l'acide chlorhydrique ; les valves du bivalve ont été endommagées lors de la poursuite du traitement. G. Coupe longitudinale d'une perforation (MHNLM 2018.3.91). H. Talpina isp, tunnels et ouvertures, face interne d'une coquille de Ctenostreon hector (MHNLM 2018.3.39). I. Orthogonum giganteum Glaub, 1994 (MHNLM 2018.3.13) sur un rostre de Belemnopsis sp. J. Orthogonum isp. dans l'épaisseur d'une coquille de Ctenostreon hector, quelques millimètres sous la surface de la coquille K, L. Orthogonum giganteum Glaub, 1994 (MHNLM 2018.3.14) sur un rostre de Belemnopsis sp. : deux zones sur le même rostre.

Figure 9. A. *Igen. isp.* A on *Sphenorhynchia plicatella* (Sowerby, 1825) (MHNLM 2018.3.94) Other borings include *Rogerella isp.* B, C. *Saccomorpha isp.* in *Ctenostreon hector* (MHNLM 2018.3.39). B. Undamaged group of pouches (working document). C. The same, after accidental destruction of the central pouches. Note the axial tunnel with a brown infilling. D-F. *Saccomorpha isp.* on *Pseudomelania lineata* (Sowerby, 1818) (MHNLM 2018.3.40). D. overall view of the main part of the group. The white frames delineate the parts which are enlarged in Fig. 9 E and 9 F. E, F. Detail views.

*Igen. isp.* A sur *Sphenorhynchia plicatella* (Sowerby, 1825) (MHNLM 2018.3.94) Les autres perforations comprennent *Rogerella isp.* B, C. *Saccomorpha isp.* sur *Ctenostreon hector* (MHNLM 2018.3.39). B. Groupe de poches intact (document de travail). C. Le même, après destruction accidentelle des poches centrales. Noter le tunnel axial à remplissage de couleur brune. D-F. *Saccomorpha isp.* sur *Pseudomelania lineata* (Sowerby, 1818) (MHNLM 2018.3.40). D. Vue d'ensemble de la partie principale du groupe. Les cadres blancs délimitent les parties agrandies Fig. 9 E et 9 F. E, F. Vues de détail.
Figure 10. A-C. *Kleithrichnus belemnophilus* igen. nov., isp. nov. A. Holotype (MHNLM 2018.3.7). On the right, the 3-D network is interrupted by a veinlet of partly silicified calcite. B. Paratype (MHNLM 2018.3.9). White arrowheads: main tunnels of the superficial tier. Red arrowhead: deeper tier of thinner tunnels. C. Paratype (MHNLM 2018.3.10). White arrowhead: main tunnels of the superficial tier. Red arrowhead: deeper tier of thinner tunnels. D. *Entobia geometrica* Bromley & D'Alessandro, 1984 (MHNLM 2018.3.21). Left: two-sized apertures on the inner side of a *Ctenostreon hector* shell. Right: walls of the chamber(s) with numerous thin intercameral canals openings. E. *Calcideletrix flexuosa* Mägdefrau, 1937 on a *Belemnopsis* rostrum (MHNLM 2018.3.13). The boring is partly infilled with ferruginous material, and partly (lower right) with white silica. Same rostrum as Fig. 8 I. F. Eight *Calcideletrix flexuosa* on the outer side of a *Neocrassina obliqua* shell (red arrowheads); the blue arrowheads show *Orthogonum giganteum* tunnels, and the green ones two *Oichnus simplex*. (MHNLM 2018.3.33).

