Austriocaris secretanae, Laville & Forel & Charbonnier, 2023

Laville, Thomas, Forel, Marie-Béatrice & Charbonnier, Sylvain, 2023, Re-appraisal of thylacocephalans (Euarthropoda, Thylacocephala) from the Jurassic La Voulte-sur-Rhône Lagerstätte, European Journal of Taxonomy 898 (1), pp. 1-61 : 11-15

Austriocaris secretanae sp. nov.

urn:lsid:zoobank.org:act:1AE5E1E4-F48D-4D36-BD5B-3CDC7225DE95

Figs 3–4

Dollocaris ingens – Secrétan 1985: 381–386, fig. 5a–b. — Charbonnier et al. 2010: 119, fig. 6d; 2014: 375, fig. 4a.

Diagnosis

Austriocaris with stout and long raptorial appendages, the third pair having spines on the second and third podomeres of the distal part, and a posterior trunk consisting of 12 segments bearing rod-like appendages. Absence of ventro-lateral structure.

Etymology

In reference to Sylvie Secrétan (CNRS, Paris), for her important contribution to the study of La Voulte-sur-Rhône thylacocephalans.

Material examined

Holotype FRANCE • La Boissine, La Voulte-sur-Rhône, Ardèche ; Callovian, Middle Jurassic; MNHN.F. R50963 .

Paratypes FRANCE • 6 specs; same collection data as for holotype; MNHN.F. A29249 , A29257 , A29286 , A84029 , R06203 , R50971 • 3 specs; same collection data as for holotype; MSNM i7591 , i13276 , i13603 .

Measurements

See Table 2 .

Description

Shield morphology

Sub-oval shield in lateral view with a short, sinuous anterior margin, a sharp antero-dorsal corner, a straight and horizontal dorsal midline, endings posteriorly in a sharp postero-dorsal corner, a posterior margin divided into a very short and straight dorsal part antero-ventrally oriented and a straight, sub-vertical ventral part, a rounded postero-ventral corner, a ventral margin divided into a posterior half, steeply descending antero-ventrally and a horizontal anterior part merging approximately at the posterior third of the length, a rounded antero-ventral corner ( Fig. 3A–D ). Rim of all free margins delimiting a marginal fold.

Shield macro-ornamentation

Shield with a dorso-lateral carina located on its anterior area and a medio-lateral carina protruding from the postero-ventral angle ( Fig. 3 ). Dorso-lateral carina horizontal until mid-length of the shield where it folds down on itself. Presence of a row of 33 pores on the top of the carina ( Fig. 3E ). Medio-lateral carina horizontal until mid-length then becoming antero-ventrally oriented. Rim of all free margins delimiting the marginal fold. Shield also ornamented with horseshoe-like ridges ( Fig. 4A, C ).

Sensory structures

Large, oval, stalked compound eyes protruding from the anterior margin and occupying the entire margin ( Fig. 3H–I ). Eyes tilted in the same orientation as the anterior margin, formed by hexagonal ommatidia

(w = ~65 µm; l = ~70 µm, about 196 per mm²; Fig. 4A, F ).

Cephalic appendages

Cephalic appendages not preserved.

Raptorial appendages

Presence of three pairs of stout raptorial appendages recognised by preservation of muscles, protruding from the anterior part of the ventral margin ( Fig. 3A, C ). Raptorial appendages consisting in 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 ( Fig. 3H–I ), the shortest, consisting of a proximal part with two rectangular podomeres: podomere 1 being 4.2 times as long as wide; podomere 2 being 4.7 times as long as wide. Distal part of the appendages formed by three rectangular podomeres: podomere 3 being 3.4 times as long as wide, bearing six spines on its medial margin; podomere 4 being 2.3 times as long as wide; podomere 5, the shortest, being 1.4 times as long as wide and ending in a cluster of three spines.

Second pair of raptorial appendages consisting of a proximal part with two podomeres ( Fig. 3A, C ): podomere 1 being 4.7 times as long as wide; podomere 2, the longest, being 5.3 times as long as wide. Distal part of the appendage consisting of three podomeres: podomere 3 being 3.2 times as long as wide; podomere 4 being 3.1 times as long as wide; podomere 5 being 1.5 times as long as wide and ending distally in a cluster of five spines.

