Nakhonsimon, Promdam & Nabhitabhata & Ng, 2014

Promdam, Rueangrit, Nabhitabhata, Jaruwat & Ng, Peter K. L., 2014, Nakhonsimon ramromensis, a new genus and species of freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from Nakhon Si Thammarat, Peninsular Thailand, Raffles Bulletin of Zoology 62, pp. 496-500 : 496-497

Nakhonsimon , new genus

Type species. Nakhonsimon ramromensis , new species, designated herein.

Diagnosis. Dorsal carapace regions well demarcated; anterolateral margins convex; epibranchial tooth low. Surfaces of carapace, chelipeds, and ambulatory legs with numerous short stiff setae. Posterior margin of epistome with sharp median triangle, lateral margins sinuous. Exopod of third maxilliped extending beyond distal margin of ischium, reaching lower than half level of merus length, without flagellum. Ambulatory legs relatively long, articles slender. Male thoracic sternites 3, 4 separated by a distinct groove. G1 distinctly curved; curvature mainly in slender, subterminal segment; terminal segment straight, longer than half length of subterminal segment, spatuliform. G2 distal segment longer than half length of basal segment.

Etymology. The name is an arbitrary combination of Changwat (= Province) Nakhon Si Thammarat, the type locality of the type species, in combination with the genus name Potamon . Gender of genus neuter.

1 Department of Biology, Faculty of Science, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand

2 Excellence Centre for Biodiversity of Peninsular Thailand (CBIPT), Faculty of Science, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand; Email: [e-mail], [e-mail] (* corresponding author)

3 Lee Kong Chian Natural History Museum, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore; Email: [e-mail]

© National University of Singapore

ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)

Remarks. Nakhonsimon , new genus, appears to be morphologically closest to Stoliczia Bott, 1966 (type species Telphusa stoliczkana Wood-Mason, 1871 ) in the general shape and structure of the carapace, and in having no flagellum on the exopod of the third maxilliped. Stoliczia contains 15 species and is distributed across the northern half of Peninsular Malaysia to southern Thailand ( Ng 1988, 1992b, 1993, 2004; Ng et al., 2008), Nakhonsimon , however, differs in several important respects, viz. male thoracic sternites 3 and 4 are separated by a distinct groove ( Fig. 1C ) (versus not visible in Stoliczia , with thoracic sternites 3 and 4 completely fused to each other); the relatively longer ambulatory merus (ratio of length of last ambulatory merus to median length of carapace, 0.60, versus 0.43 ‒ 0.59 in Stoliczia species ) ( Fig. 1A ); and the strongly curved G1 subterminal segment which has the distal portion slender ( Fig. 2B, C ) (versus straighter subterminal segment of G1 with the distal portion relatively broader, gradually tapering distally in Stoliczia ) (cf. Ng, 1988: figs. 24–36; Ng, 1992b: figs. 4A–E, pl. 3 fig. A; Ng, 1993: figs. 3A, C–F, 4A–E, 5A, C–F, pl. 3 fig. A, pl. 4 fig. A; 2004: fig. 8J).

Johora Bott, 1966 , which occurs from southern Thailand to Singapore, is also morphologically similar to Nakhonsimon in general shape and structure of the carapace. The G1s of Johora species , however, are never as strongly curved (cf. Ng 1987, 1988, 1990). Johara also differs from Nakhonsimon in possessing a distinct flagellum on the exopod of the third maxilliped, and having no visible groove between the male thoracic sternites 3 and 4 (cf. Ng, 1988: figs. 13–23; 2004: figs. 7G–K; Yeo, 2001: figs. 1A–C, F, 2C–F; Leelawathanagoon et al., 2005: figs. 1, 2A, B, D–F).

39A, 51A, 52A, 54A; Naiyanetr, 2001: fig. 1D; Brandis, 2002: fig. 16; Yeo & Ng, 2007: 280).

Figures

Fig.1. Nakhonsimon ramromensis, new genus and species, holotype, male, 31.8 × 24.6 mm, PSUNHM 211514-333-0005. A, dorsal view; B, frontal view; C, ventral view.

Fig. 2. Nakhonsimon ramromensis, new genus and species, holotype, male, 31.8 × 24.6 mm, PSUNHM 211514-333-0005. A, left third maxilliped; B, ventral view of left G1; C, dorsal view of left G1; D, left G2. Scale bars = 2.0 mm.