Dardanus sp.

Pasini, Giovanni, Garassino, Alessandro & Sami, Marco, 2018, Decapod crustaceans from the late Pliocene (Piacenzian) nearby Faenza (Emilia-Romagna, N Italy), Natural History Sciences 5 (2), pp. 27-32 : 28

Dardanus sp.

( Fig. 1A, B )

Material and measurements: one complete right chela palm from Pietramora-Ca’ Castello ( MSF 2251 – lp: 21 mm; wp: 16 mm; ld: 15 mm; li: 16 mm).

Description. Subrectangular palm, longer than wide; upper margin convex, lower margin nearly straight; outer surface covered with granulated transverse and sinuous ridges; inner surface slightly convex with the same ornamentation of the outer surface on the median upper part, nearly smooth along the lower inner surface; subtriangular, robust dactylus and index with transverse ridges; index slightly longer than dactylus.

Discussion. The studied specimen shows an outer surface of the palm ornated by transverse and sinuous ridges that are a typical distinctive character of some representatives of Dardanus Paul’son, 1875, which the specimen is assigned to.

The studied specimen was compared with the two Plio-Pleistocene Mediterranean species of the genus, Dardanus substriatus (A. Milne Edwards, 1861) (fossil) and D. arrosor (Herbst, 1796) (extant and fossil), sharing some morphological affinities. The studied specimen, however, differs from the right palm D. arrosor in having less elongate palm, less coarse and more transverse ridges on the outer surface of the palm and more elongate index (for comparison see Garassino et al. 2014: 121; fig. 1B). Moreover, the studied specimen differs from the left palm of D. substriatus (the right palm is unknown), in having more subrectangular elongated palm with lower and upper margins not strongly converging anteriorly and less coarse granulated transverse, sinuous ridges (for comparison see Garassino et al., 2014: 121; fig. 1C). We point out that the characters observed on the studied specimen could be also included into the variability of this species having most probably unequal chelae as all representatives of the family. Based on the limited comparisons only the discovery of additional specimens would allow us to solve the systematic position of the studied specimen.

Figures

Fig. 1 - Dardanus sp., MSF 2251. A) right palm, outer view. B) right palm, inner view (x 2).