# An overview and brief description of common marine organic-walled dinoflagellate cyst taxa occurring in surface sediments of the Northern Hemisphere

Nicolas van Nieuwenhove, Martin J. Head, Audrey Limoges, Vera Pospelova, Kenneth Mertens, Jens Matthiessen, Stijn de Schepper, Anne de Vernal, Frédérique Eynaud, Laurent Londeix, et al.

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## ► To cite this version:

Nicolas van Nieuwenhove, Martin J. Head, Audrey Limoges, Vera Pospelova, Kenneth Mertens, et al. An overview and brief description of common marine organic-walled dinoflagellate cyst taxa occurring in surface sediments of the Northern Hemisphere. Marine Micropaleontology, 2020, 159, 101814 (46p.). 10.1016/j.marmicro.2019.101814. hal-04203142

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https://hal.science/hal-04203142v1

Submitted on 19 Sep 2025

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# An overview and brief description of common marine organic-walled dinoflagellate cyst taxa occurring in surface sediments of the Northern Hemisphere

Van Nieuwenhove Nicolas <fnref n="1" />,*, Head Martin J. <fnref n="2" />, Limoges Audrey <fnref n="3" />, Pospelova Vera <fnref n="4" />,
Mertens Kenneth <fnref n="5" />, Matthiessen Jens <fnref n="6" />, De Schepper Stijn <fnref n="7" />, De Vernal Anne <fnref n="8" />, Eynaud Frédérique <fnref n="9" />,
Londeix Laurent <fnref n="10" />, Marret Fabienne <fnref n="11" />, Penaud Aurélie <fnref n="12" />, Radi Taoufik <fnref n="13" />, Rochon André <fnref n="14" />

## Abstract :

Organic-walled resting cysts of planktonic dinoflagellates occur commonly in modern marine sediment where they represent, with rare exceptions, the only geologically preservable part of the life cycle. Although many species do not produce fossilizable resting cysts, upper Quaternary sediments contain a

<footnote n="1">¹ Department of Earth Sciences, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada</footnote>

<footnote n="2">² Department of Earth Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada</footnote>

<footnote n="3">³ Department of Earth Sciences, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada</footnote>

<footnote n="4">⁴ School of Earth and Ocean Sciences, University of Victoria, PO Box 1700, STN CSC, Victoria, British Columbia V8W 2Y2, Canada</footnote>

<footnote n="5">⁵ Ifremer, LER BO, Station de Biologie Marine, Place de la Croix, BP40537, Concarneau CEDEX F-29185, France</footnote>

<footnote n="6">⁶ Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven D-27568, Germany</footnote>

<footnote n="7">⁷ NORCE Climate, Norwegian Research Centre and Bjerknes Centre for Climate Research, Jahnebakken 5, Bergen NO-5007, Norway</footnote>

<footnote n="8">⁸ Université du Québec à Montréal, Centre GEOTOP, 201 Avenue du Président Kennedy, Montreal, Quebec H3C 3P8, Canada</footnote>

<footnote n="9">⁹ Université de Bordeaux, UMR CNRS 5805 EPOC (Environnements et Paléoenvironnements Océaniques et Continentaux), Allée Geoffroy St Hilaire, Pessac Cedex 33615, France</footnote>

<footnote n="10">¹⁰ Université de Bordeaux, UMR CNRS 5805 EPOC (Environnements et Paléoenvironnements Océaniques et Continentaux), Allée Geoffroy St Hilaire, Pessac Cedex 33615, France</footnote>

<footnote n="11">¹¹ Department of Geography and Planning, School of Environmental Sciences, University of Liverpool, Liverpool L69 7ZT, UK</footnote>

<footnote n="12">¹² UMR 6538 Géosciences Océan, IUEM, Université Brest, CNRS, Plouzané 29280, France</footnote>

<footnote n="13">¹³ Université du Québec à Montréal, Centre GEOTOP, 201 Avenue du Président Kennedy, Montreal, Quebec H3C 3P8, Canada</footnote>

<footnote n="14">¹⁴ Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski, 310 allée des Ursulines, Rimouski, Québec G5L 3A1, Canada</footnote>

<footnote>* Corresponding author : Nicolas Van Nieuwenhove, email address : nvan2@unb.ca</footnote>
diverse cyst record that is used frequently for paleoenvironmental reconstruction and stratigraphic analysis. Reconstructions of past sea-surface conditions rely on an understanding of the distributions of dinoflagellate cysts in modern sediments linked to their respective environmental parameters, underpinned by sound taxonomy and standardized nomenclature. Stratigraphic studies additionally require knowledge of morphological details to distinguish extant from similar extinct taxa. Here, 51 dinoflagellate cyst species and two informal cyst morphotypes that are commonly encountered during routine palynological analysis of upper Quaternary marine sediments from the Northern Hemisphere are briefly described taxonomically and illustrated. In addition, their lowest stratigraphic occurrences are provided.

**Highlights**

► 51 common extant dinoflagellate cyst species and two morphotypes are briefly described and illustrated. ► 2 belong to the Gymnodiniales, 30 to the Gonyaulacales and 21 to the Peridiniales. ► their lowest stratigraphic occurrences are provided.

**Keywords** : Dinoflagellate cysts, marine, Quaternary, Gymnodiniales, Gonyaulacales, Peridiniales
Introduction

Dinoflagellates are protists belonging to the Alveolata (Adl et al., 2019). They are mostly free-living
organisms occupying a wide range of environments from fresh water to the open ocean, and from the
tropics to high latitudes. Dinoflagellates employ a range of trophic strategies including autotrophy,
heterotrophy, and mixotrophy. Of the over 2000 free-living species that have been documented in the
marine realm (Gómez, 2012), around 12-15%, as a conservative estimate, produce a geologically
preservable organic-walled resting cyst (Head, 1996). A smaller proportion of living dinoflagellate
species produce calcareous cysts. Most of these calcareous cysts either do not fully survive the
palynological processing used to concentrate organic-walled dinoflagellate cysts or only leave an
indistinct membrane without a distinguishable fossil record (Head et al., 2006). They are therefore
excluded from the present survey, with the exception of the cysts of *Scrippsiella trifida* which have a
distinctive organic wall that is recognizable as fossil even after the calcareous component has been
removed (Head et al., 2006). Nor does the present survey include cysts produced by *Alexandrium*
species. This genus includes various (sometimes cryptic) species that can produce local blooms with
abundant cysts accumulating in seed beds (e.g., Miyazono et al., 2012; Lacasse et al., 2013; Natsuike et
al., 2013). Most *Alexandrium* species produce morphologically indistinguishable cysts (e.g., Fukuyo, 1985
; John et al., 2014) whose biological affinity can generally only be established through morpho-molecular
studies (e.g., John et al., 2014; Fraga et al., 2015, and references therein). A notable exception is the cyst
of *Alexandrium pseudogonyaulax* (Biecheler, 1952) Horiguchi ex Yuki and Fukuyo, 1992 which can be
identified morphologically and preserves after palynological treatment (see Mudie et al., 2017, and
references therein, for discussion and illustration of the species).

Organic-walled dinoflagellate cysts are frequently used for paleoenvironmental analyses of upper
Quaternary marine records in part because assemblages maintain relatively high taxonomic diversities
across both inner-neritic-oceanic and glacial-interglacial gradients even at relatively high latitudes.
Transfer functions using the modern analogue technique are mostly used for such reconstructions, and
this requires the detailed mapping of cyst distributions in modern sediments, a task begun by Williams
in 1965 (Williams, 1965, 1971), and expanded significantly by Wall et al. (1977), and more recently by de
Vernal et al. (e.g., 1993, 2001, this issue). The importance of a standardized taxonomy and
nomenclature became increasingly apparent during these studies, and was addressed by Rochon et al.
(1999) who provided comparative descriptions, illustrations and distributional maps of 43 taxa
commonly found in modern sediments of the North Atlantic realm. Since then, several taxonomic
studies (e.g., Head et al., 2001, 2006; Pospelova and Head, 2002; Head, 2003; Matsuoka et al., 2009; Li
et al., 2015a; Mertens et al., 2015, 2016; Gurdeike et al., 2018; Limoges et al., 2018; Marret and
Mertens, 2018; Potvin et al., 2018; Van Nieuwenhove et al., 2018; Head et al., this issue; Head and
Mantilla-Duran, this issue) have advanced our understanding of these cysts. The present work updates
Rochon et al. (1999) and incorporates new advances in providing descriptions and lowest stratigraphic
occurrences of 51 dinoflagellate cyst species and two informal cyst morphotypes that are encountered
on a regular basis in Upper Pleistocene through modern marine sediment samples from the Northern
Hemisphere. The taxa illustrated here are considered "common", meaning that they are present in the
surface sediments of at least 40% of the sites from the updated "n = 1968" modern dataset presented by
de Vernal et al. (this issue). For species occurring rarely (i.e., at fewer than 40 sites of the "n = 1968"
dataset), the reader is referred to Limoges et al. (this issue) and Mertens et al. (this issue). For a
footnote regarding the understanding of the concepts of "common" and "rare" as used here, the reader
is referred to Van Nieuwenhove et al. (this issue). Endemic species found in modern sediments of the
Black Sea Corridor are treated in a separate atlas by Mudie et al. (2017), and a brief overview of the
global distribution of selected extant dinoflagellate cyst taxa is also presented in Marret et al. (this
issue). A review of freshwater dinoflagellate cysts is given in Mertens et al. (2012a). All specimens
illustrated here are from Holocene sediments unless stated otherwise.

There is a long tradition of placing dinoflagellate cysts obtained from modern sediments within a fossil
cyst-defined nomenclature, even after they have been linked to an independently named motile stage
by culturing and other experiments (e.g., Reid, 1974). This dual nomenclature is permitted for
dinoflagellates under the International Code of Nomenclature for Algae, Fungi and Plants (ICN; Head et
al., 2016). The present study uses cyst-defined names where they are available, but provides reference
to the equivalent motile-defined (non-fossil) name where it is known. It should be noted that the
distinction recognized under the ICN is between fossil and non-fossil taxa, and that dead cysts in sediment can be treated as fossils because they have stratigraphic relations (Head et al., 2016). Since all cyst-defined taxa treated here are based on types recovered from sediment (or rock), they are effectively fossil-defined taxa and their names can co-exist with those of their equivalent (nonfossil-defined) motile stages. The terminology used in the cyst descriptions mostly follows Williams et al. (2000), but we have opted not to use 'para-' terminology to distinguish cyst features from their motile analogues since only the cyst morphology is addressed. The suprageneric classification used here follows Fensome et al. (1993) unless otherwise stated. For a full synonymy list of each species, the reader is referred to Williams et al. (2017) for the cysts and Guiry and Guiry (2019) for the motile stages, except for recently defined species where synonymies are given in the original publications.

**Systematic part**

Division DINOFLAGELLATA (Bütschli, 1885) Fensome et al., 1993

Class DINOPHYCEAE Pascher, 1914

Subclass GYMNODINIPHYCIDAE Fensome et al., 1993

Order GYMNODINIALES Apstein, 1909

Suborder GYMNODINIINEAE (Autonym)

Family POLYKRIKACEAE Kofoid and Swezy, 1921

**Genus Polykrikos Bütschli, 1873**

**Comments.** A motile-defined genus.

See Mertens et al. (this issue) for cyst of *Polykrikos hartmannii* Zimmermann, 1930 and cyst of *Polykrikos* sp. of Fukuyo (1982).

**Cyst of Polykrikos kofoidii Chatton, 1914**

Plate 1, figs. 1–6

**Distinguishing characters.** A large proximochorate cyst with elongate central body and coarsely reticulate ornamentation. The cyst wall is medium to dark brown, and has a thin smooth solid endophragm, overlain by a thin periphragm from which high, fibrous crests arise, forming an irregular and variable reticulation. The reticulation covers the entire cyst and is loosely organized into five to seven whorls. The crests expand distally, and extend partially or fully over adjacent lumina. The
archeopyle is tremic, occurs at one end of the central body, and has a roundly polygonal outline with a zigzag margin.

**Dimensions.** Length (including crests) 72–134 µm, width (including crests) 48–63 µm, crest height 6–18 µm (Rochon et al., 1999; Matsuoka et al., 2009).

**Remarks.** Prior to 2009, cysts of *Polykrikos kofoidii* were reported as cysts of *Polykrikos schwartzii* and vice versa, due to apparently erroneous attributions of the cysts to their motile stage. This began with Dale (1976, p. 59) incubating a reticulate morphotype and identifying the resulting motile stage as *Polykrikos schwartzii*, and Morey-Gaines and Ruse (1980) reporting that *Polykrikos kofoidii* in culture produced cysts with fibrous cylindrical processes. Matsuoka and Cho (2000) meanwhile recognized four types of surface ornaments on cysts of *Polykrikos*. Re-examination of the cyst-motile relationships and molecular phylogenetic analyses of these two *Polykrikos* species by Matsuoka et al. (2009) showed that cysts of *Polykrikos kofoidii* have a coarse reticulation, whereas cysts of *Polykrikos schwartzii* have a shelf-like ornament. Matsuoka et al. (2009) included the Morey-Gaines and Ruse (1980) morphotype with cylindrical processes within *Polykrikos schwartzii*. We accept this classification but note that further refinements will likely be needed in the future. Because of important apparent intergradation between the ornamentation of both species in certain geographic regions they have also been grouped as the *Polykrikos schwartzii/kofoidii* complex (e.g., Matsuoka et al., 2003; Mudie et al., 2017).

**Lowest stratigraphic occurrence.** Owing to the taxonomic confusion and important morphological intergradation mentioned above, the exact stratigraphic range of the cysts of *Polykrikos kofoidii* is uncertain. The *Polykrikos schwartzii/kofoidii* complex has been widely reported from upper Quaternary including modern sediments (e.g., Harland, 1981) and occasionally reported from the Pliocene (Popescu et al., 2015) and Upper Miocene (e.g., de Verteuil, 1996; Louwye et al., 2007; Kern et al., 2012). *Polykrikos kofoidii* is known from the Lower Pliocene (Gelasian) of the North Sea (as *Polykrikos schwartzii* in Head et al., 2004, fig. 3A.R).

## Cyst of *Polykrikos schwartzii* Rütschli, 1873

Plate 1, figs. 7–9

**Distinguishing characters.** Proximochorate cyst with an elongate central body and cylindrical shelf-like or trumpet-shaped processes. The cyst wall is medium to dark brown and has two or three layers: a smooth solid endophragm and a thin fibrous periphragm forming processes or ridges that cover the entire cysts in even rows. Most processes are hollow with distal ends that are commonly recurved. In some cysts, an incomplete reticulation can be seen, as some rows can be connected. The archeopyle is tremic and has a rounded polygonal outline with a zigzag margin.

**Dimensions.** Length 60–82 µm (including processes), width 41–55 µm (including processes), process height 8.5–14 µm (Matsuoka et al., 2009).

**Remarks.** See under "cyst of *Polykrikos kofoidii***" for nomenclature prior to 2009. The cyst of *Polykrikos schwartzii* differs from those of *Polykrikos kofoidii* in possessing discrete processes rather than a network of ridges.
**Lowest stratigraphic occurrence.** See under "cyst of *Polykrikos kofoidii*". *Polykrikos schwartzii* is known from the Pliocene Kruisschans Sands Member of Belgium (as *Polykrikos kofoidii* in Louwye et al., 2004, fig. 7a-d).

**Cysts of *Polykrikos*? sp. of Kunz-Pirrung, 1998 (ibid. plate 3, figs. 4–13)**

Plate 1, figs. 10–12

**Distinguishing characters.** An informally described group of cysts (see remarks below) from the Arctic Ocean that bears some resemblance to cysts of *Polykrikos kofoidii*. This group includes cysts having a rectangular to elongate outline and a medium to dark brown wall with coarse reticulation. The reticulation varies in height, irregularity, and distribution on the cyst, e., covering the entire cysts, or concentrated at the extremities of the central body. In the latter case, the central (sulcal) area of the cyst can be smooth to scabrate. The archeopyle is tremic.

