Paraclausocaris harpa, 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 : 30-35

Paraclausocaris harpa gen. et sp. nov.

urn:lsid:zoobank.org:act:4F007D44-251E-496D-818B-9C3065947B0D

Figs 5A , 13–15

Clausia sp. – Secrétan & Riou 1983: 85–86, pl. 4 figs 2, 17.

Clausia ribeti – Secrétan 1985: 388, fig. 5j.

Clausocaris ribeti – Polz 1989: 73. — Charbonnier 2009: 158, fig. 250. — Charbonnier et al. 2010: 118, fig. 5d; 2014: 375, fig. 5c.

Dollocaris ingens – Charbonnier et al. 2010: 113, fig. 3e.

Diagnosis

Same as for Paraclausocaris .

Etymology

Referring to the shape of the shield, which is similar to the shape of a harp.

Material examined

Holotype FRANCE • La Boissine, La Voulte-sur-Rhône, Ardèche; Callovian, Middle Jurassic; MNHN.F.A 29295 .

Paratypes FRANCE • 22 specs; same collection data as for holotype; MNHN.F. A29148 , A29149 , A29264 , A29267 A29295 , A29323 , A29327 , A29345 , A29348 , A29353 , A29356 , A29358 , A29360 , A53341 , A83986 to A83990 , A84072 , R50955 , R50974 .

Measurements

See Table 2 .

Description

Shield morphology

Cone-shaped shield in lateral view with an anterior margin formed by a symmetric and concave optic notch in its ventral part and with a convex dorsal part, a sharp antero-dorsal corner, a slightly convex dorsal midline with small serrations in the last two thirds of the midline and ending in a sharp postero-dorsal corner ( Figs 13A, C, H , 14G–H ); straight posterior margin antero-ventrally oriented, ending in a rounded postero-ventral corner; ventral margin divided in a concave posterior part steeply descending antero-ventrally and in a horizontal anterior part slightly rising to the antero-ventral corner. Rims of all free margins forming a marginal fold.

Shield macro-ornamentation

Small sinuous ridges covering the entire dorsal area of the shield ( Fig. 13F ). Central part of the shield adorned with a straight dorso-lateral carina ( Fig. 14A–B ). Shield forming a hump near the antero-ventral corner ( Fig. 14A–B ). Thin ventro-lateral groove delimiting the marginal fold. Four rounded, canal-like pores visible in the posterior part of the shield, above the pleural part of trunk segments ( Fig. 13F–G ). Pores forming a rim surrounding a hollow part.

Sensory structures

Two stalked, circular compound eyes protruding from the optic notch and occupying most of the anterior margin ( Fig. 14A–B ). Eyes consisting of 136 hexagonal ommatidia per mm² (w = ~73 µm; h = ~130 µm; Figs 13E , 14E , 15H ).

Cephalic appendages

One elongate, antenniform structure (~ 15 mm) lying in the anterior part of the body ( Figs 13A, C , 14C–D ).

Raptorial appendages

Three pairs of long and slender raptorial appendages recognised by the 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 ( Figs 13H–I , 15F–G ), the shortest, consisting of a proximal part with two podomeres: podomere 1 being 3.4 times as long as wide; podomere 2 being 4.6 times as long as wide and longer than podomere 1. Distal part of the appendages formed by three podomeres: podomeres 3 being 4.3 times as long as wide; podomere 4 being 3.3 times as long as wide; podomere 5, the most distal one, being 3 times as long as wide, ending in a cluster of three long spines.

Second pair of raptorial appendages consisting of a proximal part with two podomeres: podomere 1 being 3.4 times as long as wide, podomere 2 being 6.2 times as long as wide ( Figs 14A–B , 15F, I ). Distal part of the appendage consisting of three podomeres: podomere 3 being 4.7 times as long as wide; podomere 4 being 5.5 times as long as wide; podomere 5, being 3.2 times as long as wide and ending distally in a cluster of three long spines.

Third pair of raptorial appendages, the longest, consists of a proximal part formed by two podomeres: podomere 1 being 3.6 times as long as wide; podomere 2, the longest of the appendages, being 6 times as long as wide ( Fig. 15A, F–G ). Distal part consisting of three podomeres: podomere 3 being 4.4 times as long as wide; podomere 4 being 5.7 times as long as wide and bearing three long spines on its medial end; podomere 5 being 3.3 times as long as wide and ending with a cluster of three long spines.

Oval structure

Long oval structure, protruding from the anterior part of the ventral margin, posterior to raptorial appendages ( Figs 13H–I , 15A, C, G–H ).

Posterior trunk

Posterior trunk consists of nine rectangular segments, slightly tilted anteriorly. Segments consisting of a dorsal square-shaped structure (i.e., tergal part of the segments), surrounded on their lateral sides by nine elongate rectangular structures (i.e., pleural part; Fig. 15G–H, J ), slightly curved downward at their distal end ( Fig. 15A, D ). Segments increasing in height towards the penultimate segment. Most posterior segment shorter than the previous one.

