Lepidothelphusa Colosi, 1920

Grinang, Jongkar & Ng, Peter K. L., 2015, Taxonomy of the semiterrestrial crab Lepidothelphusa cognettii (Nobili, 1903) (Crustacea: Decapoda: Brachyura: Gecarcinucidae), with descriptions of five new species from Sarawak, Malaysia, Borneo, Raffles Bulletin of Zoology 63, pp. 564-582 : 565

Lepidothelphusa Colosi, 1920

Parathelpusa ( Lepidothelphusa ) Colosi, 1920: 24. Para-Lepidothelphusa cognetii – Balss, 1937: 174. Lepidothelphusa – Bott, 1970: 55.

Type species. Potamon (Geotelphusa) cognettii Nobili, 1903 ; by original designation; gender of genus feminine.

Diagnosis. Carapace quadrate, slightly wider than long, dorsal surface relatively flat, smooth to rugose; cervical and H-grooves visible, shallow to deep; anterolateral margins not clearly demarcated from posterolateral margins, lateral margins subparallel; epibranchial tooth undiscernible; frontal median triangle absent; epigastric and postorbital cristae distinct, margins gently serrated; lateral margins of posterior epistome gently concave, entire; ischium of third maxilliped rhomboidal without discernible sulcus, exopod flagellum very short; adult male major cheliped prominently enlarged, chela swollen, large, fingers slightly to strongly gaping, cutting edges with prominent teeth; inner margin of merus of cheliped with expanded projection with serrated margin; ambulatory legs relatively long, slender; anterior male thoracic sternum (sternites 1–4) longitudinally compressed, sterno-abdominal cavity reaching to base of buccal cavity; male abdomen triangular, somite 6 trapezoidal, telson elongate; G1 relatively stout; terminal segment subcylindrical, straight to curving outwards, gradually tapering to rounded tip, about half of length of subterminal segment; G2 with long distal segment about half of length of basal segment.

Remarks. In examining specimens of Potamon (Geotelphusa) cognettii Nobili, 1903 , Colosi (1920) suggested that the species must be removed from the genus Potamon and referred to Parathelphusa . He established a new subgenus, Lepidothelphusa , for the species and gave a brief description, indicating for the first time that it had bilobed mandibular palps. This character clearly shows that the species belongs to the family Gecarcinucidae (see Ng, 1988; Ng et al., 2008). Lepidothelphusa can be distinguished from almost all other freshwater gecarcinucids from Southeast Asia by its squarish carapace (with the width just longer than the length and the lateral margins subparallel) with the dorsal surfaces smooth or slightly rugose; there is no epibranchial tooth; there is no frontal median triangle; the lateral margins of the posterior margin of the epistome are almost entire; the ischium of the third maxillipeds does not have a visible sulcus and the flagellum on the exopod is poorly developed; the distinctive asymmetrical adult male chelipeds with gaping fingers (very strong in some species); the presence of a welldeveloped serrated projection on the merus of the chelipeds; the male sterno-abdominal cavity reaching all the way to the buccal cavity; the G1 is relatively stout; and the G2 is shorter than the G1 (see also Nobili, 1903; Bott, 1970; Ng, 2004). Lepidothelphusa cognettii s. str. and five new species described herein all have the typical generic characters.

There is some variation in some of the diagnostic characters is quite consistent among the species. The serrated projection on the inner margin of the merus of the chelipeds is relatively more prominent in larger males and is less well-developed in juveniles and female specimens. The chelipeds are also more prominently asymmetrical in larger male specimens.