Third pair of raptorial appendages, the longest, consisting of a proximal part formed by two rectangular podomeres ( Figs 3A–C , 4I–J ): podomere 1 being 3.2 times as long as wide; podomere 2, the longest, being 7.9 times as long as wide. Distal part consisting of three podomeres: podomere 3 being 5.2 times as long as wide; podomere 4 being 4.5 times as long as wide and bearing eight spines on its medial margin, the first two being close to the proximal margin ( Fig. 4I–J ), followed by two stout spines, surrounding a more gracile one, and then by three short spines and a long, stout spine. Distal part of the third raptorial appendages ending with a square-shaped podomere (podomere 5), bearing a cluster of three spines.

Oval structure

Long, oval structure protruding from the anterior part of the ventral margin, between raptorial and trunk appendages ( Fig. 3A–D, H–I ). Two elongate and sinuous rectangular structures visible on this feature. The nature of this structure is unknown.

Posterior trunk

Posterior trunk consisting of eleven elongate, rectangular structures (i.e., pleural parts of the segments; Figs 3A–D , 4D, G ), slightly curved upward at their distal end and surrounding a long rectangular structure (i.e., tergal part of posterior trunk segments). Last pleural part thinner than the other ones. Presence of a square-shaped element (i.e., telson) at the posterior extremity of the trunk, bearing a circular structure formed by two circular parts: an outer one, delimiting the entire feature, and an inner smaller one.

Posterior trunk appendages

Eleven pairs of rod-like trunk appendages posteriorly oriented and protruding from the posterior part of the ventral margin ( Figs 3A–D , 4E, H ).

Gills

Four long lamellar gills preserved under the posterior area of the shield below the medio-lateral carina ( Fig. 3H–I ).

Remarks

The specimens described above display typical characters of Austriocaris such as the well-developed optic notch restricted to the ventral part of the anterior margin, the large triangular rostrum, a straight dorsal mid-line ending in a spinous postero-dorsal corner. They differ from the type species, Austriocaris carinata , by the hook-shaped and tuberculate dorso-lateral carina, by the presence of horseshoe-like ridges and by the absence of a Y-shaped ventro-lateral carina. Thus, we consider these specimens as belonging to a new species: Austriocaris secretanae sp. nov.

Figures

Fig. 3. Austriocaris secretanae sp. nov. A–F. Holotype MNHN.F.R50963. A. General view (part). B. General view (counter-part). C. Drawing (part). D. Drawing (counter-part). E. Close-up of pores. F. Close-up of muscles of raptorial appendages. G. Paratype MNHN.F.A29257. H–I. Paratype MNHN.F.R06203. H. General view. I. Drawing. Abbreviations: am = anterior margin; ce = compound eye; dlc = dorso-lateral carina; dm = dorsal midline; g = gills; mlc = medio-lateral carina; os = oval structure; p1–5 = podomeres of raptorial appendages; pm = posterior margin; po = pores; ra 1–3 = raptorial appendages; sp = spines; st = stalk; t = posterior trunk; ta 8 = posterior trunk appendage 8; tp 1–11 = pleural parts of posterior trunk; vlg = ventro-lateral groove; vm = ventral margin. Scale bars: A–D, G–I = 10 mm; E = 1 mm; F = 5 mm. Photos: A–B, G: L. Cazes; E–F: T. Laville. H: C. Haug & Joachim T. Haug.

Fig. 4. Austriocaris secretanae sp. nov. A, C, F. Paratype MNHN.F.A29286. A. General view. C. Closeup of ornamentation. F. Close-up of compound eye. B. Paratype MNHN.F.R50971. D, G. Paratype MNHN.F.A29249. D. General view. G. Drawing. E–H. Paratype MNHN.F.A84029. E. General view. H. Close-up of posterior trunk appendages. I–J. Paratype MSNM i7591. I. General view. J. Close-up of raptorial appendages. Abbreviations: cs = circular structure; dm = dorsal midline; os = oval structure; pm = posterior margin; t = posterior trunk; tp1–11 = pleural parts of posterior trunk appendages. Scale bars: A–B, D–E, G, I = 10 mm; C = 1 mm; F = 400 µm; H, J = 5 mm. Photos: A, C–F, H–J: T. Laville; B: L. Cazes.