**Dimensions.** Central body length 46–66 µm, central body width 30–50 µm, reticulation height 1–8 µm (Kunz-Pirrung, 1998).

**Remarks.** These morphotypes differ from cysts of *Polykrikos kofoidii* in often having much-reduced or absent fibrous surface ornamentation. They were first reported from the Laptev Sea as *Polykrikos?* Morphotyp 1, 2 and 3 (Kunz-Pirrung, 1998, pl. 3, figs. 4–13), *Polykrikos?* Typ 1 and 2 (Kunz-Pirrung, 1999, pl. 1, figs. 11, 12; pl. 2, figs. 1, 2), and *Polykrikos* morphotype 1, 2 and 3 but without illustrations in a later publication (Kunz-Pirrung, 2001). Further reports of these morphotypes followed from across the Arctic as cyst of "*Polykrikos* sp. Arctic morphotype" (de Verna et al., 2001), as *Polykrikos* var. arctic/quadratus (Richerol et al., 2008), and as the nomen nudum "*Polykrikos quadratus*" (Bonnet et al., 2012; Zonneveld and Pospelova, 2011). However, phylogenetic analysis reveals that these cysts do not belong within the order Gymnodiniales but are associated with the family Protoperidiniaceae (Potvin et al., 2018).

**Lowest stratigraphic occurrence.** Upper Pleistocene (e.g., Marine Isotope Stage [MIS] 5e of the White Sea; Grøsfjeld et al., 2006).

Subclass PERIDINIPHYCIDAE Fensome et al., 1993

Order GONYAULACALES Taylor, 1980

Suborder GONIODOMINEAE Fensome et al., 1993

Family PYROPHACACEAE Lindemann, 1928

**Comments.** The Goniodomataceae Lindemann, 1928 (as Goniodomaceae in Fensome et al., 1993) is a rejected name (Prud'homme van Reine, 2017) following a recommendation by Elbrächter and Gottschling (2015). We consider the Pyrophacaceae to be an acceptable substitute.
Subfamily HELGOLANDINIOIDEAE Fensome et al., 1993

**Genus *Tuberculodinium* Wall, 1967**

**Comments.** A cyst-defined genus.

**Tuberculodinium vancampoae** (Rossignol, 1962) Wall, 1967

Plate 2, figs. 1–3

**Distinguishing characters.** Flattened subspherical (discoidal) species with inner and outer light brown to yellowish pigmented wall layers separated by numerous short, straight, hollow, barrel-shaped processes that appear circular in surface view. A variable number of processes can have flaring distal extremities that merge with the outer wall layer. The archeopyle is polygonal with one long straight and approximately eight shorter sides, and is epicrystal but not clearly related to the epithecal tabulation (Matsuoka et al, 1998).

**Dimensions.** Central body diameter 63–113 µm (Wall, 1967).

**Biological affinity.** *Pyrophacus steinii* (Schiller, 1915) Wall and Dale, 1971, according to Kobayashi et al. (1986).

**Lowest stratigraphic occurrence.** Lower Oligocene of the Mediterranean region (e.g., Brinkhuis and Biffi, 1993; Torricelli and Biffi, 2001) and North Atlantic (Damassa et al., 1990). Earlier records including the Lower Eocene of the North Sea Basin (Fouhuer and Mohr, 1988) and Upper Eocene of the North Atlantic and Mediterranean regions (e.g., Costa et al. 1988; Brinkhuis, 1992) require verification (El Beialy et al., 2019).

Subfamily PYRODINIOIDEAE Fensome et al., 1993

**Genus *Polysphaeridium* Davey and Williams, 1966 emend. Bujak et al., 1980**

**Comments.** A cyst-defined genus.

**Polysphaeridium zoharyi** (Rossignol, 1962) Bujak et al., 1980

Plate 2, figs. 4–8
**Distinguishing characters.** Spherical central body with microgranulate surface bearing intratabular hollow processes that are distally open with minutely aculeate distal margins. Some process bases may be fused. The archeopyle is epitractal (all plates released on epicyst), with plates being released individually. The archeopyle margin has a characteristic episulcal tab.

**Dimensions.** Central body diameter 40–60 µm (Rossignol, 1962), 31.1–84.8 µm (Mertens et al., 2015b), process length 10–15 µm (Rossignol, 1962), 2.51–21.75 µm (Mertens et al., 2015b).

**Biological affinity.** *Pyrodinium bahamense* Plate, 1906, according to Wall and Dale (1969), Matsuoka (1989) and Mertens et al. (2015b). Strains of this species from both the Atlantic and Pacific oceans are known to produce saxitoxins that can cause paralytic shellfish poisoning (e.g., Landsberg et al., 2006; Lassus et al., 2016).

**Lowest stratigraphic occurrence.** Upper Paleocene (Edwards et al., 1997; Cavagnetto and Guerrero, 1999; Gohn et al., 2000).

Suborder GONYAULACINAE (Autonym)

Family GONYAULACACEAE Lindemann, 1928

Subfamily CRIBROPERIDINIOIDEAE Fensome et al., 1983

**Genus Lingulodinium Wall, 1967 emend. Dodge, 1989**

**Comments.** A cyst-defined genus.

See Limoges et al. (this issue) for *Lingulodinium hemicystum* McMinn, 1991.

**Lingulodinium machaerophorum (Veflandre and Cookson, 1955) Wall, 1967**

Plate 2, figs. 9–12; Plate 3, figs. 1–3

**Distinguishing characters.** Spherical central body with finely granulate surface. Processes are nontabular and hollow, arising from a circular base and tapering distally. Process length can vary from a few micrometers to >30 µm, but is usually fairly uniform for each individual. Processes usually have a smooth surface over most of their length but small spinules often occur over the distal part. The distal ends of the processes are closed and tend towards flattening, and usually terminate as a pointed or blunt tip, but distinctly capitate terminations may occur especially when processes are short. Processes may show slight constriction at their bases. The range of process variability is illustrated by Kokinos and Anderson (1995) and Mertens et al. (2009). Archeopyle formed by loss of between one and six precingular plates, but with the apical plates remaining attached to the sulcus even when all six precingular plates are lost. The margin of the archeopyle has rounded angles.
**Dimensions.** Central body diameter 35–60 µm, process length 0–35 µm (Mertens et al., 2009). Larger diameters were documented by Mertens et al. (2009) but attributed to mechanical deformation of the cysts.

**Remarks.** Differs from *Lingulodinium hemicystum* McMinn, 1991 described from modern sediments of New South Wales, Australia (McMinn, 1991) which is characterized by an epitractal archeopyle (also see Limoges et al., this issue).

**Biological affinity.** *Lingulodinium polyedra* (Stein, 1883) Dodge, 1989, according to Wall and Dale (1966, 1967, 1968), a known producer of yessotoxins (Lassus et al., 2016).

**Lowest stratigraphic occurrence.** Upper Paleocene (Edwards et al., 1984; Heilmann-Clausen, 1985).

**Genus Operculodinium Wall, 1967 emend. Matsuoka et al., 1997**

**Comments.** A cyst-defined genus.

See Limoges et al. (this issue) for *Operculodinium aguinawe* (Stein and Kim, 2009, *Operculodinium crassum* Harland, 1979, *Operculodinium giganteum* Wall, 1957 and *Operculodinium longispinigerum* Matsuoka, 1983.

*Operculodinium centrocarpum* sensu Wall and Dale (1966)

Plate 3, figs. 4–15; Plate 4, figs. 1–9

**Distinguishing characters.** Spherical central body bearing numerous, slender processes whose distribution does not clearly reflect tabulation. Process length varies from long to very short, but is usually uniform on individual specimens. The processes have a smooth surface and are circular in cross-section, hollow, and distally open. They may broaden slightly at their base, and are expanded at the tips. Central body wall is thin (less than 1.0 µm). The surface has scattered granules or columellae, often fine and faintly visible, with interconnecting fibrils sometimes discernible. Archeopyle is formed by loss of the third precingular plate (3") and its margin has rounded angles.

**Dimensions.** Central body diameter 25.5–59.5 µm, process length 0.5–17.5 µm (Mertens et al., 2012b).

**Remarks.** This cyst morphotype was first assigned a paleontological name by Wall and Dale (1966) who recorded these cysts from the western Atlantic plankton (as *Baltisphaeridium centrocarpum*, now *Operculodinium centrocarpum*). Following the realization that these Quaternary cysts are smaller and less robust than *Operculodinium centrocarpum* originally described from the Miocene of Australia (Deflandre and Cookson, 1955), it became customary to refer to these cysts as *Operculodinium centrocarpum* sensu Wall and Dale (1966) (Head 1994b). That practice was followed in Rochon et al. (1999), given uncertainties regarding the cyst–motile relationship of the cyst (Head, 1996). Later, with these uncertainties largely resolved, Paez-Reyes and Head (2013) concluded that this taxon should be referred to the cysts of *Protoceratium reticulatum* (see also Matsuoka et al., 1997). However, genetic studies suggest the presence of cryptic species included in specimens from the type locality of
*Protoceratium reticulatum* (Wang et al., 2019). Therefore, and to be consistent with recent literature, the use of the name *Operculodinium centrocarpum* sensu Wall and Dale (1966) is continued here for this common and cosmopolitan component of the Quaternary dinoflagellate cyst flora.

Three additional morphotypes have been informally described based on variations in the cyst wall ornamentation and the morphological gradation of increasing reduction of process density and length (de Vernal et al., 2001). The "short processes" morphotype (Plate 3, figs. 4–6) has processes that are of normal distribution and diameter but are unusually short, appearing truncated just above the base. The "Arctic morphotype" (Plate 3, figs. 7–13) is characterized by imperfectly developed and sparsely distributed processes. The "cezare morphotype" (Plate 3, figs. 14–15) is characterized by the nearly complete disappearance of processes.

**Biological affinity.** *Protoceratium reticulatum* (Claparède and Lachmann, 1859) Bütschli, 1885 (al. Gonyaulax grindleyi Reinecke, 1967) according to Wall and Dale (1966), a known producer of a number of yessotoxins and toxic metabolic derivates (Lassus et al., 2016).

**Lowest stratigraphic occurrence.** Lower Pliocene (Kurita and Ohashi, 2003; Verhoeven and Louwye 2012; De Schepper et al., 2017). It may range below the Pliocene but its full stratigraphic range is obscured by the widening variation of morphotypes in the lower Neogene and Paleogene.

*Operculodinium israelianum* (Rossignol, 1962) Wall, 1967

Plate 4, figs. 10–12

**Distinguishing characters.** Spherical central body with a thin endophragm and thicker fibroreticulate peripragm. The processes are short solid, and fibrous, with acuminate to minutely expanded tips. The processes widen towards the base where the fibrous nature of the processes is particularly apparent. Processes are distributed over the entire central body but show subtle alignment close to the cingular margins and elsewhere. Archeopore is formed by loss of the third precingular plate (3") and its margin has rounded angles.

**Dimensions.** Central body diameter 40–65 µm, process length 3–10 µm (Rossignol, 1962; Wall, 1967).

**Remarks.** *Operculodinium israelianum* resembles *Operculodinium centrocarpum* sensu stricto, but the processes in general are smaller relative to the central body diameter. For comparison with *Atlanticodinium striaticnulum*, see there.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Occasional occurrence in the Middle–Upper Eocene (Guerstein et al., 2008; González Estebenet et al., 2014), lowest occurrence in the Lower Miocene (e.g., Edwards, 1984; Dybkjær, 2004; Londeix and Lopes, 2014) and upward (e.g., McMinn, 1992; Schreck et al., 2013).

Subfamily GONYAULACOIDEAE (Autonym)
**Genus Ataxiodinium Reid, 1974**

**Comments.** A cyst-defined genus.

See Limoges et al. (this issue) for *Ataxiodinium zevenboomii* Head, 1997.

**Ataxiodinium choane Reid, 1974**

Plate 5, figs. 1–4

**Distinguishing characters.** Proximate species with spherical to broadly elongate or egg shaped central body. A loose outer layer is connected to the central body around the archeopyle margin and elsewhere by variable and irregularly distributed funnel-shaped invaginations. The central body wall is single-layered and solid with a smooth surface. Outer layer is also single-layered, solid and has a faintly microgranular surface. The archeopyle is formed by loss of the third precingular plate, and its margin has well-developed angles. There are no other clear indications of tabulation, although convolutions of the outer layer may weakly reflect the sulcus.

**Dimensions.** Central body length 26–37 µm (Reid 1974).

**Remarks.** *Ataxiodinium zevenboomii* differs in having a more elongate central body and more restricted cavities between central body and outer layer (Head, 1997; Louwye, 2001).

**Biological affinity.** *Gonyaulax spinifera* ( complex ) (Head, 1996). Single-cyst sequencing of *Ataxiodinium choane* shows a phylogenetic position close to *Gonyaulax polygramma* Stein, 1883 (Mertens et al., 2017).

**Lowest stratigraphic occurrence.** Upper Miocene (e.g., Warny, 1999; Brinkhuis et al., 2003; Williams et al., 2004; Schreck et al., 2012) in the Northern Hemisphere, and Lower Oligocene–Middle Miocene in the Southern Hemisphere (Rijleel et al., 2018).

**Genus *Bitectatodinium* Wilson, 1973**

**Comments.** A cyst-defined genus.

**Bitectatodinium? spongium** (Zonneveld, 1997) Zonneveld and Jurkschat, 1999

Plate 5, figs. 5–8

**Distinguishing characters.** Proximate spherical species with a wall comprising a thin pedium and a thicker, fibrous and distally open luxuria. The numerous solid fibers comprising the luxuria have
expanded or acuminate tips. Longer fibers extend beyond the densely fibrous layer. Archeopyle is seldom observed but appears to be formed by the often incomplete loss of one or two precingular plates (Zonneveld and Jurkschat, 1999). There are no other indications of tabulation.

**Dimensions.** Central body diameter 48–63 µm, wall thickness (including fibrous layer) 1.5–3.5 µm, maximum fibre length 5–11 µm (Zonneveld, 1997).

**Remarks.** *Bitectatodinium spongium* differs from the extinct *Bitectatodinium raedwaldii* Head, 1997, described from the Pliocene of eastern England (Head, 1997), which has a luxuria comprising closely spaced pili that may fuse with one another distally as well as possessing a clearly expressed archeopyle defined by the loss of precingular plates 3" and 4".

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Upper Pleistocene (e.g., Esper et al., 2004; Price et al., 2013; Narale et al., 2015).

*Bitectatodinium tepikiense* Wilson, 1973

Plate 5, figs. 9–12

**Distinguishing characters.** Proximate spherical species with a smooth and solid inner wall layer from which arises a dense ornament of erect or subereat lamellae. The lamellae have an approximately even height of a few micrometers. In plan view, the bases of these lamellae appear long and sinuous, sometimes branching into two, and are intercalated with shorter lamellae and rods. The overall pattern often appears densely vermiculate. A small, protuberance may be present. The archeopyle is formed by individual loss of precingular plates 3" and 4", and its margin has well-defined angles.

**Dimensions.** Central body diameter 42–56 µm (Reid, 1974).

**Remarks.** Vermiculate specimens of *Bitectatodinium tepikiense* are very similar to *Filisphaera microornata* (Head et al., 1980); Head, 1994b, described from the Miocene of the Labrador Sea (Head, 1989b, 1989c), which is considered extinct but possibly constitutes a morphological series (Hennissen et al., 2017; Mudie et al., 2017; Matthiessen et al., 2018).

