Cancer sp.

Charbonnier, Sylvain, Garassino, Alessandro, Pasini, Giovanni & Chény, Cédric, 2024, Review of brachyuran crabs from the late Miocene (Messinian) of Oran, Algeria, Geodiversitas 46 (2), pp. 13-29 : 22

Cancer sp.

( Fig. 4F )

Cancer sp. – Van Straelen 1937: 447.

EXAMINED MATERIAL. — MNHN.F.A51742 (Arambourg coll.) from the Messinian of Les Planteurs quarry , Sanaouber district of Sidi El Houari, Oran .

DESCRIPTION

Giant left P1 chela (length: ca 9 cm from index apex to carpopropodial articulation), dorsal margin strongly convex, bearing strong tubercules; ventral margin almost straight and smooth; index slightly curved with smooth occlusal margin; dactylus strongly curved with smooth occlusal margin; occlusal opening wide; palm without carinae but with outer surface uniformly covered by very small scaly pits; index and dactylus bearing brownish coloured pattern contrasting with whitish general colour of chela.

DISCUSSION

Van Straelen (1937) proposed to place this isolated P1 chela in Cancer sp. based on its similarity with the robust chelae of Cancer pagurus . He added that the curvature of the dactylus was different from this extant species. Our examination leads to highlight some new characters: occlusal margin of index strongly incurved and smooth, smooth occlusal margin of dactylus, and strongly convex dorsal margin of propodus with at least three big tubercles. These characters do not fit those of C. pagurus , which shows the P1 chela with occlusal margins of fingers bearing molariform teeth and straight smooth dorsal margin of propodus. Based on Nations (1975), some species of Cancer show the dorsal margin of propodus with spines or tubercles, but the margin is always straight or slightly convex and the occlusal margins of both finger always bearing big teeth. Moreover, all species of Cancer show the outer surface of palm with a variable number of raised tuberculate carinae. The subquared outline of the P1 palm from Oran is also reminiscent of the P1 palm of some extant genera ( Anatolikos Schweitzer& Feldman, 2000 , Glebocarcinus Nations, 1975 , and Platepistoma Rathbun, 1906 ). However, all the P1 chela of these living genera bear occlusal margin with molariform teeth and longitudinal carinae on palm (see Schram & Ng 2012: fig. 2). In conclusion, according to Van Straelen (1937), we leave this giant P1 chela in open nomenclature within Cancer , though it could represent a new species of cancrinid crab. We point out the orange brown colour pattern of the fingers, which constitutes a case of exceptional preservation

Figures

FIG. 4. — Cancrid crabs from the late Messinian of Oran (Les Planteurs quarry, Arambourg coll.): A-E, Cancer sismondai Meyer, 1843: MNHN.F.A51761, dorsal and ventral views (A, B); MNHN.F.A51741, dorsal and ventral views (C, D); MNHN.F.A51740, ventral view (E); F, Cancer sp., MNHN.F.A51742, outer view of P1 chela. Scale bars: 2 cm. Photographs: Lilian Cazes.