Pseudastacus lemovices, Charbonnier & Audo, 2020

Charbonnier, Sylvain & Audo, Denis, 2020, A new stenochirid lobster (Crustacea, Decapoda, Stenochiridae) from the Early Jurassic of France, Geodiversitas 42 (7), pp. 93-102 : 97-99

Pseudastacus lemovices n. sp.

( Figs 2-6 )

urn:lsid:zoobank.org:act:D58E5862-AD82-4B39-96D4-56BED134F76D

ETYMOLOGY. — The specific epithet refers to the “Lemovices” (used as a noun in apposition), a Gaulish tribe of Central Europe who established themselves in Limousin and Poitou regions between 700 and 400 BC. The type locality Chauffour-sur-Vell is located in Limousin.

TYPE MATERIAL. — Holotype: CN-NMP-130-1.

Paratypes: 4, CN-NMP-130-2 to CN-NMP-130-5. All are preserved in compression at the surface of a single slab of limestone.

TYPE LOCALITY. — Chauffour-sur-Vell, Corrèze department, Limousin, Nouvelle-Aquitaine region, France.

TYPE AGE. — Early Jurassic, Sinemurian (after Lefavrais-Raymond et al. 1976).

DESCRIPTION

Carapace

Subcylindrical carapace (length, excluding rostrum: c. 11 mm; height: c. 6.5 mm); straight dorsal margin; ventral margin poorly preserved; triangular rostrum, elongate, relatively large, with pointed distal extremity, bearing three lateral spines; deep cervical groove, subvertical at level of dorsal margin and ventrally curved before joining concave antennal groove; sinuous branchiocardiac groove joined ventrally to rounded hepatic groove; large and deep orbital incision, ventrally limited by antennal spine.

Pleon

Somite 1, smallest than the others; somites 1 to 5 (s1-s5) with rounded pleura, almost straight anteriorly and concave posteriorly; s2-s5 with longitudinal carina separating tergopleuron from the rest of the tergum; s6 shorter than s5; telson poorly preserved. Cephalic appendages

Rounded eye (preserved only on paratype CN-NMP-130-4); antennulae (a1) poorly preserved, short, with multi-articulated flagella; antennae (a2) composed of elongate antennal peduncle bearing large, elongate, and pointed scaphocerite, and strong multi-articulated flagella; third maxilliped, elongate and smooth;

Thoracic appendages

Pereiopods 1 to 5 (P1-P5) decreasing in size posteriorly; chelate pereiopods 1 to 3 (P1-P3); P1 larger and longer than P2 and P3; short and stout P1 chela with index and dactylus of equal length, with slightly curved distal extremity and finely serrated occlusal margins; dorsal margin of P1 merus with one longitudinal median row of strong tubercles; P1 carpus and propodus with smooth dorsal margin; small P2 and P3 chelae with index and dactylus of equal length, slightly curved distal extremity; P4 and P5, smallest and smooth, poorly preserved.

Pleonal appendages

Pleopods not preserved; uropods of equal length, with distal margins fringed by elongate setae; uropodal exopod with longitudinal median carina and straight diaeresis.

Ornamentation

Carapace uniformly covered by small pits; pereiopods smooth; pleonal somites smooth. Some specimens show a relatively smooth carapace. Thus, the carapace ornamentation is variable in aspect, according to which of the cuticle layers are preserved: smooth or finely pitted; both aspects may in fact correspond to diverse degrees of abrasion and/or decortication of carapace (similar cases were observed in erymid lobsters: see Charbonnier et al. 2014; Hyžný et al. 2015).