**Biological affinity.** *Gonyaulax digitale* (Pouchet, 1883) Kofoid, 1911, according to Lewis et al. (2001).

**Lowest stratigraphic occurrence.** Occasional occurrences in the Lower (Powell, 1988; Williams et al., 1993) and Middle Miocene of the Porcupine Basin (e.g., Harland 1979; Louwye et al., 2008). The species becomes more frequent in the Pliocene and the Quaternary (see Londeix, 2018).

Genus *Impagidinium* Stover and Evitt, 1978

**Comments.** A cyst-defined genus.
See Limoges et al. (this issue) for *Impagidinium japonicum* Matsuoka, 1983 and *Impagidinium velorum* Bujak, 1984.

**Impagidinium aculeatum** (Wall, 1967) Lentin and Williams, 1981

Plate 6, figs. 1–8

**Distinguishing characters.** Small species with ovoidal central body, small apical protuberance, and finely granulate surface. Sutural septa express tabulation fully over most of the cyst, but are weakly developed or absent in the sulcal area. Most septa become higher gradually towards the gonal junctions, forming a conspicuous point where they merge. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body length 32–35 µm (measured from Jan du Chêne et al., 1986).

**Remarks.** *Impagidinium aculeatum* is distinct from other extant *Impagidinium* species by its small size and spiky coalescence of the septa.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Middle (Firth, 1996) to Upper Eocene (Brinkhuis, 1992; Brinkhuis and Biffi, 1993; Gedl and Leszczynski, 2005), and commonly recorded through the Quaternary (see discussion in Londeix, 2018).

**Impagidinium pallidum** Bujak, 1984

Plate 6, figs. 9–14; Plate 7, figs. 1–3

**Distinguishing characters.** A relatively large, pale species with a spherical central body and thin smooth wall that appears membranous and can be wrinkled, especially at the bases of the sutural septa. The sutural septa are thin and solid with a smooth surface, and can have slightly undulating distal margins. They are absent in the apical area and poorly developed in the ventral area. Cingulum and sulcus shallow. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body diameter (including crests) 49–63 µm (Rochon et al., 1999).

**Remarks.** *Impagidinium pallidum* is distinct from other *Impagidinium* species in its pale appearance and thin, often folded membranous wall. The folds, caused by crumpling of the cyst, frequently make it difficult to discern the gonyaulacacean tabulation as outlined by the sutural septa.

**Biological affinity.** Unknown. A single cyst of the species was sequenced by Mertens et al. (2017).

**Lowest stratigraphic occurrence.** Middle (Head and Norris, 1989) to Upper Eocene (Bujak, 1984; Brinkhuis, 1992), and commonly recorded in the high latitudes through the Quaternary.
*Impagidinium paradoxum* (Wall, 1967) Stover and Evitt, 1978

Plate 7, figs. 4–9

**Distinguishing characters.** Small species with ovoidal central body and finely granulate surface. An apical protuberance is often present. Tabulation well expressed by sutural septa over most of the cyst but weakly developed or absent in the sulcal area. The crest height is more or less constant over the cyst surface. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body length 28–31 µm (measured from Jan du Chêne et al., 1986).

**Remarks.** *Impagidinium paradoxum* differs from *Impagidinium sphaericum* (Wall, 1967) Lentin and Williams, 1981 in its smaller size, more elongate central body, and reduced expression of tabulation in the ventral area.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Possibly recorded from the Eocene (De Coninck and Smit, 1982) or Upper Eocene (De Coninck, 1986; Gruas-Cavagnetto and Babin, 1988), and certainly from the Lower Oligocene (e.g., Head and Norris, 1989; Stover and Hardenbol, 1994; De Coninck, 1995).

*Impagidinium patulum* (Wall, 1967) Stover and Fritt, 1978

Plate 7, figs. 10–12; Plate 8, figs. 1–3

**Distinguishing characters.** Relatively large species with a weakly ovoidal central body and a smooth to weakly and finely granulate surface. The tabulation is well expressed by low sutural septa of uniform height over most of the cyst except in the ventral area. Septa are characteristically absent from the lower cingular margin where it meets the sulcus. Septa have smooth distal margins. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body length 47–65 µm (measured from Jan du Chêne et al., 1986).

**Remarks.** *Impagidinium patulum* is distinguished easily from *Impagidinium sphaericum* by the straight and smooth contact between the septa and cyst surface, and reduced tabulation in the ventral region.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Although some occurrences of *Impagidinium patulum* have been reported from lowermost Paleogene strata (e.g., Head and Norris, 1989; Moshkovitz and Habib, 1993), its first common occurrence is more probably Lower Miocene (see discussion in Londeix, 2018).

*Impagidinium plicatum* Versteegh and Zevenboom, 1995

Plate 8, figs. 4–7
**Distinguishing characters.** Ovoidal to elongate cysts with suturocavate crenulate septa of uniform height except in the sulcal area where they may be lower. The tabulation is well expressed by the crenulate septa over most of the cyst, but may be significantly reduced in the ventral area. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body diameter 24–34 µm, septa height 2–4 µm (Versteegh and Zevenboom, 1995).

**Remarks.** The suturocavate crenulate septa differentiate this species from all other *Impagidinium* species.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Lower Pliocene (Versteegh, 1995, as *Impagidinium* sp. B of Wrenn and Kokinos, 1986; Versteegh and Zevenboom, 1995; De Schepper and Head, 2009) in the Northern Hemisphere. Lower Miocene in the Southern Hemisphere (Bijl et al., 2018).

*Impagidinium sphaericum* (Wall, 1967) Lentin and Williams, 1981

Plate 8, figs. 8–13; Plate 9, figs. 1–6

**Distinguishing characters.** A species with a spherical to ovoidal central body and a finely and faintly granulate surface. A pronounced apical protuberance is often present. The tabulation is well expressed by low sutural septa of approximately uniform height over the central body, including the sulcal area. Both cingular margins bear septa where they meet the sulcus. The bases of septa form somewhat coarse, irregular-looking lines on the central body surface. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body length 4.5–57 µm (Rochon et al., 1999).

**Remarks.** For comparison with similar species, see *Impagidinium paradoxum* and *Impagidinium patulum*.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Recorded from the Lower Miocene (Biffi and Manum, 1988; Byun and Yun, 1992; Londeix and Jan du Chêne, 1998; Oboh-Ikuenobe and Hoffmeister, 1998).

*Impagidinium strialatum* (Wall, 1967) Stover and Evitt, 1978

Plate 9, figs. 7–9

**Distinguishing characters.** Small species with an ovoidal central body and a faintly and finely granulate surface. The relatively high sutural septa have fine radial striae and are of more or less constant height
all over the cyst except in the ventral area. The septa express tabulation incompletely on both dorsal and ventral surfaces. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body diameter 26–38 µm, septa height 5–10 µm (Wall, 1967).

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Lower Miocene (Byun and Yun, 1992; Rochon et al., 1999), with a lowest common occurrence in the Middle Miocene (e.g., McMinn, 1992; Poulsen et al., 1996).

**Genus *Nematosphaeropsis* Deflandre and Cookson, 1955 emend. Wrenn, 1988**

**Comments.** A cyst-defined genus.

**Nematosphaeropsis labyrinthus** (Ostenfeld, 1903) Reid, 1974

Plate 9, figs. 10–12; Plate 10, figs. 1–5

**Distinguishing characters.** Chorate species with an oval central body and smooth to faintly granulate surface. A small apical protuberance may be present. Processes are smooth and exclusively gonal. Their shafts are hollow, slender, and have distal tritifications. The distal tips of the furcations are themselves bifurcate, allowing parallel pairs of ribbon-like trabeculae, each about 1.0 to 1.5 µm wide, to connect with adjacent processes, so that the trabeculae follow the configuration of the plate sutures. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body length 27–42 µm, maximum process length 11–23 µm (Reid, 1974; Rochon et al., 1999).

**Remarks.** *Spiniferites ramosus* (Ehrenberg, 1838) Mantell, 1854 can also have trabeculae that connect the tips of several processes, but these trabeculae are thread-like rather than ribbon-like and seldomly occur in between the tips of all processes. *Nematosphaeropsis rigida* Wrenn, 1988 differs mainly in having trabeculae with a subrounded to subtriangular cross section and solid processes (see also Limoges et al., this issue). The Oligocene to Pleistocene species *Nematosphaeropsis lemniscata* Bujak, 1984 differs in apparently having occasional intergonal as well as gonal processes (Bujak, 1984; Wrenn, 1988), although the reexamination of type material would be needed to confirm this (see also Rochon et al., 1999).

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Rare in the Lower (Bijl et al., 2013) and Middle (Manum et al., 1989) Eocene, more common during the Upper Eocene (e.g., Biffi and Manum, 1988; Gruas-Cavagnetto and Barbin, 1988).

**Genus *Spiniferites* Mantell, 1850 emend. Sarjeant, 1970**
**Comments.** A cyst-defined genus.

See Limoges et al. (this issue) for *Spiniferites hainanensis* Sun and Song, 1992, *Spiniferites multisphaerus* Price and Pospelova, 2014, *Spiniferites ristingensis* Head, 2007 and *Spiniferites septentrionalis* Harland, 1977.

*Spiniferites belerius Reid, 1974*

Plate 10, figs. 6–12

**Distinguishing characters.** Small species having an ovoidal central body. An apical protuberance may be present. The wall is smooth to very finely granulate. Processes are gonal, but one or a few occasional intergonal processes may be present (Limoges et al., 2018). The processes are short, irregularly shaped, either distally trifurcate with recurved bifurcate tips or simple or branched conical structures. Complex membranous processes occur on plate 1P and on the antapical plate. These processes are box-like or trumpet-shaped (Londeix et al., 2018), and may be open or closed distally. Sutural crests are low. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body width 28–37 µm, central body length 35-42 µm, process length 7–10 µm (Londeix et al., 2018).

**Remarks.** *Spiniferites belerius* is distinguished from other *Spiniferites* species by its small and ovoidal central body and relatively short and irregularly shaped processes. This species was discussed in detail by Mertens et al. (2018).

**Biological affinity.** *Gonyaulax scrippsi* Kofoid, 1911 as depicted by Wall and Dale (1968) according to Reid (1974). Some cysts produced in culture by *Gonyaulax baltica* Ellegaard et al., 2002 are very similar to *Spiniferites belerius* (see Limoges et al., this issue), but both species are here treated separately pending further studies (see also Mertens et al., 2018).

**Lowest stratigraphic occurrence.** Lower Miocene (Londeix and Lopes, 2014), with a lowest common occurrence in the Lower Pliocene (Harland, 1979; Dupont, 1998).

*Spiniferites bentorii (Rossignol, 1964) Wall and Dale, 1970*

Plate 11, figs. 1–5

**Distinguishing characters.** Relatively large species having a pear-shaped central body with a smooth to microgranulate surface, and pronounced apical protuberance. Processes are gonal and occasionally intergonal, and may occasionally have fenestrate bases. They are highly variable in shape, ranging from conical to slender and tapering with a wide and curved base, as well as in length, with the longest processes occurring at the antapex. The distal trifurcations are typically V-shaped (Londeix et al., 2018), but can be missing on short or truncated processes. On cingular processes at the lateral margins of the
cyst, furcations typically project at 90° to the process length and parallel with the central body surface (Head, 2007, fig. 7j,k). Sutures are marked by low septa. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body width 45–63 µm, central body length 58–73 µm, process length up to 20 µm (Reid, 1974; Londeix et al., 2018).

**Remarks.** *Spiniferites bentorii* is distinguished from *Spiniferites lazus* Reid, 1974, which also has fenestrate process bases, by its pear-shaped central body.

**Biological affinity.** *Gonyaulax digitale* (Pouchet, 1883) Kofoid 1911, according to Wall and Dale (1967, p. 352) and Dodge (1989, p. 283).

**Lowest stratigraphic occurrence.** Recorded from the Lower Miocene (e.g. Edwards, 1986; Powell, 1986) and common through the Quaternary. Older occurrences are considered problematic (Londeix, 2018).

*Spiniferites bulloideus* (Deflandre and Cookson, 1955) Sarjeant, 1970 sensu Wall (1965)

Plate 11, figs. 6–12

**Distinguishing characters.** Small species having a small, subspherical to ovoidal central body with a smooth surface. Processes are gonal, slender and delicate, and relatively long compared to the size of the central body. Sutural crests are low but well expressed. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body width 28–39 µm, central body length 32–42 µm, process length up to 16 µm (Wall and Dale, 1968).

**Remarks.** *Spiniferites bulloideus* was originally described by Deflandre and Cookson (1955) from the Miocene of Australia as a small (30–37 µm) spheroidal cyst with a thin, delicate wall bearing slender processes 10–15 µm long that are gonal and occasionally intergonal. The Quaternary specimens designated as *Spiniferites bulloideus* sensu Wall (1965) are probably not conspecific with the holotype (i.e., *Spiniferites bulloideus* sensu stricto, which is probably synonymous with *Spiniferites ramosus*) and differ from it by their two prominent antapical processes, membranous developments, and the lack of intergonal processes (see Mertens et al., 2018, for further discussion). *Spiniferites bulloideus* is closely similar to, albeit slightly more delicate and smaller than, *Spiniferites ramosus*. However, *Spiniferites ramosus* is known to show wide intraspecific variation and *Spiniferites bulloideus* has often been grouped with *Spiniferites ramosus* (e.g., Rochon et al., 1999) or unidentified *Spiniferites* spp. (e.g., Zonneveld et al., 2013). The dinoflagellate *Gonyaulax baltica* described from the Baltic Sea (Ellegaard et al., 2002) produces cysts with a wide range of morphologies including forms that are similar to *Spiniferites bulloideus*, but these Baltic Sea forms generally have wider, stout processes and more septal development than *Spiniferites bulloideus* sensu Wall (1965).

**Biological affinity.** Related to *Gonyaulax scrippsae* Kofoid, 1911, by Wall and Dale (1967). However, their specimen appears quite different from the description and specimens designated as *Spiniferites*
*bulloideus* sensu Wall (1965) in recent studies (e.g., Mertens et al., 2018) and here, and unresolved questions remain concerning its biological affinity.

**Lowest stratigraphic occurrence.** The lowest common occurrence of *Spiniferites bulloideus* sensu stricto is in the Lower Eocene (e.g., Auffret and Gruas-Cavagnetto, 1975; De Coninck, 1975; also see discussion in Londeix, 2018). The lowest occurrence of *Spiniferites bulloideus* sensu Wall, 1965 is probably Lower Miocene (e.g., Londeix and Jan du Chêne, 1998), but records of this species are mostly from the Holocene.

*Spiniferites delicatus* Reid, 1974

Plate 12, figs. 1–6

**Distinguishing characters.** Species having an ovoidal central body, apparently with a thick bilayered wall characterized by radial columellae and a thin outer wall layer that is granulate to microreticulate (Reid, 1974). Processes are membranous and gonal only, with petaloid process tips. The attachment of the well-developed septa along the process shafts gives the impression of "skeletal rods" supporting the processes. High and membranous sutural septa link adjacent processes. Surfaces of the processes and septa are granulate. Archeopyle formed by loss of peculiar plate 3".

**Dimensions.** Central body width 35–54 µm, central body length 37–60 µm, process length up to 29 µm (Gurdebeke et al., 2018; Londeix et al., 2018).

**Remarks.** *Spiniferites ristingensis* Head, 2007 has similar processes with petaloid distal terminations, but differs in its distinctive wall structure in which a smooth inner layer is surmounted by an outer layer forming small, densely distributed blisters and hollow undulations over the surface (Head, 2007). The septa linking adjacent processes are lower than for *Spiniferites delicatus*. However, the differences between these species are subtle and they have been grouped together (e.g., Ribeiro et al., 2016). The holotype and topotype specimens of *Spiniferites delicatus* have been examined by Gurdebeke et al. (2018) although fine detail of the wall structure remain elusive. See also Limoges et al. (this issue).