Posterior trunk ending posteriorly in a rhomboidal element (i.e., telson), bearing a circular structure formed by two circular parts ( Fig. 14A–D ): an outer one, delimiting the entire feature, and an inner smaller one.

Posterior trunk appendages

Nine pairs of posterior trunk appendages protruding from the posterior part of the ventral margin ( Fig. 13A–D ). First appendage formed by two parts: a square-shaped dorsal one (i.e., endopod) and a ventral oval one (i.e., exopod). Trunk appendages 2–8 consist of at least two elements: a square-shaped proximal one and a rectangular distal one. Last pairs of trunk appendages being much longer than the rest ( Fig. 14F–G ). No square-shaped element discernible.

Gills

Eight lamellar gills preserved under the central part of the shield below the lateral carina ( Fig. 14A–B ). Gills arcuate with an elliptic shape.

Anterior muscles

Bundle of radially arranged muscles preserved in the antero-medial part of the shield, above the antero-ventral hump ( Fig. 13A, C ).

Remarks

Some specimens previously assigned to Clausocaris ribeti (now Ostenocaris ribeti comb. nov.) are now ascribed to Paraclausocaris harpa gen. et sp. nov. (e.g., MNHN.F.A29149; Fig. 13H–I ; Charbonnier et al. 2010). Indeed, they differ from the type material (and thus from Ostenocaris ) by their well-developed optic notch, their serrated dorsal margin, their concave posterior part of the ventral margin and their elongate raptorial appendages relative to the shield size.

Figures

Fig. 5. Scatter plots of length of the shield against maximal height of the shield. A. Kilianicaris lerichei Van Straelen, 1923. B. Ostenocaris ribeti (Secrétan, 1985) comb. nov. C. Paraclausocaris harpa gen. et sp. nov. D. Paraostenia voultensis Secrétan, 1985. Abbreviations: Hmax = maximal shield height; Ls = length of the shield.

Fig. 13. Paraclausocaris harpa gen. et sp. nov. A–G. Holotype MNHN.F.A29295. A. General view of the part. B. General view of the counter-part. C. Drawing of the part. D. Close-up of the posterior trunk. E. Close-up of cephalic appendages. F. Close-up of the ornamentation. G. Close-up of pores. H–I. Paratype MNHN.F.A29148.H. General view.I. Drawing.Abbreviations: ca = cephalic appendages; ce = compound eye; dm = dorsal midline; en = putative endopod of posterior trunk appendage; ex = putative exopod of posterior trunk appendages; g = gills; mu = muscles; on = optic notch; os = oval structure; p1–5 = podomeres of raptorial appendages; po = pore; ra 1–3 = raptorial appendages; st = stalk; t = trunk; ta 2–8 = posterior trunk appendages; tls = telson; tp 1–9 = pleural part of posterior trunk segments; ts1–7 = trunk segments; vm = ventral margin. Scale bars: A–D, F = 5 mm; E = 2 mm; G = 1 mm; H–I = 10 mm. Photos: A–B: Lilian Cazes; D–H: T. Laville.

Fig. 14. Paraclausocaris harpa gen. et sp. nov. A–E. Paratype MNHN.F.A29327. A. General view. B. Drawing. C. Close-up of cephalic appendage. D. Close-up of cephalic appendage (colour-marked). E. Close-up of compound eyes. F–G. Paratype MNHN.F.A29149. F. General view. G. Close-up of posterior part. Abbreviations: ca = cephalic appendage; ce = compound eye; dm = dorsal midline; dlc = dorso-lateral carina; g = gills; hu = hump; ls = left side of the shield: mu = muscles; on = optic notch; os = oval structure; p2–5 = podomeres of raptorial appendages; ra1–3 = raptorial appendages; rs = right side of the shield; vlg = ventro-lateral groove. Scale bars: A–B, G = 5 mm; C–D = 2 mm; E = 500 µm; F = 10 mm. Photos: T. Laville.

Fig. 15. Paraclausocaris harpa gen. et sp. nov. A, C–D. Paratype MNHN.F.A29356. A. General view. C. Close-up of oval structure. D. Close-up of posterior trunk. B, E. Paratype MNHN.F.A29323. B. General view. E. Close-up of compound eye. F–G, J. Paratype MNHN.F.R50955. F. General view. G. Drawing. J. Close-up of posterior trunk. H–I. Paratype MNHN.F.A29323. H. General view. I. Closeup of distal part of raptorial appendages. Abbreviations: ce = compound eye; on = optic notch; os = oval structure; ltp = left pleural part of posterior trunk; p 1–4 = podomeres of raptorial appendages; ra 1–3 = raptorial appendages; rtp = right pleural part of posterior trunk; ta 2–8 = trunk appendages; tp 2–8 = pleural part of posterior trunk; tt1-9 = tergal part of posterior trunk; vm = ventral margin; vlg = ventro-lateral groove. Scale bars: A–B, H, J = 5 mm; C–D, I = 1 mm; E = 200 µm; F–G = 10 mm. Photos: T. Laville.