A-C. Kleithrichnus belemnophilus igen. nov., isp. nov. A. Holotype (MHNLM 2018.3.7). Sur la partie droite de l'image, le réseau est interrompu par une petite veine de calcite partiellement silicifiée. B. Paratype (MHNLM 2018.3.9). Pointes de flèches blanches: Tunnels principaux superficiels. Pointe de flèche rouge: Tunnels plus fins et plus profonds. C. Paratype (MHNLM 2018.3.10). Pointe de flèche blanche: tunnels principaux superficiels. Pointe de flèche rouge: tunnels plus fins et plus profonds. D. Entobia geometrica Bromley & D'Alessandro, 1984 (MHNLM 2018.3.21). A gauche : ouvertures de deux tailles sur la face interne d'une coquille de *Ctenostreon hector*. A droite: paroi de la (ou des) chamber(s) avec de nombreuses ouvertures de fins canaux inter-chambres. E. Calcideletrix flexuosa Mägdefrau, 1937 sur un rostre de *Belemnopsis* (MHNLM 2018.3.13). La perforation est emplie pour partie de matière ferrugineuse, et pour partie (en bas à droite) de silice blanche. Même rostre que Fig. 8 I. F. Huit Calcideletrix flexuosa sur la face externe d'une coquille de *Neocrassina obliqua* (pointes de flèches rouges); les pointes de flèches bleues désignent des tunnels d'Orthogonum giganteum, et les vertes deux *Oichnus simplex* (MHNLM 2018.3.33).

Figure 11. *Nododendrina europaea* (Fischer, 1875) in a *Belemnopsis* sp. rostrum (MHNLM 2018.3.95). A-E. Ichnogenetic series from a specimen with a moderately developed plexus (A) to specimens with strongly developed plexus (E, F). D shows a plexus with silica (left) and ferruginous (right) infilling. E. Node is not preserved. C shows also an *Orthogonum*
giganteum filled with ferruginous material. No scale bar: all pictures at the same scale, 1 x 1 mm. G. Diagrammatic sketch of a typical, developed *Nododendrina europaea*. Ch: chamber, No: node, Pl: plexus. H. Group of five perforations. Green arrows: developed *N. europaea* with node and plexus, red arrows: initial stage of development, chambers alone. I. White arrow: node made of ferruginous material and silicified plexus. Red arrow: initial stage of development, chamber without node and plexus.

*Nododendrina europaea* (Fischer, 1875) sur un rostre de Belemnopsis sp. (MHNLM 2018.3.95). A-E. Série ichnogénétique depuis un spécimen avec un plexus peu développé (A) jusqu’à des spécimens avec des plexus très développés (E, F). D montre un plexus avec un remplissage ferrugineux à droite et siliceux à gauche. E. Node non préservé. C montre aussi un Orthogonum giganteum à remplissage ferrugineux. Pas de barre d’échelle, toutes les images représentent 1 x 1 mm. G. Croquis schématique d’un *Nododendrina europaea* développé. Ch: chambre, No: node, Pl: plexus. H. Groupe de cinq perforations. Flèches vertes: N. europaea développés avec node et plexus, flèches rouges: stade initial du développement, chambres seules. I. Flèche blanche : node ferrugineux et plexus silicifié. Flèche rouge: stade initial du développement, chambres sans node ni plexus.

Figure 12. A. *Centrichnus cf. concentricus* Bromley & Martinell, 1991 (MHNLM 2018.3.38). Low angle of incidence illumination. B-E. *Foggara foggara* igen. nov., isp. nov., holotype (MHNLM 2018.3.22), in a bivalve shell. Specimen processed with HCl. B. View from the inner side of the shell. The tunnel can be seen where the inner side of the shell is not preserved. C. Outer side of the shell, with fourteen apertures. D. Same view than C, but with a diascopic illumination showing the apertures exactly superimposed on the course of the tunnel. E. Enlargement of C.