**Biological affinity.** Unknown, but probably *Gonyaulax* sp. (Rochon et al., 1999).

**Lowest stratigraphic occurrence.** Lower Oligocene (De Coninck, 2001), and more common in the Lower Miocene (e.g., Londeix and Jan du Chêne, 1998; Londeix and Lopes, 2014).

*Spiniferites elongatus* Reid, 1974 emend. Van Nieuwenhove et al., 2018

Plate 12, figs. 7–10; Plate 13, figs. 1–12

**Distinguishing characters.** Large species having a characteristic ellipsoidal to cylindriform elongate central body with a smooth to finely granulate outer wall and smooth inner wall. Processes gonal only, tapering, and connected by proximally hollow septa that vary in height from discrete ridges to well-
developed membranes and usually are higher at the apex and notably towards the antapex. The hollow nature of the septa may result in prominent cavation, especially antapically, and discrete lines can often be seen at the margins of the plates indicating where the inner and outer layers detach. Tabulation is only weakly expressed in the sulcal area. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body width 23–41 µm, central body length 42–64 µm, process length 5–22 µm (Van Nieuwenhove et al., 2018).

**Remarks.** *Spiniferites elongatus* displays wide variation in the length and development of the processes and septa. The processes can be short with pointed or blunt, bulbous endings that appear to sit on the crests of septa, or long and well developed with distally hollow and open subconical antapical processes, and all morphologies in between. The septa connecting the processes can range from low rudimentary crests to membranes as high as the adjoining process stems. The "elaborate" morphologies with long processes and well developed membranes conform with the description of similarly elongate cysts, *Spiniferites frigidus* Harland and Reid in Harland et al., 1980 and *Rottnestia amphicavata* Dobell and Norris in Harland et al., 1980, but based on the morphological continuum between those two species and *Spiniferites elongatus*, and supported by molecular data, Van Nieuwenhove et al. (2018) considered both *Spiniferites frigidus* and *Rottnestia amphicavata* to be junior synonyms of *Spiniferites elongatus*. However, these authors also suggested the use of two informal types during routine counting: *Spiniferites elongatus* – Norwegian morphotype for elongated cysts with strongly reduced processes bearing blunt terminations; and *Spiniferites elongatus* – Beaufort morphotype for elongated cysts with well-developed septa all over the cyst and the antapical crest height at least half the length of the antapical processes.

**Biological affinity and nomenclature.** On the basis of culturing experiments, Ellegaard et al. (2003) transferred the cyst-defined species *Spiniferites elongatus* to the motile-defined genus *Gonyaulax*, as *Gonyaulax elongata*, in order to join both the motile stage and the cyst under a single name. We prefer to retain the name *Spiniferites elongatus* following dual nomenclature as sanctioned under the ICN (Head et al., 2016).

**Lowest stratigraphic occurrence.** Upper Miocene of the Nordic Seas (Manum et al., 1989; Schreck et al., 2013) and western Pacific (Bujak and Matsuoka, 1986), and commonly recorded through the Quaternary. The specimen illustrated as *Spiniferites aff. elongatus* from the Lower Oligocene of Belgium (De Coninck, 2001, pl. 11, fig. 3) is very similar to the modern forms.

*Spiniferites hyperacanthus (Deflandre and Cookson, 1955) Cookson and Eisenack, 1974*

Plate 14, figs. 1–3

**Distinguishing characters.** Large species having a broadly ovoid to spheroidal central body. Surface of outer wall is smooth to finely granulate. Processes are both gonal and intergonal, typically slender, and distally furcate with recurved bifurcate tips. At least one intergonal process is present on every major suture. Sutural crests vary from nearly absent to low, and are not higher at the antapex than anywhere else. Archeopyle formed by loss of precingular plate 3".
**Dimensions.** Central body length 54–59 µm, process length 13–20 µm (Deflandre and Cookson, 1955), but see remarks below.

**Remarks.** Two informal types were distinguished by Limoges et al. (2018): specimens with short processes (<3 µm) can be referred to as *Spiniferites hyperacanthus* – short-processed morphotype, and specimens with three or more intergonal processes between adjacent gonal processes can be referred to as *Spiniferites hyperacanthus* – multi-intergonal morphotype.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Described from the “Miocene or older” of Australia (Deflandre and Cookson, 1955), this species has regular occurrences from the Lower Eocene (e.g., De Coninck, 1965; Gruas-Cavagnetto, 1970; Fechner and Mohr, 1988). Illustrations of older specimens (e.g., Cookson and Eisenack, 1974; Jan du Chêne, 1988; Kirsch, 1991; Slimani et al., 2010) generally do not conform to the typical morphological characteristics of this species.

**Spiniferites lazus Reid, 1974**

Plate 14, figs. 4–10

**Distinguishing characters.** Species having an elonate ovoidal central body with a moderately thick wall and a finely granulate to microreticulate surface. May have a small apical protuberance. Processes are gonal with expanded and fenestrate bases. Sutural crests are low. Archeopyle formed by loss of precingular plate 3”.

**Dimensions.** Central body width 30–40 µm, central body length 42–58 µm, process length 12–25 µm (Gurdebeke et al., 2018; Reid, 1974).

**Remarks.** The central body outline and surface ornamentation of *Spiniferites lazus* resemble that of the late Quaternary species *Spiniferites septentrionalis* Harland, 1977, but the latter has marked fenestrate petaloid process terminations and lacks broad fenestrate process bases.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Occasionally recorded in the Upper Oligocene (Strauss, 1993) and Neogene (Strauss et al., 2001), common from Middle/Upper Pleistocene (de Verteuil, 1996; Combourieu-Nebout et al., 1999; Eynaud et al., 2016).

**Spiniferites membranaceus (Rossignol, 1964) Sarjeant, 1970**

Plate 15, figs. 1–9

**Distinguishing characters.** Species having a broadly ovoidal central body and a nearly smooth to microgranular or microrugulate surface. Processes are gonal and distally furcate with recurved bifurcate
tips. Sutural crests are low, except at the antapex where a conspicuous granular flange is present along the 4"/1"" suture connecting the two slender dorso-antapical processes. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body width 34–42 µm and central body length 36–44 µm in topotype material (Gurdebeke et al., 2018), up to 50 and 57 µm, respectively, according to Londeix et al. (2018); process length 12–25 µm.

**Remarks.** Unfavorable orientation can make it difficult to distinguish *Spiniferites membranaceus* from *Spiniferites belerius*, which has more pronounced, trumpet-shaped antapical processes. These species were grouped together in Rochon et al. (1999), but *Spiniferites membranaceus* was reported as a separate species in more recent versions of the database (de Vernal et al., 2001, 2013, this issue).

**Biological affinity and nomenclature.** On the basis of culturing experiments, Ellegaard et al. (2003) transferred the cyst-defined species *Spiniferites membranaceus* to the motile-defined genus *Gonyaulax*, as *Gonyaulax membranacea*, in order to join both the motile stage and the cyst under a single name. We prefer to retain the name *Spiniferites membranaceus* following dual nomenclature as sanctioned under the ICN (Head et al., 2016).

**Lowest stratigraphic occurrence.** Spiniferate cysts with a high antapical crest have often been identified as *Spiniferites membranaceus* (or taxonomically equivalent names) but such specimens not always conform to the morphological criteria of the type material (Rossignol, 1964) making it difficult to confirm the lowest occurrence of this species. The name *Spiniferites membranaceus* has been applied to specimens from the upper Lower Cretaceous of, Foucher, 1979; Kirsch, 1991; Aleksandrova and Zaporozhets, 2008; Tabără et al., 2017).

*Spiniferites mirabilis* (Rossignol, 1964) Serjeant, 1970 emend. Limoges et al., 2018

Plate 16, figs. 1–6

**Distinguishing characters.** Large species having a broadly ovoidal to spheroidal central body, and a smooth to finely granulate surface. Processes are both gonal and intergonal, and distally furcate with recurved bifid tips. At least one intergonal process is present on every major suture. Sutural crests vary from nearly absent to moderately high, except at the antapex where a conspicuous flange runs along the dorsal suture of the antapical plate. The number of intergonal processes integrated in the flange ranges from only a few to up to 10 (Limoges et al., 2018). Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body width 35–76 µm, central body length 40–84 µm, process length up to 22 µm (Limoges et al., 2018; Londeix et al., 2018).

**Remarks.** Two subspecies have been retained based on the number and shape of the intergonal processes. *Spiniferites mirabilis* subsp. *mirabilis* (autonym) has at least one intergonal process per major suture, whereas *Spiniferites mirabilis* subsp. *serratus* Limoges et al. 2018 has at least three, shorter and flatter intergonal processes between each pair of adjacent gonal processes.
*Spiniferites mirabilis* is distinguished from *Spiniferites membranaceus* most clearly by its intergonal processes, and from *Spiniferites hyperacanthus* in having a well-developed antapical flange. Unfavorable orientation can hamper the observation of the antapical flange, and *Spiniferites mirabilis* and *Spiniferites hyperacanthus* are often grouped as *Spiniferites mirabilis* s.l. (e.g., Rochon et al., 1999).

**Biological affinity.** Related to *Gonyaulax spinifera* (Claparède and Lachmann, 1859) Diesing, 1866, according to cyst-theca experiments by Wall and Dale (1967, 1968), Sonneman and Hill (1997) and Morquecho et al. (2009). The *Gonyaulax spinifera* complex is associated with the production of yessotoxins, but the production of these toxins appears restricted to specific strains of the complex and needs further investigation (Lassus et al., 2016).

**Lowest stratigraphic occurrence.** Lower Eocene (e.g., Costa and Downie, 1979; Brown and Downie, 1984; Islam, 1984; Cocozza and Clarke, 1992), possibly the Lower Paleogene (Jan du Chêne, 1988; Eshet et al., 1992), and commonly recorded through the Quaternary (also see Discussion in Londeix, 2018).

*Spiniferites pachydermus* (Rossignol, 1964) Reid, 1974

Plate 16, figs. 7–14

**Distinguishing characters.** Large species having an ovoidal central body with a thick and granulate to quasi-reticulate wall. Processes gonal, long and tapering with concave sides and a smooth to scabrate surface, and distally trifurcate with bifid tips. Septa low to membranous. Archeopyle formed by loss of precingular plate 3".

**Dimensions.** Central body width 50–52 µm, central body length 60–61 µm, process length 17–19 µm (Londeix et al., 2018).

**Remarks.** Restudy of topotype material is required to determine the exact nature of the wall structure.

**Biological affinity.** *Gonyaulax eiluojardiae* Mertens et al., 2015a, according to Mertens et al. (2015a).

**Lowest stratigraphic occurrence.** Middle Miocene (e.g., Mudie, 1989; Matsuoka, 1983).

*Spiniferites ramosus* (Ehrenberg, 1838) Mantell, 1854

Plate 17, figs. 1–9

**Distinguishing characters.** Smaller species having a broadly ovoidal to spherical central body and a smooth to scabrate wall surface. Processes are gonal (but see remarks), long and hollow, and have long distal furcations with bifurcate tips. Occasionally, narrow thread-like trabeculae are present between adjacent process tips. The low sutural septa rise slightly towards the processes to which they connect. Archeopyle formed by loss of precingular plate 3".
**Dimensions.** Central body width 33–42 µm, central body length 30–48 µm, process length 13–25 µm (Rochon et al., 1999; Londeix et al., 2018). Note that slightly smaller cysts (width 25–34 µm, length 31–40 µm) with shorter processes (3–14 µm) have also been observed, notably in culture studies (Lewis et al., 1999).

**Remarks.** *Spiniferites ramosus* shows wide intraspecific variation. In addition to the autonomous subsp. *ramosus* for the typical forms, Londeix et al. (2018) also retained subsp. *multiplicatus* (Rossignol, 1964) Lentin and Williams, 1973 (sensu Londeix et al., 2018) to accommodate specimens showing an occasional presence of up to one intergonal process on one or several sutures; this in contrast to the larger *Spiniferites hyperacanthus*, where at least one intergonal process is present on all sutures. The morphology of *Spiniferites ramosus* in relation to the similar *Spiniferites bulloideus* is discussed in detail by Mertens et al. (2018).

**Biological affinity.** Cysts corresponding with the morphological concept of *Spiniferites ramosus* followed here were related to *Gonyaulax spinifera* by Lewis et al. (1999) and Rochon et al. (2009). The *Gonyaulax spinifera* complex is associated with the production of yessotoxin that appears restricted to specific strains of the complex and needs further investigation (Lassus et al., 2016).

**Lowest stratigraphic occurrence.** Many morphologies have been identified as *Spiniferites ramosus* and its various subspecies, obscuring the stratigraphic range of this taxon. Specimens identified as *Spiniferites ramosus* (or taxonomically equivalent names) date back to the earliest Cretaceous, or possibly even the Late Jurassic (see discussion in Londeix, 2018).

Subfamily UNCERTAIN

**Genus Atlanticodinium Head and Mantilla-Duran, this issue**

**Comments.** A cyst-defined genus.

**Atlanticodinium striicontinum** Head and Mantilla-Duran, this issue

Plate 18, figs. 1–6

**Distinguishing characters.** A spherical to ovoidal central body with a granulate surface. Processes have a dense, nontabular distribution. They vary from hollow cones with rounded tips to verrucae and bacculae, have striations along their inner surface, and are distally closed. Granules on central body surface continue beneath process bases, where they are pronounced. The archeopyle is precingular, formed by loss of plate 3", the margins of which have well defined angles. The operculum is free.

**Dimensions.** Central body diameter 30 (39.2) 49 µm (N=24), process length 1.8 (2.8) 4.8 µm (N=28) (Head and Mantilla-Duran, this issue).

**Remarks.** This species was referred to as *Operculodinium* sp. cf. *Operculodinium janduchenei* Head et al., 1989b in Rochon et al. (1999) and as *Operculodinium* sp. A in Vink et al. (2000). *Atlanticodinium* (formerly *Operculodinium*) *janduchenei* (Head et al., 1989b) Head and Mantilla-Duran, this issue,
described from the Upper Miocene of the Labrador Sea, differs in having distally open or closed
processes, with both sometimes present on the same specimen. These processes lack the striations
found in *Atlanticodinium striaticonulum*. *Atlanticodinium janduchenei* also lacks the pronounced
granulation beneath process bases that characterizes *Atlanticodinium striaticonulum*. *Operculodinium
israelianum* differs in having a fibroreticulate outer wall layer and intratabular process distribution
whereas *Atlanticodinium striaticonulum* has a granulate outer wall and nontabular processes. Also,
*Operculodinium israelianum* has an archeopyle margin with rounded angles, whereas they are well
defined in *Atlanticodinium striaticonulum*.

**Lowest stratigraphic occurrence.** Possibly upper Lower Pliocene and certainly Lower Pleistocene (Head and Mantilla-Duran, this issue).

**Genus Pyxidinopsis Habib, 1976**

**Comments.** A cyst-defined genus.

**Pyxidinopsis reticulata** McMinn and Sun, 1994 emend. Marret and de Vernal, 1997

Plate 18, figs. 7–11

**Distinguishing characters.** Small, (sub)spherical proximate species with an irregular, nontabular reticulation of low muri. Muri are of variable height ranging between 1.0 and 2.5 µm. Lumen are less than 3 µm in diameter with a microgranulate to finely corrugate/striate surface. When low striations are present they originate from and are mostly perpendicular to the muri. Archeopyle formed by loss of precingular plate 3"; no other indications of tabulation.

