Mayrocaris undetermined
Creators: name: Laville, Thomas
name: Forel, Marie-Béatrice
name: Charbonnier, Sylvain
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Dollocarididae
Mayrocaris
Mayrocaris undetermined

description: Mayrocaris sp.
Fig. 10
Dollocaris sp. – Secrétan & Riou 1983: text-fig. 14c.
Material examined
FRANCE • 11 specs; La Boissine, La Voulte-sur-Rhône, Ardèche, France; Callovian, Middle Jurassic; MNHN.F. A29366, A84014 to A84022, R50964.
Measurements
See Table 2.
Description
Shield morphology
Sub-trapezoidal shield in lateral view with an anterior margin formed by a weakly developed optic notch bent in its central part, a sharp antero-dorsal corner, a slightly convex dorsal midline ascending until a carina located in the last third of the margin. (Fig. 10); dorsal midline with small serrations in the anterior part of the midline; posterior margin consisting of a notch delimited dorsally by a postero-dorsal corner expressed as a spine with a rounded tip and ventrally by a rounded postero-ventral corner; ventral margin divided into a steep posterior half descending antero-ventrally and an anterior one slightly ascending antero-dorsally and bearing a pronounced subquadratic notch; ventral margin ending anteriorly as a rounded antero-ventral corner. Rim of all free margins delimiting a marginal fold.
Shield macro-ornamentation
Presence of a medio-lateral carina in the central part of the shield, above the gills (Fig. 10A–D). One rounded pore, formed by a canal-like structure, sitting close to the anterior end of the carina (Fig. 11A–D).
Sensory structures
Oval, stalked compound eyes protruding from the optic notch and occupying all of it (Fig. 10).
Cephalic appendages
One antenniform structure protruding from the anterior margin of the shield, becoming thinner distally (Fig. 10I–J). Three rectangular elements preserved distally.
Raptorial appendages
Presence of three pairs of raptorial appendages recognised by preservation of muscles, protruding from the ventral margin, posterior to the presumed cephalic appendages. Raptorial appendages consisting of two parts: a proximal postero-ventrally oriented and a distal one, antero-ventrally oriented. Articulation between both parts forming an elbow.
First pair of raptorial appendages protruding from the ventral notch (Fig. 10E–F). Proximal part formed by two rectangular podomeres (podomeres 1 and 2). Distal part consists of at least one podomeres (podomere 3).
Second pair of raptorial appendages consisting of a proximal part with at least two rectangular podomeres (Fig. 10E–F). Distal part of the second raptorial appendages ending distally in a cluster of three spines.
Third pair of raptorial appendages ending distally in a cluster of five spines (Fig. 10E–F).
Posterior trunk
Long, tubular-like structure consisting of longitudinal muscles, extending from the anterior part of the shield to the posterior notch, interpreted as part of the posterior trunk (Fig. 10A–D). Nine trunk segments preserved under the shield, consisting of a rectangular pleural part, slightly curved downward at its distal end (Fig. 10H). Pleural parts decreasing in length toward the last segment. Presence of a circular structure at the posterior extremity of the trunk (Fig. 10A–D).
Posterior trunk appendages
Remnants of nine pairs of trunk appendages protruding from the posterior part of the ventral margin; appendages postero-dorsally oriented and poorly preserved, preventing their morphology from being determined (Fig. 10A–D).
Gills
Eight lamellar gills preserved under the central part of the shield, below the lateral carina (Fig. 10A–D). Gills becoming more arcuate toward the posterior part of the shield.
Anterior muscles
Presence of a bundle of radially arranged muscles close to the antero-ventral corner of the shield (Fig. 10A–D).
Remarks
The morphology of Mayrocaris sp. from La Voulte-sur-Rhône Lagerstätte is similar to that of Mayrocaris bucculata from Solnhofen-type Lagerstätten (Laville et al. 2021a): presence of a carina and of serrations on the dorsal midline, postero-dorsal corner expressed as a rounded spine, posterior and ventral notches, morphology and orientation of trunk segments, raptorial and trunk appendages, and of gills. The main difference is the ornamentation: no scale-like structures are visible on the shield of the La Voulte specimens. However, this might be due to poor preservation. Until better-preserved specimens are discovered, these specimens cannot be unambiguously assigned to a particular species.
description: Published as part of Laville, Thomas, Forel, Marie-Béatrice & Charbonnier, Sylvain, 2023, Re-appraisal of thylacocephalans (Euarthropoda, Thylacocephala) from the Jurassic La Voulte-sur-Rhône Lagerstätte, pp. 1-61 in European Journal of Taxonomy 898 (1) on pages 22-25, DOI: 10.5852/ejt.2023.898.2295, http://zenodo.org/record/8413500