A. *Centrichnus cf. concentricus* Bromley & Martinell, 1991 (MHNLM 2018.3.38). Eclairage rasant. B-E. Foggara foggara igen. nov., isp. nov., holotype (MHNLM 2018.3.22), sur une coquille de bivalve. Spécimen traité à l'acide chlorhydrique. B. Vue de la face interne de la coquille. Le tunnel est visible là où la face interne de la coquille n'est pas conservée. C. Face externe de la coquille, avec les quatorze ouvertures. D. Comme C, mais avec éclairage diascopique montrant la superposition exacte des ouvertures au trajet du tunnel. E. Agrandissement de C.
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<table><caption>Table 1: Borings and bioerosion traces of the OFB from Gavrus (Bajocian, Normandy, France)</caption><thead><tr><th></th><th>Category of<br>architectural<br>design (a)</th><th>Number of<br>ichnotaxa<br>or ichnotaxa</th><th>Assumed<br>trace-producer</th><th>Trophic group<br>of the<br>trace-producer</th><th>Bathymetric<br>implication</th></tr></thead><tbody><tr><td rowspan="14">Borings and bioerosion traces</td><td>16</td><td>1</td><td rowspan="3">Polychaetes</td><td>Deposit-feeder</td><td rowspan="14"></td></tr><tr><td>59</td><td>1</td><td>Suspension-<br>feeder</td></tr><tr><td>61</td><td>2</td><td>Deposit-<br>feeder,<br>decomposer</td></tr><tr><td rowspan="3">63</td><td><i>Cyclopuncta girtyi</i></td><td>Foraminiferan</td><td>Grazer ?</td></tr><tr><td><i>Planavolites<br>wisshaki</i></td><td>?</td><td>predator</td></tr><tr><td><i>Oichnus simplex</i></td><td>Gastropod</td><td>Suspension-<br>feeder</td></tr><tr><td>65</td><td>2</td><td>Acrothoracican<br>barnacle</td><td rowspan="2">Phototroph</td><td rowspan="2">Photic zone</td></tr><tr><td>66</td><td>3</td><td>Bivalvia</td></tr><tr><td rowspan="2">68</td><td><i>Talpina isp.</i></td><td>Phoronid</td><td rowspan="2">Heterotrophic<br>decomposers</td><td rowspan="2">Aphotic<br>zone</td></tr><tr><td><i>Ichnoreticulina isp.</i><br>?</td><td>Alga or<br>cyanobacteria</td></tr><tr><td>69</td><td>4</td><td rowspan="2">Fungus</td><td rowspan="2">?</td><td rowspan="2"></td></tr><tr><td>70</td><td>1</td></tr><tr><td>71</td><td>1</td><td>?</td><td>Suspension-<br>feeder</td><td rowspan="7"></td></tr><tr><td>72</td><td>2</td><td>Sponge</td><td>Deposit<br>feeder,<br>decomposer</td></tr><tr><td>75<br>Dendrinidae</td><td>3</td><td>Foraminiferan or<br>microsponge</td><td>?</td></tr><tr><td>76</td><td>1</td><td rowspan="2">?</td><td rowspan="2">?</td></tr><tr><td><i>Incertae sedis</i></td><td>1</td></tr><tr><td rowspan="2">Total</td><td>Ichnodisparity</td><td>Ichnodiversity</td><td></td><td></td></tr><tr><td>14 (b)</td><td>28 (b)</td><td></td><td></td></tr></tbody></table>

(a) Following the numbering of Buatois et al. (2017)

(b) Only the traces described in this paper are mentioned, the other microperforations described by Glaub (1994) are not.

Perforations et traces de bioérosion de l'OFB de Gavrus (Bajocien, Normandie, France)

(a) Selon la numérotation de Buatois et al. (2017)

(b) Seules les traces décrites dans cet article sont mentionnées, les autres microperforations décrites par Glaub (1994) ne le sont pas.
<table><caption>Table 2: Epizoans of the OFB from Gavrus (Bajocian, Normandy, France)</caption><thead><tr><th></th><th>Group</th><th>Number of taxa</th><th>Trophic group</th></tr></thead><tbody><tr><td rowspan="6">Epizoans</td><td>Porifera</td><td>4</td><td rowspan="6">Suspension feeders</td></tr><tr><td>Polychaetes</td><td>10</td></tr><tr><td>Bryozoans</td><td>n</td></tr><tr><td>Brachiopoda</td><td>n</td></tr><tr><td>Cemented bivalves</td><td>4</td></tr><tr><td>Other Bivalves</td><td>1</td></tr><tr><td>Number</td><td>6</td><td>&gt; 20</td><td></td></tr></tbody></table>