**Dimensions.** Central body diameter 23–40 µm (McMinn and Sun, 1994; Marret and de Vernal, 1997).

**Remarks.** The Pliocene–Pleistocene species *Corrudinium harlandii* Matsuoka, 1983 appears to be larger (40–53 µm) with higher muri up to 5 µm (n = 25 specimens; Matsuoka, 1983), although detailed morphometric studies are needed to confirm these trends. Indeed, the morphologies of *Corrudinium harlandii* and *Pyxidinopsis reticulata* show overlap around the Pliocene/Pleistocene transition, making them difficult to differentiate (De Schepper and Head, 2009). *Corrudinium? labradori* Head et al., 1989b differs from both these species by being smaller (25–31 µm; Head et al., 1989b), possessing a 2P archeopyle, and the clear expression of one cingular margin via a finely undulating crest.

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Regular occurrences are reported from the Lower Pliocene (De Schepper and Head, 2009; Mahdavijourshari, 2014). Possibly occurs in the Lower Miocene (Bijl et al., 2018), but older occurrences (e.g., Xu et al., 1997) are ambiguous because of potential morphological overlap with *Corrudinium harlandii* in the Pliocene (see remarks above).
**Pyxidinopsis reticulata** – Okhotsk morphotype of Bonnet et al. (2012)

Plate 18, figs. 12–14

**Distinguishing characters.** Small, (sub)spherical proximate morphotype with an irregular, nontabular reticulation formed by muri. A primary reticulation is formed by muri that are higher than muri present within the lumina that form a complete to incomplete sub-reticulation. In case of an incomplete sub-reticulation, the appearance of the lumina is striated. Archeopyle formed by loss of precingular plate 3", with no other indications of tabulation.

**Dimensions.** Diameter 35–40 µm.

**Remarks.** Compared to typical *Pyxidinopsis reticulata*, the Okhotsk morphotype possesses a more pronounced and complex inner reticulation (Bonnet et al., 2012, illustrated in supplementary material).

**Biological affinity.** Unknown.

**Lowest stratigraphic occurrence.** Only observed in surface sediment samples in the Okhotsk Sea (Bonnet et al., 2012, 2013).

Order PERIDINIALES Haeckel, 1894

Suborder PERIDINIINEAE (Autonym)

Family PROTOPERIDINIACEAE Balech, 1988

Subfamily PROTOPERIDINIOIDEAE Balech, 1938

**Genus *Brigantedinium* Reid, 1977 x Lentin and Williams, 1993**

**Comments.** A cyst-defined genus.

See Mertens et al. (this issue) for *Brigantedinium asymmetricum* Matsuoka, 1987 ex Head, 1996, *Brigantedinium auranteum* Reid, 1977 ex Lentin and Williams, 1993, and *Brigantedinium majusculum* Reid, 1977 ex Lentin and Williams, 1993.

**Brigantedinium cariacoense** (Wall, 1967) Lentin and Williams, 1993

Plate 19, fig. 1

**Distinguishing characters.** Spherical species with a light brown to dark brown wall. Surface is smooth, often crumpled or folded, and no visible separation of wall layers under the light microscope. The archeopyle is intercalary (2a) and typically elongated hexagonal, with its breadth almost twice its height.
There may be splitting of the cyst wall around the archeopyle. The adapical margin of the archeopyle is characteristically convex. There are no other indications of tabulation.

**Dimensions.** Cyst diameter 36–63 µm (Wall, 1967; Harland, 1977; Reid, 1977; Matsuoka, 1987).

**Remarks.** Unambiguous identification of this species can only be made when the archeopyle is clearly visible. If not, it is grouped with other round brown cysts as indeterminate *Brigantedinium* spp. Semi-diagrammatic illustrations of the archeopyle of various *Brigantedinium* species are provided by Matsuoka (1987) and by Mertens et al. (this issue).

**Biological affinity.** *Protoperidinium avellana* (Meunier, 1919) Balech, 1974, according to Wall and Dale (1968), Lewis et al. (1984) and Sonneman and Hill (1997).

**Lowest stratigraphic occurrence.** Middle Miocene, offshore New Jersey, de Verteuil, 1996).

*Brigantedinium simplex* Wall, 1965 ex Lentin and Williams, 1993

Plate 19, figs. 2–7

**Distinguishing characters.** Spherical to oblique-dorsally compressed species with a brown to dark brown wall. Surface is smooth to lightly ornamented, often crumpled or folded, and there is no visible separation of wall layers under the light microscope. The archeopyle is intercalary (2a), hexagonal trapezoidal, with height and breadth approximately equal to the cyst radius. The cingular margins are sometimes slightly raised, and two depressions may occur in the ventral region representing flagellar scars. There are no other indications of tabulation.

**Dimensions.** Cyst diameter 29–54 µm (Wall, 1965; Harland, 1977; Reid, 1977; Matsuoka, 1987).

**Remarks.** Unambiguous identification of this species can only be made when the archeopyle is clearly visible. If not, it is grouped with other round brown cysts as indeterminate *Brigantedinium* spp. The hexagonal archeopyle of *Brigantedinium simplex* is somewhat comparable in shape to that of *Brigantedinium majuscuum*, but the latter species is distinguished by its larger cyst size. Semi-diagrammatic illustrations of the archeopyle of various *Brigantedinium* species are provided by Matsuoka (1987) and by Mertens et al. (this issue).

**Biological affinity.** *Protoperidinium conicoides* (Paulsen, 1905) Balech, 1973, according to Wall and Dale (1968) and Lewis et al. (1984), among others.

**Lowest stratigraphic occurrence.** Occasionally recorded from the Lower to Middle Miocene (Paredes et al., 2015; Bijl et al., 2018), and commonly recorded from the Upper Miocene (e.g., Bujak, 1984; Matsuoka et al., 1987; Kurita and Obuse, 2003).

Genus *Islandinium* Head et al., 2001 emend. Potvin et al., 2013

**Comments.** A cyst-defined genus emended by Potvin et al. (2013) to include the motile stage.
See Mertens et al. (this issue) for *Islandinium pacificum* Gurdebeke et al., 2019a.

*Islandinium brevispinosum* Pospelova and Head, 2002

Plate 19, figs. 8–9

**Distinguishing characters.** A small pale brown or brown spherical cyst with smooth wall surface and numerous solid spinules. The spinules are similar in length and shape, densely and irregularly distributed over the entire cyst, and have acuminate or blunt tips. Central body wall is ≤ 0.3 µm thick with no visible indication of tabulation. Saphopylic archeopyle is formed by loss of three apical plates (2', 3', 4').

**Dimensions.** Central body diameter 18–25 µm, spinule length varies from low bumps to up to 3.5 µm (Pospelova and Head, 2002).

**Remarks.** Liu et al. (2014) described cysts produced by *Protoperidinium haizhouense* Liu, Gu and Mertens in Liu et al., 2014 that are very similar to *Islandinium brevispinosum* but feature a saphopylic archeopyle formed by loss of two apical plates (2', 4').

**Biological affinity.** Protoperidiniacean cysts, possibly produced by *Protoperidinium haizhouense* (observations made by KNM).

**Lowest stratigraphic occurrence.** Upper Pleistocene (e.g., Pospelova et al., 2015).

*Islandinium? cezare* (de Vernal et al., 1989; de Vernal in Rochon et al., 1999) *Head et al.*, 2001

Plate 19, figs. 10–12; Plate 20, figs. 1–6

**Distinguishing characters.** Brown spheroidal central body with numerous nontabular erect processes which are variable in length. The central body wall is thin (<0.3 µm) and the surface is smooth to granular. Processes are usually solid with a small pericoel at the base. Processes are circular in cross section. Process bases are 0.8–1.8 µm across and are separated from one another by about 2–3 µm in the type material. Process tips are minutely expanded into platforms with recurved margins appearing mushroom-like in longitudinal section. Archeopyle unknown.

**Dimensions.** Central body maximum diameter 23–42 µm, process length 4–8 µm, based on the type material and morphotype 1 of Head et al. (2001).

**Remarks.** Head et al. (2001) recognized three morphotypes: the type material from the Upper Pleistocene of Quebec, and morphotypes 1 and 2 from modern sediments of the Kara Sea. These three morphotypes were grouped as *Islandinium? cezare* sensu lato, with morphotype 1 being more similar morphologically to the type material. It was nonetheless noted that morphotype 1 was more variable than the type material. Morphotype 2, characterized by one or more minute barbs on the process stems and since determined to have a saphopylic apical archeopyle, has now been placed within *Islandinium minutum* subsp. *barbatum* (Potvin et al., 2018). The questionable generic assignment of *Islandinium? cezare* sensu lato reflects the uncertain style of archeopyle formation, which is called even more into
question now that Morphotype 2 has been removed from this taxon. In the database, *Islandinium? cezare* and *Islandinium minutum* subsp. *barbatum* are combined as *Islandinium? cezare* sensu lato.

**Biological affinity.** Unknown, but specimens of *Islandinium? cezare* including those illustrated here can be very similar to the cysts produced by *Islandinium tricingulatum*.

**Lowest stratigraphic occurrence.** Upper Pleistocene (e.g., Grøsfjeld et al., 2006).

*Islandinium minutum* (Harland and Reid in Harland et al., 1980) Head et al., 2001 emend. Potvin et al., 2013 subsp. *minutum* (Autonym)

Plate 20, figs. 7–12; Plate 21, figs. 1–8

**Distinguishing characters.** Light to dark brown spheroidal central body, with numerous nontabular erect processes. The central body wall is thin (<0.5 µm) and the surface has low verrucae or low coni. Processes have a smooth surface and a circular cross-section. They are mostly solid to apiculocavate, tapering distally, terminating in finely acuminate tips. Process bases are not evenly distributed and are separated from one another by between 1.5 and 4.0 µm. Processes have a maximum diameter ranging from about 1.0 to 1.5 µm and are variable in length. Process surfaces appear smooth under light microscopy. The archeopyle is saphopylic, formed by loss of three apical plates (2', 3', 4'). The canal plate may be released during archeopyle formation.

**Dimensions.** Central body maximum diameter: 20–50 µm, process length 3.5–7.0 µm (Head et al., 2001).

**Remarks.** *Islandinium minutum* subsp. *minutum* (autonym) differs from *Islandinium minutum* subsp. *barbatum* in having process surfaces that are smooth under light microscopy, although minute barbs have been observed under SEM (Potvin et al., 2018) making the distinction between these two subspecies less clear.

**Biological affinity.** Potvin et al. (2018) emended the description of *Islandinium minutum*, a cyst-defined genus and species, to accommodate the motile cell.

**Lowest stratigraphic occurrence.** Upper Pliocene. It may occur in the Middle Miocene (unillustrated in de Verteuil, 1996) but confirmation is needed owing to taxonomic uncertainties (Head et al., 2001).

*Islandinium minutum* (Harland and Reid in Harland et al., 1980) Head et al., 2001 emend. Potvin et al., 2013 subsp. *barbatum* Potvin, Kim, Yang and Head in Potvin et al. 2018

Plate 21, figs. 6–11; Plate 22, figs. 1–3

**Distinguishing characters.** Brown spheroidal central body with numerous nontabular erect or curved processes. The central body wall is thin (about 0.3 µm or less) and the surface is weakly or prominently ornamented with low verrucae or low coni. Processes have a circular cross-section and are solid except for a small pericoel usually present at process bases. Processes taper distally to minutely expanded tips that are resolved as conjoined barbs under SEM. Process stems are ornamented by numerous barbs that might appear as verrucae/granules in light microscopy. These barbs point towards the cyst surface.
Process bases are not evenly distributed and are separated from one another by between 1.5 and 7.1 µm. Process length is about one-fifth to two-fifths of the central body diameter. The archeopyle is saphopylic, formed by loss of three apical plates (2', 3', 4'). The canal plate may be released during archeopyle formation.

**Dimensions.** Central body maximum diameter 25–51 µm, average process length 6.8–12.9 µm (Potvin et al., 2018).

**Remarks.** This subspecies was previously described as *Islandinium? cezare* morphotype 2 by Head et al. (2001). *Islandinium minutum* subsp. *barbatum* is combined with *Islandinium? cezare* in the database.

**Biological affinity.** Unknown but molecular phylogeny shows a close relationship with *Islandinium minutum* subsp. *minutum* (Potvin et al., 2018).

**Lowest stratigraphic occurrence.** Presently only known from Arctic Ocean surface sediments (Head et al., 2001, as *Islandinium? cezare* s.l. (morphotype 2); Potvin et al. 2018).

**Genus Lejeunecysta Artzner and Dörhöfer, 1978 emend. Lentin and Williams, 1976**

**Comments.** A cyst-defined genus.

See Mertens et al. (this issue) for *Lejeunecysta? epidemic* Matsuoka, 1987 and *Lejeunecysta marieae* (Harland in Harland et al., 1991) Lentin and Willian. 1993.

**Lejeunecysta oliva (Reid, 1977) Turon and Londeix, 1988**

Plate 22, figs. 4–9

**Distinguishing characters.** Dorsoventrally compressed cyst with a typical peridinioid outline. Cyst wall is thin, with a smooth surface consisting of single-layered and light brown in colour. Two symmetrical pointed and solid tipped antapical horns are separated by a deep or shallow antapical depression. The apical horn has a flattened tip and the apical core area is thickened. Cingular margins bear low thickened ridges marking a narrow excavated, circular cingulum. An apically converging pair of similar ridges is present on the ventral surface of the epicyst. Archeopyle intercalary (2a), bell-shaped, elongated posterior-anteriorly.

**Dimensions.** Length 63–83 µm (Reid, 1977).

**Remarks.** *Lejeunecysta oliva* is distinguished from *Lejeunecysta sabrina* (Reid, 1977) Bujak, 1984 in having low thickened ridges on the cingular margins and two pairs of apically converging ridges on the epicyst. Harland (1977) considered *Lejeunecysta oliva* as having denticulate cingular margins and therefore synonymized this species with *Lejeunecysta paratenella* (Benedek, 1972) Artzner and Dörhöfer, 1978, itself considered a junior synonym of *Selenopemphix selenoides* Benedek, 1972 emend. Benedek and Sarjeant, 1981, described from the Oligocene of Germany. The latter species indeed has denticulate margins, as well as a strongly asymmetrically positioned archeopyle. However, these features are not mentioned in Reid's (1977) original description, and *Lejeunecysta oliva* was sustained as a separate and distinctive species by Turon and Londeix (1988) and Rochon et al. (1999).
**Biological affinity.** *Protoperidinium* sp., according to Rochon et al. (1999).

**Lowest stratigraphic occurrence.** Uncertain occurrences in the uppermost Miocene and Pliocene (de Vernal and Mudie, 1989, as *Lejeunecysta cf. paratenella*; de Vernal et al., 1992; Bertini et al., 1998; Londeix et al., 1999), but reliable records from the Lower Pleistocene (e.g., Combourieu-Nebout et al., 1999; McCarthy et al., 2004; Guimarães da Silva et al., 2011).

*Lejeunecysta sabrina* (Reid, 1977) Bujak, 1984

Plate 22, figs. 10–12

**Distinguishing characters.** Dorsoventrally compressed cyst with a typical peridinioid outline. Cyst wall is thin, with a microgranulate surface, single layered and light brown pigmented. Cingulum only slightly indented with delicately thickened margins, inclined and displaced circular, and deep ventral sulcus. Two more-or-less symmetrical tapering antapical horns are separated by a deep or shallow antapical depression. The tips of the antapical horns may be smoothly rounded or have sharp points, while the apical horn has a flattened tip. Apical pore area thickened. Some faint lines of thinning may occur along plate boundaries, while the surface may be ornamented with longitudinal thickenings, striations, or folds. Archeopyle intercalary (2a).

**Dimensions.** Length 58–90 µm (Reid, 1977).

**Remarks.** *Lejeunecysta sabrina* differs from *Lejeunecysta oliva* by not having a pronounced, depressed cingulum. *Lejeunecysta sabrina* differs from *Quinquecuspis concreta* (Reid, 1977) Harland, 1977 in having a thinner wall and antapical horns tapering to sharp points on some specimens.

