Tiwaripotamon Bott, 1970

Ng, Peter K. L. & Tri, Ngo Van, 2022, A new semiterrestrial crab from limestone hills in Vietnam (Crustacea: Brachyura Potamidae: Tiwaripotamon), Zootaxa 5213 (5), pp. 578-586 : 579

Tiwaripotamon Bott, 1970

Type species. Geothelphusa annamensis Balss, 1914 , by original designation.

Remarks. The most distinctive features that define Tiwaripotamon are the smooth and transversely subovate carapace, with the epigastric and postorbital ridges almost undiscernible, the low or absent epigastric tooth, the exopod of the third maxilliped has a flagellum that is shorter than the width of the merus, the broadly triangular male pleon, and the very long ambulatory legs.

Although the genetic data indicates Tiwaripotamon is monophyletic for the time being ( Shih & Do 2014; Do et al. 2016), the known species have quite different G1 structures. The most common type of G1 has the subterminal segment gently curved, with the terminal segment tapering and with a low dorsal lobe is present on the proximal part (in T. edostilus , T. pingguoense , T. pluviosum , T. xiurenense ; cf. Dai & Naiyanetr 1994: figs. 1.4, 1.6, 2.4, 2.5; Ng & Yeo 2001: fig. 5D–K; Do et al. 2016: fig. 2A–F). The G1 of the new species, T. bellum n. sp. corresponds to this group. The G1 of the type species, T. annamense , is similar except that the terminal segment is gently upturned without any visible dorsal flap (cf. Ng & Yeo 2001: fig. 2D–I), whereas that of T. hamyen is curved, subconical and also without any dorsal flap (cf. Do et al. 2017: fig. 7A–D). The G1 of the other three species are all very distinctive and differ from the above pattern: in T. vietnamicum , the terminal segment is filiform and straight (Đăng & Hồ 2002: fig. 2E); in T. vixuyenense , the subterminal segment is short and stout with the terminal segment conical, short and without a flap ( Shih & Do 2014: fig. 3A–D, E–H); and in T. xuanson , the subterminal segment is almost straight with the terminal segment conical, tapering and upturned without a flap ( Do et al. 2017: fig. 4A–D). Only in T. araneum is the G1 not known, because the species is based only on one juvenile male collected from northern Vietnam ( Ng & Yeo 2001).