Epizoaires de l'OFB de Gavrus (Bajocien, Normandie, France)
<table><caption>Table 3. Distribution of the borings and bioerosion ichnogenera (in alphabetical order) among three Mesozoic sites: Gavrus, OFB Fm., Bajocian, any shell (this work); Yorkshire Speeton Clay Fm., Early Cretaceous, belemnite guards (Taylor et al., 2013); Le Mans, Marnes à Pycnodonte biauriculata Fm., Upper Cenomanian, oyster shells (Breton, 2017).</caption><thead><tr><th>Ichnogenera</th><th>Gavrus Bajocian OFB Any shell</th><th>Speeton Clay Early Cret. Belemnites</th><th>Le Mans U Cenomanian Oysters</th></tr></thead><tbody><tr><td>Calcideletrix</td><td>++</td><td></td><td>+</td></tr><tr><td>Caulostrepsis</td><td></td><td>+</td><td></td></tr><tr><td>Centrichnus</td><td>+</td><td></td><td></td></tr><tr><td>Cyclopuncta</td><td>+</td><td></td><td></td></tr><tr><td>Dictyoporus</td><td>++</td><td></td><td>+</td></tr><tr><td>Entobia</td><td>+</td><td>+</td><td>++</td></tr><tr><td>Foggara</td><td>+</td><td></td><td></td></tr><tr><td>Gastrochaenolites</td><td>++</td><td>+</td><td>++</td></tr><tr><td>Gnathichnus</td><td></td><td>+</td><td>++</td></tr><tr><td>Kleithrichnus</td><td>++</td><td></td><td></td></tr><tr><td>Loxolenichnus</td><td></td><td></td><td>+</td></tr><tr><td>Maeandropolydora</td><td>++</td><td>++</td><td>++</td></tr><tr><td>Nododendrina</td><td>+</td><td>++</td><td></td></tr><tr><td>Oichnus</td><td>+</td><td></td><td>++</td></tr><tr><td>Orthogonum</td><td>++</td><td>++</td><td></td></tr><tr><td>Planavolites</td><td>+</td><td></td><td></td></tr><tr><td>Podichnus</td><td></td><td>+</td><td>+</td></tr><tr><td>Radulichnus</td><td></td><td></td><td>+</td></tr><tr><td>Rhopalia</td><td></td><td>++</td><td></td></tr><tr><td>Rogerella</td><td>++</td><td>++</td><td>++</td></tr><tr><td>Saccomorpha</td><td>+</td><td>++</td><td></td></tr><tr><td>Sulcichnus?</td><td></td><td>+</td><td></td></tr><tr><td>Talpina</td><td>++</td><td></td><td>++</td></tr><tr><td>Trypanites</td><td>++</td><td></td><td>++</td></tr></tbody></table>

The lack of certain ichnogenera may be due to the used techniques of preparation. For instance, the Cenomanian oysters from Le Mans have not been processed with HCl because they are not silicified, and cannot thus display such ichnogenera as *Saccomorpha* or *Rhopalia*. The lack of *Oichnus* in Speeton Clay belemnites is obviously due to the absence of attack of a predatory gastropod on such a substrate. The shadowed cells correspond to significant lacks of the ichnogenus.

Répartition des ichnogenres de perforations et de traces de bioérosion (en ordre alphabétique) dans trois sites mésozoïques : Gavrus, Fm OFB, Bajocien, toutes coquilles (ce travail); Yorkshire, Fm des Argiles de Speeton, Crétacé inférieur, rostres de bélemnites (Taylor et al., 2013); Le Mans, Fm des Marnes à Pycnodonte biauriculata, Cénomanien supérieur, coquilles d'huitres (Breton, 2017).
L'absence de certains ichnogenres peut être due aux techniques utilisées pour la préparation. Par exemple, les huitres su Cénomanien du Mans n'ayant pas été traitées à l'acide chlorhydrique parce qu'elle ne sont pas silicifiées ne peuvent pas montrer des ichnogenres comme Saccomorpha ou Rhopalia. L'absence d'Oichnus sur les bélemmites des argiles de Speeton est évidemment due à l'absence d'attaque de gastropode prédateur sur de tels substrats. Les cellules grisées correspondent aux absences significatives des ichnogenres.