**Biological affinity.** Some specimens of *Lejeunecysta sabrina* resemble cysts of *Protoperidinium leonis* (Pavillard, 1916) Balech, 1974. Because of its high degree of morphological variation, the cysts commonly identified as *Lejeunecysta sabrina* may represent more than one biological species (Reid, 1977).

**Lowest stratigraphic occurrence.** Lower Pleistocene (Guimarães da Silva et al., 2011).

## Genus *Protoperidinium* Bergh, 1881

**Comments.** A motile-defined genus.

See Mertens et al. (this issue) for the cysts of *Protoperidinium abei* (Paulsen, 1931) Balech, 1974 var. *rotunda* (Abé, 1936) Taylor, 1976, *Protoperidinium biconicum* (Dangeard, 1927) Balech, 1974, *Protoperidinium denticulatum* (Gran and Braarud, 1935) Balech, 1974, *Protoperidinium excentricum* (Paulsen, 1907) Balech, 1974, *Protoperidinium fukuyoi* Mertens et al., 2013, *Protoperidinium fuzhouense* Liu et al., 2015, *Protoperidinium humile* (Schiller, 1935) Balech, 1974, *Protoperidinium latissimum* (Kofoid, 1907) Balech, 1974, *Protoperidinium lewisiae* Mertens et al., 2015c, *Protoperidinium paraoblongum* Sarai et al., 2013, *Protoperidinium parthenopes* Zingone and Montresor, 1988, *Protoperidinium punctulatum* (Paulsen, 1907) Balech, 1974, *Protoperidinium quadrioblongum* Sarai et
al., 2013, *Protoperidinium steidingerae* Balech, 1979, *Protoperidinium thorianum* (Paulsen, 1905) Balech, 1974, *Protoperidinium thulesense* (Balech, 1958) Balech, 1973, and *Protoperidinium tricingulatum* (Kawami et al., 2009) Potvin et al., 2013.

**Cyst of *Protoperidinium americanum* (Gran and Braarud, 1935) Balech, 1974**

Plate 23, figs. 1–8

**Distinguishing characters.** Small to medium-sized cyst with a brown-pigmented spherical central body and a translucent, membranous loosely-appressed outer layer. Wall of central body up to about 1 µm thick consisting of a thin, solid inner layer and a thicker, closely-appressed granular outer layer. The overlying outer membrane is thin, smooth, and folded. It occasionally detaches, exposing the granular surface of the central body. The archeopyle on the central body appears to involve the separate release of the second, third and fourth apical plates, and accessory sutures may be present. There are no other indications of tabulation.

**Dimensions.** Central body diameter 34–52 µm (Lewis and Dodge, 1987; Rochon et al., 1999).

**Remarks.** The cyst of *Protoperidinium parthenopes* is similar but differs in being smaller (24–34 µm; Kawami and Matsuoka, 2009), having only narrow contact areas between the periphragm and the endophragm with a much clearer and wider separation of both layers. Kawami and Matsuoka (2009) suspected that *Protoperidinium parthenopes* cyst had been misidentified as *Protoperidinium americanum* cysts. However, *Protoperidinium parthenopes* cysts possibly do not survive palynological treatment since they are not observed in such preparation (unpublished observations by KNM).

**Biological affinity.** The cyst-theca relationship was first described by Lewis and Dodge (1987).

**Lowest stratigraphic occurrence** Upper Pleistocene (e.g., Verleye and Louwye, 2010; Hardy, 2017) and possibly Lower Pleistocene (Glasian; Powell et al., 1990).

**Cyst of *Protoperidinium nutum* (Meunier, 1919) Balech, 1974?**

Plate 23, figs. 9–10

**Distinguishing characters.** Small cyst with a brown-pigmented subspherical body and weak polar compression, ornamented by relatively long simple processes. Processes are conical at the base, solid and taper to a sharp point. The archeopyle is intercalary (2a). The cingulum is marked by two parallel rows of processes.

**Dimensions.** Width 31–48 µm, process length 10 µm (Wall and Dale, 1968; Marret and Zonneveld, 2003).
**Remarks.** Cysts of *Protoperidinium nudum* differ from *Selenopemphix quanta* (Bradford, 1975) Matsuoka, 1985 in having fewer and more slender processes which appear longer relative to the total cyst diameter. They are also smaller than *Selenopemphix quanta*, have weaker polar compression, and the processes appear more regularly spaced along the cingular margins.

**Biological affinity.** The cyst-theca relationship was first described by Wall and Dale (1968).

**Lowest stratigraphic occurrence.** Possibly in Upper Miocene sediments (offshore Angola Tortonian; Piriou, 2006, pl. 27 fig. 8 as *Selenopemphix quanta*), confirmed occurrence from the Middle (Alboran Sea; LL, unpublished observations) to Upper Pleistocene (e.g., Marret et al., 2008).

**Cyst of *Protoperidinium stellatum* (Wall in Wall and Dale, 1968) Head in Rochon et al., 1999**

Plate 23, figs. 11–14

**Distinguishing characters.** Proximate cyst with strong dorso-ventral compression. Five distinct horns of approximately equal length are present at each angle of the peragonal brown body. Each horn is hollow and relatively narrow at the base and tapers to a conspicuously solid point. Cyst wall is smooth. Archeopyle theropylic, apparently formed by an opening along the margins of plates 1a and 2a. The opercular plates remain attached to the cyst along their lateral margins.

**Dimensions.** Central body length 30–47 µm, process length 8–21 µm (Reid, 1977).

**Remarks.** The archeopyle style has seldom been documented for this species and requires confirmation. For a detailed discussion on the taxonomy and nomenclature see Head in Rochon et al. (1999).

**Biological affinity.** The cyst-theca relationship was first described by Wall and Dale (1968).

**Lowest stratigraphic occurrence.** Lower Pleistocene (e.g., Harland, 1979; Matthiessen and Brenner, 1996; McCarthy and Mudie, 1996).

**Genus *Quinquecuspis* Harland, 1977**

**Comments.** A cyst-defined genus.

**Quinquecuspis concreta (Reid, 1977) Harland, 1977**

Plate 24, figs. 1–6

**Distinguishing characters.** Large, brown, dorso-ventrally compressed cyst with a prominent apical horn and two distinct antapical horns. The antapical horns are rounded and may be irregularly thickened at their tips. The wall is thick (~0.5–1.5 µm) and the surface is smooth or roughened. In specimens from anoxic basins (e.g., Saanich Inlet, British Columbia, Canada), tabulation may be variably expressed by
discrete sutural thickenings (observations by AR and KNM). In lateral view, the cingulum is inclined at ~45° to the vertical axis of the cyst. The cingulum is well delimited and slightly excavated. The hypocyst sometimes bears faint longitudinal striations, which may be present in almost the entire surface of the cysts from anoxic environments. The sulcal area is deeply indented and may bear two depressions corresponding to flagellar scars. The archeopyle is intercalary formed by loss of plate 2a, although an adjacent apical plate (3') is often also involved and there is frequent breakage of the cyst around the archeopyle.

**Dimensions.** Length 60–80 µm (Reid, 1977); new measurements by A.R. on specimens collected from fresh surface sediments from the Gulf of Annaba, Algeria: apical–antapical length 51 (63) 75 µm (N=17), dorsal-ventral width 40 µm (N=1), left-right lateral width 53 (61) 71 µm (N=16).

**Remarks.** *Lejeunecysta sabrina* has a thinner wall and antapical horns tending to sharp points on some specimens.

**Biological affinity.** *Quinquecuspis concreta* has been linked to *Protoperidinium leonis* by Reid (1977), based on incubation experiments by Wall and Dale (1968). A similar cyst type has been described by Akselman (1987) who related this cyst to *Protoperidinium obtusum* (Karsten, 1906) Parke and Dodge, 1976. The motile stages of *Protoperidinium leonis* and *Protoperidinium obtusum* have been repeatedly confused in the literature and the cyst-theca relationship in both species needs reinvestigating.

**Lowest stratigraphic occurrence.** Upper Miocene (Brown and Downie, 1985; de Verteuil, 1996).

**Genus Selenopemphix Benedek, 1972 emend. Head, 1993, nom. cons.**

**Comments.** A cyst-defined genus.

The name *Selenopemphix* Benedek, 1972 is conserved against *Margosphaera* Nagy, 1965, nom. rej. (Fensome et al., 2016). See Mertes et al. (this issue) for *Selenopemphix tholus* (Bradford, 1975) Head, 1996, and *Selenopemphix undulata* Verleye et al., 2011.

**Selenopemphix nephroide. Benedek, 1972 emend. Bujak in Bujak et al., 1980, nom. cons.**

Plate 24, figs. 7–9

**Distinguishing characters.** Polar compressed peridinioid cyst with an ovoidal to reniform outline in polar view. Wall is single-layered with a smooth surface and brown in colour. Apical and antapical horns are low and have rounded terminations. The cingulum is wide and deeply indented, making its margins appear flange-like in polar view. The sulcus is wide, short, and similarly strongly indented, and may show two small depressions that reflect the flagellar pores. Archeopyle large and intercalary (2a), the margins of which have rounded angles; its position is slightly offset to the right of the mid-dorsal line.

**Dimensions.** Diameter 48–60 µm (Wall and Dale, 1968).
**Remarks.** This species is most often observed in polar view under the light microscope. It is distinguished from *Selenopemphix undulata* by its smooth cyst wall and the absence of undulate cingular margins (Verleye et al., 2011). The name *Selenopemphix nephroides* Benedek, 1972 is conserved against *Margosphaera velata* Nagy, 1965, nom. rej. (Fensome et al., 2016).

**Biological affinity.** *Protoperidinium subinerme* (Paulsen, 1904) Loeblich III, 1970, according to Wall and Dale (1968). However, Lewis et al. (1984) considered this species to produce smooth, spherical, brown cysts that are quite different from those observed by Wall and Dale (1968). Other studies have linked the cysts produced by *Protoperidinium subinerme* to the cyst-defined species *Selenopemphix alticincta* (Bradford, 1975) Matsuoka, 1985, described from modern sediments of the Persian Gulf (Bradford, 1975) (see Head, 1996). Therefore, disagreement exists as to whether the cysts observed in late Quaternary sediments correspond to the modern species *Selenopemphix alticincta*, to *Selenopemphix nephroides* described from the Oligocene of Germany (Benedek, 1972; Benedek and Sarjeant, 1981), or to neither species, and how these cyst forms relate to the motile-defined *Protoperidinium subinerme*.

**Lowest stratigraphic occurrence.** Lower Eocene (e.g., De Coninck 1971; Heilmann-Clausen and Costa, 1989). Sparse and unillustrated older records are not considered to represent confirmed occurrences.

### *Selenopemphix quanta* (Bradford, 1975) Matsuoka, 1985

Plate 25, figs. 1–8

**Distinguishing characters.** Polar compressed peridinioid cyst with a subcircular to slightly reniform outline in polar view. The smooth wall is slightly medium brown. Sturdy and rigid processes taper to sharp or blunt points and become solidly elongated. Processes occur along both cingular margins and are distributed with variable density on the epi- and hypocyst, but not in the sulcus. Two flagellar scars may be visible within the sulcus. Archeopyle elongated in outline, formed by loss of the second anterior intercalary plate (2a); its margin has rounded angles and its position is nearly symmetrical to slightly offset to the right of the mid-ventral line.

**Dimensions.** Central body width 40–83 µm, process length 10–16 µm (Rochon et al., 1999).

**Remarks.** Based on the wide range in central body size and in process length and distribution, Head (1996) and Rochon et al. (1999) suggested that more than one biological species might be represented by the cysts commonly identified as *Selenopemphix quanta* (see also the work by Kobayashi and Matsuoka, 1984). While often grouped together, cysts of *Protoperidinium nudum* differ from *Selenopemphix quanta* (sensu stricto) in their smaller size, weaker polar compression, and in having relatively longer processes that may be arranged in more orderly rows.

**Biological affinity.** *Protoperidinium conicum* (Gran, 1900) Balech, 1974, according to Kobayashi and Matsuoka (1984), among others.

**Lowest stratigraphic occurrence.** Upper Oligocene of northwest Italy (Powell, 1986; Zevenboom, 1996; Brinkhuis et al., 2003).
**Genus *Trinovantedinium* Reid, 1977 emend. de Verteuil and Norris, 1992**

**Comments.** A cyst-defined genus.

*Trinovantedinium applanatum* (Bradford, 1977 [April]) Bujak and Davies, 1983 is a taxonomic senior synonym of *Trinovantedinium capitatum* Reid, 1977 [November], although the type of the genus *Trinovantedinium* remains the holotype of *Trinovantedinium capitatum*, as noted by Williams et al. (2017).

See Mertens et al. (this issue) for *Trinovantedinium pallidifulvum* Matsuoka, 1987.

*Trinovantedinium applanatum* (Bradford, 1977) Bujak and Davies, 1983

Plate 25, figs. 9–12

**Distinguishing characters.** Relatively large dorsoventrally compressed cyst with an angular pentagonal to rounded peridinioid outline. The wall is single-layered and pale to hyaline. A short solid protuberance may be present on the apical horn. The processes are short and solid with acuminate or, more commonly, minutely expanded tips. They are aligned along the cingular margins and have an irregular intratabular distribution elsewhere on the cyst, except for the wide sulcal area where ornamentation is lacking. A flagellate scar may be present. Archopore intercalary (2a), subrectangular in outline and may be wider than high.

**Dimensions.** Length 54–96 µm, process length 5–7 µm (Reid, 1977; Rochon et al., 1999).

**Remarks.** *Trinovantedinium applanatum* is the only known living protoperidiniacean cyst type that lacks a pigmented wall. This, in addition to its larger and more elongate body and longer processes, distinguishes this species from *Trinovantedinium pallidifulvum* (see also Mertens et al., 2016 and this issue).

**Biological affinity.** *Protoperidinium shanghaiense* Gu et al., 2015, according to Gu et al. (2015). The cyst has erroneously been referred to *Protoperidinium pentagonum* (Gu et al., 2015).

**Lowest stratigraphic occurrence.** Williams et al. (2004) considered the lowest appearance of *Trinovantedinium applanatum* as marking the base of the Miocene. However, Miocene specimens are often labelled as "cf." (e.g., Lenoir and Hart 1986; Manum et al., 1989; de Verteuil and Norris, 1992; Zevenboom, 1997; Londeix and Jan du Chêne, 1998), and when depicted (e.g., Edwards, 1986, 1990; Kumar and Saxena, 1997; El Beialy and Ali, 2002; Soliman et al., 2012) they appear somewhat different from Holocene reference specimens (Bradford, 1977; Reid, 1977). It is therefore difficult to confidently identify the lowest common occurrence level of *Trinovantedinium applanatum*, which might be as high as Pliocene or lowermost Quaternary.

**Genus *Votadinium* Reid, 1977 emend. Gurdebeke et al., 2019b**

**Comments.** A cyst-defined genus.
**Votadinium calvum Reid, 1977**

Plate 26, figs. 1–3

**Distinguishing characters.** Dorsoventrally compressed cyst with a strongly rounded peridinioid outline. The wall is thin, dark brown, and has a smooth to microgranular surface. The apical horn is strongly reduced, represented by a light swelling such that the 2a intercalary archeopyle extends over the apex. The rounded, equally-developed antapical horns are separated by a shallow antapical depression. The wall is unthickened at the horns.