DISCUSSION

The new species possesses anatomical characters typical of Astacidea : the first three pereiopods are chelate, the first pereiopods are stronger than the others, there are no midlateral hinges between the pleonal somites, the cervical groove is deep and the branchiocardiac groove is oblique. Moreover, following the key proposed by Wahle et al. (2012), the new species is assigned to the family Stenochiridae based upon the following characters: rostrum bearing lateral spines; cervical groove extends transversely from dorsomedian; branchiocardiac groove extends obliquely across lateral portion of carapace; uropodal exopod with diaeresis; pereiopods 2 and 3 bearing very small chelae. More precisely, the new species is assigned to Pseudastacus Oppel, 1861b based on the typical groove pattern of the carapace (deep cervical groove crossing dorsal midline; welldeveloped branchiocardiac groove, joined ventrally to hepatic groove), the elongate triangular rostrum with three lateral spines; the short and stout P1 chela. Pseudastacus lemovices n. sp. differs from P. pustulosus by the ornamentation of the carapace (uniformly covered by tubercles in P. pustulosus; uniformly covered by pits in P. lemovices n. sp.) and of the first pereiopod (uniformly covered by tubercles in P. pustulosus; smooth in P. lemovices n. sp.).

In addition, this association of five specimens may suggest a mass mortality event linked to an environmental stress (e.g., anoxia, temperature). It may also point to a gregarious behaviour as observed in different extant and fossil lobsters (see Klompmaker & Fraaije 2012 and references therein).

Figures

FIG. 2. — Holotype CN-NMP-130-1 of Pseudastacus lemovices n. sp. from the Sinemurian of Chauffour-sur-Vell, France: A, specimen in right lateral view, cross-polarized light; B, interpretative line drawing. Abbreviations: a, branchiocardiac groove; b, antennal groove; b1, hepatic groove; ca, carpus; di, diaeresis; en, uropodal endopod; ex, uropodal exopod; e1e, cervical groove; pr, propodus; P1-P4, pereiopods 1 to 4; me, merus; r, rostrum; sc, scaphocerite; se, setae; s1-s6, pleonal somites 1 to 6. Photograph: D. Audo. Scale bars: 5 mm.

FIG. 3. — Paratype CN-NMP-130-2 of Pseudastacus lemovices n. sp. from the Sinemurian of Chauffour-sur-Vell, France: A, specimen in right lateral/ventral view, cross-polarized light; B, interpretative line drawing. Abbreviations: a2, antenna; ca, carpus; pr, propodus; P1-P5, pereiopods 1 to 5; me, merus; mxp3, third maxilliped; s1-s6, pleonal somites 1 to 6. Photograph: D. Audo. Scale bars: 5 mm.

FIG. 4. — Paratype CN-NMP-130-3 of Pseudastacus lemovices n. sp. from the Sinemurian of Chauffour-sur-Vell, France: A, specimen in left lateral/dorsal view, cross-polarized light;B, interpretative line drawing.Abbreviations:di, diaeresis; en, uropodal endopod;ex, uropodal exopod; e1e, cervical groove; P1-P3, pereiopods 1 to 3; r, rostrum; se, setae; sk, endophragmal skeleton; s1-s4, pleonal somites 1 to 4. Photograph: D. Audo. Scale bars: 5 mm.

FIG. 5. — Paratype CN-NMP-130-4 of Pseudastacus lemovices n. sp. from the Sinemurian of Chauffour-sur-Vell, France: A, specimen in left lateral view, cross-polarized light; B, interpretative line drawing.Abbreviations:a, branchiocardiac groove;as, antennal spine; a1, antennula;a2, antenna; b, antennal groove; b1, hepatic groove; e1e, cervical groove; o, eye; r, rostrum; sc, scaphocerite; s1-s6, pleonal somites 1 to 6; t, telson. Photograph: D. Audo. Scale bars: 5 mm.

FIG. 6. — Paratype CN-NMP-130-5 of Pseudastacus lemovices n. sp. from the Sinemurian of Chauffour-sur-Vell, France: A, specimen in ventral view, cross-polarized light; B, interpretative line drawing. Abbreviations: e1e, cervical groove; md, dorsal midline; P2-P4, pereiopods 2 to 4; r, rostrum; sc, scaphocerite; s1-s2, pleonal somites 1 to 2. Photograph: D. Audo. Scale bars: 5 mm.