Gastroptychus Caullery, 1896

(Figs. 1B, 3A)

Ptychogaster A. Milne Edwards, 1880: 63 .— Henderson, 1888: 170 (part).— Alcock, 1901: 280 (part). Gastroptychus Caullery, 1896: 390 (replacement name for Ptychogaster A. Milne Edwards, 1880, preoccupied by Ptychogaster

Pomel, 1847 (Reptilia: Chelonia, fossil)).— Miyake & Baba, 1968: 379 (part).— Poore, 2004: 221 (part).— Baba, 2005: 19

(part).— Macpherson & Baba, 2011: 49 (part). Chirostylus — Zariquiey Alvarez, 1968: 261 (part).— Van Dam, 1933: 12 (part).

Type species. Ptychogaster spinifer A. Milne Edwards, 1880 .

Diagnosis. Carapace with dorsal and lateral spines; dorsal surface lacking transverse striae; lateral orbital spine present or absent; posterior lateral margin weakly or barely excavated. Rostrum spiniform, basal part subtriangular. Anterior margin of sternal plastron (at sternite 3 immediately behind maxillipeds 3) feebly or strongly concave with 2 or more spines, preceded by excavated sternum; sternite 4 with strong lateral spine on each side. Sternal plastron concavely constricted between sternites 4–5 (often hourglass-shaped). Antennal peduncle slender, acicle present or absent. Mandible incisor margin serrated. Maxilliped 1 exopod with smooth, non-annulated flagellum. Pereopods 1–4 long and slender, with numerous spines usually arranged in longitudinal rows.

Species included. Chirostylus affinis Chace, 1942 (western Atlantic); Gastroptychus brachyterus Baba, 2005 (western Pacific); Gastroptychus brevipropodus Baba, 1991 (western Pacific); Ptychogaster laevis Henderson, 1885 (western Pacific); Gastroptychus novaezelandiae Baba, 1974 (western Pacific); Gastroptychus paucispina Baba, 1991 (western Pacific); Ptychogaster spinifer A. Milne Edwards, 1880 (western Atlantic); Chirostylus

Remarks. Nine species are now assigned to Gastroptychus sensu stricto . Baba (2005) mistakenly placed

Ptychogaster spinifer in the other group of species of Gastroptychus, transferred herein to Sternostylus .

Three species ( G. brachyterus, G. brevipropodus, G. novaezelandiae) are unusual in the genus in having the pereopods 2–4 propodi extremely short relative to the carpi. Molecular data are available for G. novaezelandiae (see Schnabel et al. 2011; Bracken-Grissom et al. 2013) but a comparison of genetic differentiation from other members of this genus is yet to be undertaken.