**Dimensions.** Length 54–72 µm (Reid, 1977).

**Biological affinity.** *Votadinium calvum* as described by Reid (1977) corresponds to just one of several cyst types illustrated and linked to *Protoperidinium oblongum* by Wall and Dale (1968). The cyst-theca relationships of the *Protoperidinium oblongum* complex were re-studied by Sarai et al. (2013) who linked the morphotype that conforms to *Votadinium calvum* as described by Reid (1977) (i.e., the specimen in pl. 1, fig. 25–28 of Wall and Dale, 1968) with *Protoperidinium claudicans* (Dangeard, 1927) Balech, 1974.

**Stratigraphic range.** Upper Pliocene (Mudie, 1987). Isolated observations from the Lower Miocene by Londeix and Jan du Chêne (1998, not illustrated) appear to conform with the morphology of Quaternary specimens (unpublished observations by LL).

**Votadinium spinosum Reid, 1977**

Plate 26, fig. 4–5, 7–8

**Distinguishing characters.** Dorsoventrally compressed brown cyst with a rounded peridinioid outline and two antapical horns which are separated by a shallow antapical depression. Central body wall thin, with smooth surface, and covered by numerous short solid spines of equal length which are usually curved and are irregularly distributed over the entire cyst. The archeopyle, formed by loss of intercalary plate 2a, extends over the apex.

**Dimensions.** Length 49–54 µm, process length 3–7 µm (Reid, 1977).

**Biological affinity.** *Protoperidinium claudicans* (Paulsen, 1907) Balech, 1974, according to Dale (1983), among others.

**Lowest stratigraphic occurrence.** Lower Pleistocene (Bujak and Matsuoka, 1986; Powell et al., 1990).

**Genus Xandarodinium Reid, 1977**

**Comments.** A cyst-defined genus.
**Xandarodinium xanthum Reid, 1977**

Plate 26, figs. 6, 9–12

**Distinguishing characters.** Light brown pigmented cyst with a concave ventral area and convex dorsal area, smooth wall surface and varied processes. Processes are unusual in that the central body cavity extends far into the process itself. Processes can be simple, or complex flanges terminating in simple solid spines or multifurcate tips. A wide range of process morphologies occurs on the same cyst. Ventral and anterior dorsal surfaces are devoid of processes. Dorsal processes are intratabular, along the equatorial axis, reflecting the cingulum and intercalary plates. Processes are thicker and darker in colour at their distal ends, this occurring abruptly at the level where the central body cavity ends. An apical and two indistinct antapical horns may be discerned. Archeopyle formed by loss of a single, apparently intercalary plate. The operculum lacks processes.

**Dimensions.** Cyst body size 46 x 46 to 46 x 63 µm, process length 2–19 µm (Reid, 1977).

**Biological affinity.** *Protoperidinium divaricatum* (Meunier, 1914; Parke and Dodge, 1976, according to Matsuoka et al. (1982) and Lewis et al. (1984), among others).

**Lowest stratigraphic occurrence.** Records from the Upper Miocene of the Labrador Sea (Head et al., 1989c), Middle and Upper Miocene of offshore eastern U.S.A. (de Verteuil, 1996, as *Xandarodinium xanthum* sensu Head et al., 1989c), Lower and Middle Miocene of Egypt (as *Xandarodinium* sp. 1), and Lower Pliocene of India (Kumar and Saxena, 1997) are all considered to represent *Xandarodinium xanthum*. *Artemisiocysta distendata* Mertens et al., 2008, p. 129, pl. 10, figs. 7–9 from the upper Lower Miocene? and/or Lower Middle Miocene of Indonesia is here considered a taxonomic junior synonym of *Xandarodinium xanthum*. We therefore accept an upper Lower Miocene or Lower Middle Miocene range base for this species.

Subfamily UNCERTAIN

**Genus Echinidinium Zonneveld, 1997 ex Head et al., 2001**

**Comments.** A cyst-defined genus.

See Mertens et al. (this issue) for *Echinidinium aculeatum* Zonneveld, 1997 ex Mertens et al., this issue, *Echinidinium bispiniformum* Zonneveld, 1997 ex Head et al., 2003, *Echinidinium delicatum* Zonneveld, 1997 ex Head et al., 2003, *Echinidinium granulatum* Zonneveld, 1997 ex Head et al., 2001, *Echinidinium transparantum* Zonneveld, 1997 ex Mertens et al., this issue, and *Echinidinium zonneveldiae* Head, 2003.

**Echinidinium karaense Head et al., 2001**
Plate 27, figs. 1–5

**Distinguishing characters.** Brown cyst having a spheroidal central body with a smooth wall ornamented with short (≤3 µm) coni or spinules scattered between numerous processes. The processes are nontabular, robust with a variably but fairly wide base, and conical to tapering. They are apiculocavate (i.e., cavation only at the base) to mostly hollow and solid distally, with the degree of pericoel development varying between processes of an individual cyst. Process tips are either acuminate or minutely expanded and flared, usually both types being present on the same cyst. On processes with minutely expanded tips, aculeae rarely exceeding 1.0 µm and directed away from the cyst wall are often discerned. Archeopyle theropylic, opening by means of a long, nearly straight split, presumably along plate sutures as suggested by slight angulations that are sometimes observed along its course.

**Dimensions.** Central body diameter 22–45 µm, process length 3–11 µm (Hadi et al., 2013).

**Biological affinity.** Unknown, but phylogenetic analyses by Potvin et al. (2018) suggested that this species is placed within the *Monovela* clade of the genus *Protoperidinium* (Matsuoka and Kawami, 2013).

**Lowest stratigraphic occurrence.** Upper Pleistocene (Matthiessen and Knies, 2001; Grøsfjeld et al., 2006).

## Genus uncertain

*"Cysts of Polykrikos? sp. of Kunz-Pirrung 1952 (ibid. plate 3, figs. 4–13)"*

**Remarks.** Molecular characterization of different morphotypes from this group of cysts reveals a position in the *Monovela* clade of the Protoperidiniaceae, and not within the Gymnodiniales (Potvin et al., 2018). Since no alternative genus or species names have been proposed for these morphotypes, they are described in detail under the genus *Polykrikos* (Gymnodiniales).

Family THORACOSPHAERACEAE Schiller, 1930 emend. Tangen in Tangen et al., 1982

**Remarks.** There is ongoing discussion of the higher taxonomic hierarchy of calcareous dinoflagellates that belong to the genera *Pentapharsodinium*, *Ensiculifera* and *Scrippsiella*. Traditionally, the suprageneric classification of Fensome et al. (1993) has been followed, based on earlier work by Tangen et al. (1982), placing these genera within two separate taxonomic units, the order Thoracosphaerales, and the subfamily Calciodinelloideae within the family Peridiniaceae of the order Peridiniales. However, based on molecular phylogenetic studies suggesting that calcareous dinoflagellates belong to a single monophyletic group, Elbrächter et al. (2008) proposed their placement within the single family Thoracosphaeraceae of the order Peridiniales, a classification that has found further support from ensuing molecular studies (e.g., Gottschling et al., 2012) and is followed here. However, others have retained the order Thoracosphaerales (e.g., Moestrup and Calado, 2018).
**Genus *Pentapharsodinium Indelicato and Loeblich III, 1986* emend. Montresor et al., 1993

**Comments.** The genus *Pentapharsodinium* includes species that produce cysts with calcareous walls, and those that produce cysts with exclusively organic walls. *Pentapharsodinium tyrrhenicum* Montresor et al., 1993, described from surface sediments of the Mediterranean Sea (Montresor et al., 1993), produces a cyst with a calcareous outer layer supported by an organic membrane. The cyst was also described as the fossil *Calcicarpinum bivalvum* Versteegh, 1993 from the Upper Pleistocene of the Mediterranean Sea (Versteegh, 1993; Montresor et al., 1994). After dissolution of the outer calcareous layer by acid treatment, as required for palynological processing, the organic membrane constitutes a fairly featureless, thin-walled, smooth and yellowish round palynomorph. *Pentapharsodinium jinhaense* Li et al., 2015b, described from surface waters off South Korea (Li et al., 2015b), also produces a calcareous cyst which, when the outer calcareous layer is dissolved, leaves a spherical to oval smooth organic-walled cyst with observable theropylic intercalary archeopyle, not readily distinguishable from the organic-walled linings of acidified cysts of *Scrippsiella acuminata* Ehrenberg, 1836) Kretschmann et al., 2015 (Li et al., 2015b). *Pentapharsodinium dalei* produces a cyst with an exclusively organic wall. Because this cyst has clearly distinguishable morphological features, it is discussed in more detail below.

**Cyst of *Pentapharsodinium dalei* Indelicato and Loeblich III, 1986**

Plate 27, figs. 6–11

**Distinguishing characters.** Small colourless chorate species ornamented with solid nontabular processes. The central body is sub-spherical and has a smooth surface. The wall is thin and comprises two closely appressed layers. Tabulation is absent. The processes are straight or may branch at any point along their length, with different types often present on a single cyst. Processes are often minutely branched or otherwise expanded at their tips. Process bases may be expanded, and some may be joined to adjacent bases by low septa, resulting in a partial reticulation over the surface. The archeopyle is chasmic, represented by a slit-like rupture.

**Dimensions.** Cyst diameter 19–66 µm, process length 1–8 µm (Dale, 1977, as *Peridinium faeroense*); new measurements by AR on specimens collected from fresh surface sediments in the Gulf of St. Lawrence: Cyst diameter 21 (23.5) 26 µm (N=14), process length 2.7 (4.1) 5.7 µm (N=141 on 14 specimens), septa height 0.2 (0.6) 1.1 µm (N=50 on 14 specimens).

**Remarks.** *Ensiculifera imariense* Kobayashi and Matsuoka, 1995, described from western Japan, has vegetative cells that are distinct from *Pentapharsodinium dalei* but produces cysts that differ only in having wider processes (Kobayashi and Matsuoka, 1995). Given that the differences are subtle, both cyst morphotypes have been grouped together in a number of studies (e.g., Zonneveld et al., 2013; Zonneveld and Pospelova, 2015).

**Lowest stratigraphic occurrence.** Upper Miocene and Lower Pliocene of the Norwegian Sea (Beck, 2013; De Schepper et al., 2015, 2017); and Lower Pliocene of the Mediterranean Sea (Popescu et al., 2015), North Sea basin (Louwye et al., 2004), and off Western Tasmania (Brinkhuis et al., 2003).
**Genus *Scrippsiella* Balech, 1959 ex Loeblich III, 1965**

**Comments.** A motile-defined genus.

The calcareous cyst of *Scrippsiella crystallina* Lewis, 1991 ex Head, 1996 is ovoidal with an outer covering of blocky crystals, and when these are removed by acid the underlying thin organic wall is revealed to have a faintly reticulated surface (Head et al., 2006). Such organic linings occur in palynological preparations at least back to the Miocene (e.g., Jiménez-Moreno et al., 2006, pl. 2, figs. 6–8), but they are thin walled and not easily recognized. Following acidification, the calcareous cyst of *Scrippsiella acuminata* (Ehrenberg, 1836) Kretschmann et al., 2015 — the heterotypic senior synonym of *Scrippsiella trochoidea* (Stein, 1883) Loeblich III, 1976) — leaves an ovoidal organic membrane with an almost smooth wall bearing slightly raised imprints of some of the processes (Mudie et al., 2017).

**Cyst of *Scrippsiella trifida* Lewis, 1991 ex Head, 1996**

Plate 27, figs. 12–15

**Distinguishing characters.** Ovoidal, transparent cysts, with inner smooth organic layer and an outer undulating organic layer that reflects the shape of the underlying large calcareous processes which are not present in palynologically treated samples. *Arthropleyle theropylic, mesoepi cystal* (involving plates 2'-4' and 1a-3a), with zigzag principal suture. *Opérculum* usually adnate, remaining ventrally attached.

**Dimensions.** Central body length 29–41 µm. process length 3–5 µm (Head et al., 2006).

**Remarks.** This species was referred to "*C. Alexandrium tamarense*-type cysts" in Rochon et al. (1999), and to the cysts of both *Alexandrium excavatum* (Braarud, 1945) Balech and Tangen, 1985 and *Alexandrium tamarense* (Lebour, 1921) Balech, 1985 in the earlier literature (see Head et al., 2006 for discussion).

**Biological affinity.** *Scrippsiella trifida* according to Lewis (1991) and Head et al. (2006).

**Lowest stratigraphic occurrence.** Pliocene of Belgium (as "cf. *Alexandrium tamarense*-type cysts of Rochon et al. (1999)" in Louwye et al., 2004); upper Lower Pleistocene (Balota, 2018).

**Acknowledgments**

We thank Pieter R. Gurdebeke for sharing his photographs of the holotype of *Lejeunecysta sabrina*. MJH, AL and VP acknowledge support from their respective Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants. SDS acknowledges financial support from Research Council of Norway grant 268062. We are most grateful to two anonymous reviewers for their helpful comments on the manuscript, and Editor-In-Chief Richard Jordan for his feedback and efficient handling of this and all other contributions to this special issue.
Plate Captions

**Plate 1** 1–6. Cyst of *Polykrikos kofoidii*. 1–2. High focus and optical section of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 3–4. High focus and optical section of specimen from the eastern Pacific Ocean. 5–6. Optical section and low focus of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 7–9. Cyst of *Polykrikos schwartzii*. 7. High focus of specimen from the eastern Pacific Ocean. 8. Optical section of specimen from the eastern Pacific Ocean. 9. Composite image of high and mid-focus of specimen from the eastern Pacific Ocean. 10–11. Cyst of *Polykrikos*? sp. of Kunz-Pirrung (1998) – Arctic morphotype (from northern Baffin Bay, core AMD16-117Q). 12. Cyst of *Polykrikos*? sp. of Kunz-Pirrung (1998) = "*Polykrikos quadratus*", with reduced reticulation (from northern Baffin Bay, core AMD16-117Q). Images 1–2, 5–6, 10–12 by NVN, 3–4, 7–9 by VP. All scale bars = 10 µm.

**Plate 2** 1–3. *Tuberculodinium vancampoae*, specimen from 1. the Gulf of Mexico, and 2–3. eastern Pacific Ocean at different focal depths. 4–8. *Polysphaeridium zoharyi* (from the Gulf of Mexico). 4–6. High focus and optical section at two slightly different focal depths, polar view. 7–8. High and low focus, showing the typical preservation as half cysts following excystment. 9–12. *Lingulodinium machaerophorum*. 9. Specimen with short processes and bulbous process terminations from the Marmara Sea (core MAR02-45P). 10. Specimen with short processes from Black Sea surface sediments (station SH4, Mudie et al., 2017). 11–12. Specimen with relatively short processes from the SW Black Sea (core GeoB7625-2). Images 1, 4–8 by AL, 2–3 by VP, 9–12 by KNM. All scale bars = 10 µm.

**Plate 3** 1–3. *Lingulodinium machaerophorum*, high to low focus of specimen from the Labrador Sea (core GS16-204-22 CC-A). 4–15. *Operculodinium centripum*. 4–5. Morphotype with short processes and with cell content from the Arctic Ocean. 6. Morphotype with short processes from Saanich Inlet surface sediment. 7, 11. Arctic morphotype with typical slender and sparsely distributed processes from Prince of Wales Strait (Canadian Arctic Archipelago) surface sediments. 8–10. Different focal depths of a different specimen of the Arctic morphotype from the same locality. 12–13. Another specimen of the Arctic morphotype from the same locality. 14–15. Specimen of the *cezare* morphotype showing the incomplete development of sparsely distributed processes (from off Portugal). Images 1–3 by NVN, 4–5 by VP, 6, 14–15 by KNM, 7–13 by AL. All scale bars = 10 µm.

**Plate 4** 1–9. *Operculodinium centripum*. Specimen from 1. Effingham Inlet surface sediment, and 2. from off Portugal. 3. Optical section of specimen with cell content and relatively long processes from the Arctic Ocean. 4–5. High and mid focus, dorso-lateral view, of specimen from off Portugal. 6, 9. Specimen with cell content from the eastern Pacific Ocean. 7–8. Specimen with cell content having a granular surface and sturdy processes with elaborately capitate distal terminations (from the eastern Pacific Ocean). 10–12. *Operculodinium israelianum*, high to low focus of specimen from the Gulf of Mexico. Images 1–2, 4–5 by KNM, 3, 6–9 by VP, 10–12 by AL. All scale bars = 10 µm.

**Plate 5** 1–4. *Ataxiodinium choane*. 1–3. High to low focus of specimen from the Baltic Sea (core KSK12-01D). 4. Specimen with cell content cultured from Kattegat surface sediments. 5–8. *Bitectatodinium? spongium*, high and mid focus views of two specimens from surface sediments of the Gulf of Tehuantepec, off western Mexico. 9–12: *Bitectatodinium tepikiense*. 9. High focus showing archeopyle (from the Mediterranean Sea, core ODP-976). 10–12. High to low focus, ventral view, of specimen from the Iceland Plateau (core DANA12-11/2-GC01). Images 1–3, 10–12 by NVN, 4–9 by KNM. All scale bars = 10 µm.
**Plate 6** 1–8. *Impagidinium aculeatum*. 1–3. High to low focus, dorsal view, of specimen from the Labrador Sea (core GS16-204-22 CC-A). 4, 8. High and low focus, dorso-apical view, of a different specimen from the same locality. 5–7. High to low focus, dorsal view, of specimen from the Gulf of Mexico. 9–14. *Impagidinium pallidum*. 9–11. High to low focus of specimen from northern Baffin Bay (core AMD16-117Q). 12–14. High to low focus of specimen from the Baltic Sea (core KSK12-01D). Images 1–4, 8–14 by NVN, 5–7 by AL. All scale bars = 10 µm.

**Plate 7** 1–3. *Impagidinium pallidum*, high to low focus view of a specimen cultured from surface sediments of Gibbs Fjord, NE Baffin Island. 4–9. *Impagidinium paradoxum*. 4–6. High to low focus, ventral view, of specimen from the Labrador Sea (core GS16-204-22 CC-A). 7–9. High to low focus, dorsal view, of specimen from western Mediterranean Sea surface sediments (core CO-82-3 B19). 10–12. *Impagidinium patulum*, high to low focus, lateral view, of specimen from the Labrador Sea (core GS16-204-22 CC-A). Images 1–3, 7–9 by KNM, 4–6, 10–12 by NVN. All scale bars = 10 µm.

**Plate 8** 1–3. *Impagidinium patulum*, high to low focus, lateral view, of specimen from surface sediments of the central Mediterranean Sea (station 77B-1, Elshanawany et al., 2010). 4–7. *Impagidinium plicatum*, different focal depths of specimen from the Gulf of Mexico. 8–13. *Impagidinium sphaericum*. 8–10. High to low focus, oblique dorso-lateral view, of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 11–13. High to low focus, ventral view, of specimen from the Labrador Sea (core GS16-204-22 CC-A). Images 1–3 by KNM, 4–7 by AL, 8–13 by NVN. All scale bars = 10 µm.

**Plate 9** 1–6. *Impagidinium sphaericum*. 1–3. High to low focus, dorso-antapical view, of specimen from the Iceland Plateau (core DANA12-11/2-GC-1). 4–7. High to low focus, oblique left-lateral view, of a different specimen from the same locality. 7–9. *Impagidinium strialatum*, high to low focus of specimen from the Labrador Sea (core GS16-204-22 CC-A). 10–12. *Nematosphaeropsis labyrinthus*, high to low focus of specimen from western Mediterranean Sea surface sediments (core CO-82-3 B19). Images 1–9 by NVN, 10–12 by KNM. All scale bars = 10 µm.

**Plate 10** 1–5. *Nematosphaeropsis labyrinthus*. 1–3. Specimen from the Labrador Sea (core GS16-204-22 CC-A). (1) Optical section, (2) internal view of the right-lateral cyst surface, and (3) low focus view of the process terminations with trabecule. 4–5. Specimen from the eastern Pacific Ocean. 6–12. *Spiniferites belerius*. 6–9. High to low focus, ventral view, of specimen from the Dee Estuary (U.K.). 10–12. High focus and optical section at two slightly different focal depths of a different specimen from the same locality. Images 1–3 by NVN, 4–5 by VP, 6–12 by KNM. All scale bars = 10 µm.

**Plate 11** 1–5. *Spiniferites bentorii*. 1–3. High to low focus of specimen with long processes from the Mediterranean Sea (core MS21 pc643-644). 4–5. Specimen with reduced processes from the eastern Pacific Ocean. 6–12: *Spiniferites bulloideus*. 6–9. High to low focus, dorsal view, of specimen from the Labrador Sea (core GS16-204-22 CC-A). 10–12. High to low focus, dorsal view, of specimen from Black Sea surface sediments (BC53, Mudie et al., 2017). Images 1–3, 10–12 by KNM, 4–5 by VP, 6–9 by NVN. All scale bars = 10 µm.

**Plate 12** 1–6. *Spiniferites delicatus*, specimen from surface sediments from the Mediterranean Sea observed under different angles. 1–3. High to low focus, antapical view. 4. Dorsal view. 5–6. High and mid-focus, ventral view. 7–10. *Spiniferites elongatus*, high to low focus, lateral view, of specimen with wide antapical processes from northern Baffin Bay (core AMD16-117Q). Images 1–6 by AR, 7–10 by NVN. All scale bars = 10 µm.
**Plate 13** 1–12. *Spiniferites elongatus*, specimens from the Iceland Plateau (core DANA12-11/2-GC01). 1–5. High to low focus, ventral view. 6–9. High to low focus, oblique antapical view, with (6) showing one of the distally open and hollow antapical processes. 10–12. Membranous specimen, high to low focus, lateral view. All images by NVN. All scale bars = 10 µm.

**Plate 14** 1–3. *Spiniferites hyperacanthus*, high to low focus, ventral view, of specimen from the Red Sea (core sample va01-200p). 4–10. *Spiniferites lazus*. 4–6. High to low focus of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 7–8. Specimen from the Iberian margin (IODP Leg 339 Site 1385, Hole D, D10H4_08-09). 9–10. High and mid-focus of specimen from western Mediterranean Sea surface sediments (core CO-82-3 B19). Images 1–3 and 9–10 by KNM, 4–6 by NVN, 7–8 by FE/Marie-Camille Gasparotto. All scale bars = 10 µm.

**Plate 15** 1–9. *Spiniferites membranaceus*. 1–3. High to low focus, dorsal view, of specimen from off Portugal (core PO287-18B, Ribeiro et al., 2016). 3–7. High to low focus, ventral view, of a different specimen from offshore Portugal (core PO287-39B, Ribeiro et al., 2016). 8. Specimen from the Iberian margin (IODP Leg 339 Site 1385, Hole D, D10H3_138-139). 9. A different specimen from the same locality (Hole D, D10H4_16-17). Images 1–7 by KNM, 8–9 by FE. All scale bars = 10µm.

**Plate 16** 1–6. *Spiniferites mirabilis*. 1–3. High to low focus, dorsal view, of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 4–6. High to low focus, ventral view, of specimen from Black Sea surface sediments (station SH4; specimen also illustrated in Mudie et al., 2017). 7–14. *Spiniferites pachydermus*. 7–8. High and low focus, lateral view, of specimen from surface sediments in Izmir Bay, eastern Mediterranean Sea. 9–11. High to low focus, dorsal view, of a different specimen from the same locality. 12–14. High focus and optical section at two slightly different focal depths, lateral view, of a specimen with cell content from the same locality. Images 1–3 by NVN, 4–14 by KNM. All scale bars = 10 µm.

**Plate 17** 1–9. *Spiniferites ramosus*. 1–2. Specimen from the eastern Pacific Ocean. 3–6. High to low focus, dorso-lateral view, of specimen from the Labrador Sea (core GS16-204-22 CC-A). 7–9. High to low focus, ventral view, of a different specimen from the same locality. Images 1–2 by VP, 3–9 by NVN. All scale bars = 10 µm.

**Plate 18** 1–6. *Atlanticostrix striationculum*, from the Middle Pleistocene of central North Atlantic (IODP Hole U1313A) (reproduced from Head and Mantilla-Duran, this issue). 1–3. High to low focus, dorsal view, of the holotype. 4–6. High to low focus, antapical view, with (5) the operculum inside the cyst. 7–14. *Pyxidinopsis reticulata*. 7–8. High and mid-focus of specimen from the Labrador Sea (core GS16-204-22 CC-A). 9–10. Dorso-lateral view and optical section of specimen from western Mediterranean Sea surface sediments (core CO-82-3 B19). 11. Specimen from the eastern Pacific Ocean. 12–14. Three different specimens of the Okhotsk morphotype, from the Okhotsk Sea (reproduced from Bonnet et al., 2012). Images 1-6 by MJH, 7-8 by NVN, 9-10 by KNM, 11 by VP, 12-14 by Sophie Bonnet. All scale bars = 10 µm.

**Plate 19** 1. *Brigantedinium cariacoense* (from the Iceland Plateau, core DANA12-11/2-GC01). 2–7. *Brigantedinium simplex*. 2. Specimen with a slightly granular surface from the eastern Pacific Ocean. 3. Specimen with a slightly granular surface from northern Baffin Bay. 4–6. High to low focus of specimen with a coarsely granular surface from the Iceland Plateau (core DANA12-11/2-GC01), showing (4) the archeopyle with the loosely attached operculum still in place and (6) flagellar scars and delicate outline of the cingulum. 7. Specimen with smooth surface from the Iceland Plateau (core DANA12-11/2-GC01).
8–9. *Islandinium brevispinosum*, high and mid-focus of specimen with cell content from the Atlantic Ocean. 10–12. *Islandinium? cezare*, high to low focus of specimen from northern Baffin Bay (core AMD16-117Q). Images 1, 4–7, 10–12 by NVN, 2, 8–9 by VP, 3 by AL. All scale bars = 10 µm.

**Plate 20** 1–6. *Islandinium? cezare*. 1–3. High to low focus of specimen with relatively long processes from northern Baffin Bay (core AMD16-117Q). 4–5. A different specimen of *Islandinium? cezare* with relatively long processes from the same locality: (4) optical section and (5) low focus on the archeopyle. Also note the delicately granular cyst surface. 6. Specimen with very long processes from the same locality. 7–12. *Islandinium minutum* subsp. *minutum*. 7–9. High to low focus of specimen from northern Baffin Bay (core AMD16-117Q). 10–12. High to low focus of a different specimen from the same locality. All images by NVN. All scale bars = 10 µm.

**Plate 21** 1–3. *Islandinium minutum* subsp. *minutum*, high focus and optical section at two slightly different focal depths of specimen from northern Baffin Bay. 4–5. *Islandinium minutum* subsp. *minutum*, (4) high focal view of the archeopyle and (5) optical section of specimen with cell content from the Arctic Ocean. 6–8. *Islandinium minutum* subsp. *minutum* with relatively short processes (left) and *Islandinium minutum* subsp. *barbatum* with very long processes (right). Note the presence of minute barbs on and at the distal ends of processes of the subsp. *barbatum* specimen. High to low focus (from northern Baffin Bay, core AMD16-117Q). 9–11. *Islandinium minutum* subsp. *barbatum*, high focus and optical section at two slightly different focal depths, of specimen with very long processes from the same locality. Images 1–3 by AL, 4–5 by VP, 6–11 by NVN. All scale bars = 10 µm.

**Plate 22** 1–3. *Islandinium minutum* subsp. *barbatum*, high to low focus of specimen with very long processes from northern Baffin Bay (core AMD16-117Q). 4–9. *Lejeunecysta oliva*. 4–7. Different views of specimen cultured from Menai Strait (U.K.) surface sediments: (4) dorsal view, (5) oblique dorso-antapical view, (6) ventral view and (7) left-lateral view. 8–9. Specimen from offshore Portugal. 10–12. *Lejeunecysta sabrina*, new micrographs of holotype. Images 1–3 by NVN, 4–9 by KNM, 10–12 by Pieter R. Gurdebeke. All scale bars = 10 µm.

**Plate 23** 1–8. Cyst of *Protoperidinium americanum*. 1–3. High to low focus of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 4, 8. Optical section and low focal view showing the archeopyle of specimen from the eastern Pacific Ocean. 5–7. High to low focus of specimen from the Iceland Plateau (core DANA12-11/2-GC01) that has lost its outer membrane, exposing the granular outer surface of the cyst wall. 9–10. Cyst of *Protoperidinium nudum*, high and mid-focus of specimen from the same locality. 11–14. Cyst of *Protoperidinium stellatum*. 11. Dorso-ventral view of specimen from the Pacific Ocean. 12. Dorso-ventral view of specimen from the Dee Estuary (U.K.). 13–14. High and low focus, dorso-ventral view, of specimen from Omura Bay (Japan). Images 1–10 by NVN, 11 by VP, 12–14 by KNM. All scale bars = 10 µm.

**Plate 24** 1–6. *Quinquecuspis concreta*. 1–3. High to low focus, oblique antapical view, of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 4–5. Specimen from the same locality in dorsal view, showing (4) the archeopyle in high focus and (5) the sulcus with flagellar scar in low focus. 6. Specimen from the Pacific Ocean. 7–9. *Selenopemphix nephroides*, high to low focus, apical view, of specimen from the Iceland Plateau (core DANA12-11/2-GC01). All images by NVN except 6 by VP. All scale bars = 10 µm.

**Plate 25** 1–8. *Selenopemphix quanta*. 1–2. Oblique apical view of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 3. Specimen from the Pacific Ocean. 4–6. High to low focus of a different specimen from the same locality. 7–8. Specimen with somewhat less robust process bases from the
same locality. 9–12. *Trinovantedinium applanatum*. 9. Ventral view of specimen from the Pacific Ocean. 10–12. High to low focus, ventral view, of specimen from the Iceland Plateau (core DANA12-11/2-GC01). All images by NVN except 3 and 9 by VP. All scale bars = 10 µm.

**Plate 26** 1–3. *Votadinium calvum*, high to low focus of specimen from the Baltic Sea (core KSK12-01D). 4–5. *Votadinium spinosum*, high and low focus of specimen with cell content from Patricia Bay (Saanich Inlet) surface sediment. 7–8. *Votadinium spinosum*, high focus and optical section of a different specimen with cell content from the same locality. 6, 9. *Xandarodium xanthum*, high and low focus, equatorial view, of specimen from the Last Interglacial (Late Pleistocene) of the Baltic Sea (specimen also illustrated in Head et al., 2005, fig. 12a,b). 10–12. *Xandarodinium xanthum*, high to low focus of specimen from the Dee Estuary (U.K.) surface sediment. Images 1–3 by NVN, 6, 9 by MJH, 4–5, 7–8, and 10–12 by KNM. All scale bars = 10 µm.

**Plate 27** 1–5. *Echinidinium karaense*. 1–3. High to low focus of specimen with cell content from Independence Fjord (NE Greenland) surface sediments (Limoges et al., 2008). 4–5. High focus and optical section of another specimen with cell content from the same locality, with the arrow in (5) indicating the clearly expanded and flared tip of one of the process. 6–11. Cyst of *Pentapharsodinium dalei*. 6–7. High and mid-focus of specimen from northern Baffin Bay. 8. Specimen with cell content from the eastern Pacific Ocean. 9–11. High to low focus of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 12–15. Cyst of *Scrippsiella trifida*. 12–13. High and mid-focus of specimen from the Iceland Plateau (core DANA12-11/2-GC01). 14–15. Optical section and low focus of a different specimen from the same locality. Images 1–7 by AL, 8 by VP, 9–15 by NVN. All scale bars = 10 µm.

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