A NEW SPECIES OF THAIPOTAMON NG & NAIYANETR, 1993 (BRACHYURA, POTAMIDAE) FROM THAILAND BY PHAIBUL NAIYANETR1,3) and DARREN C.J. YEO2,4) 1) Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand 2) Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore ABSTRACT A new species of terrestrial potamid freshwater crab, Thaipotamon holthuisi sp. nov., is described from Thailand. Although species in this genus have a very conservative external mor- phology, the new species can be differentiated from its closest congeners by the characteristic form of the male first pleopod. RÉSUMÉ Une nouvelle espèce de crabe d’eau douce Potamidae, Thaipotamon holthuisi sp. nov., est décrite de Thailande. Bien que les espèces de ce genre aient une morphologie externe très constante, la nouvelle espèce peut se différencier de ses plus proches congénères par la forme caractéristique du premier pléopode male. INTRODUCTION Potamid freshwater crabs of the genus Thaipotamon Ng & Naiyanetr, 1993, are characterised morphologically by a smooth, swollen carapace; third maxillipeds with a distinctly curved exopod bearing a short but well-developed flagellum; broadly triangular male abdomen; long, slender ambulatory dactyli: and the male first pleopods with a “hook-like” terminal segment bearing a very 3) e-mail: [email protected] 4) Corresponding author; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2010 Studies on Malacostraca: 529-534 530 CRM 014 – Fransen et al. (eds.), LIPKE BIJDELEY HOLTHUIS MEMORIAL VOLUME high and broad dorsal flap (Ng & Naiyanetr, 1993). Thaipotamon species are terrestrial crabs, being often found on the forest floor away from surface water (Yeo et al., 2008). The genus includes six species to date: T. chulabhorn Naiyanetr, 1993, T. dansai Ng & Naiyanetr, 1993, T. lomkao Ng & Naiyanetr, 1993 [type species], T. smitinandi (Naiyanetr & Türkay, 1984), T. siamense (A. Milne-Edwards, 1869), and T. varoonphornae Ng & Naiyanetr, 1993 (see Ng et al., 2008). One taxon, Megacephalomon kittikooni (Yeo & Naiyanetr, 1999), originally described under Thaipotamon, was recently reassigned to its own genus by Yeo & Ng (2007). The present study describes a new species from Thailand, here named Thaipotamon holthuisi sp. nov., bringing the number of species in the genus to seven. The following abbreviations are used: G1 and G2 for the male first and second pleopods (gonopods), respectively. Measurements, in millimetres, are of carapace width and length, respectively. Terminology used in the descriptive accounts essentially follows Ng (1988). Material examined is deposited in the Chulalongkorn University Natural History Museum (CUMZ), Bangkok, Thailand, the Zoological Reference Collection (ZRC) of the Raffles Museum of Biodiversity Research, National University of Singapore; and Muséum national d’Histoire naturelle (MNHN), Paris, France. TAXONOMY Family POTAMIDAE Ortmann, 1896 Subfamily POTAMISCINAE Bott, 1970 Thaipotamon holthuisi sp. nov. (figs. 1, 2) Material examined. — Holotype: male, 38.0 by 28.3 mm, ZRC 2002.0101, Wang Yao, Lom Sak District, Phetchabun Province, Thailand, coll. P. Naiyanetr, 29 May 1977. Paratypes: 2 females (larger 50.2 by 38.1 mm) (CUMZ), same data as holotype. Comparative material. — Thaipotamon siamense (A. Milne-Edwards, 1869): lectotype: fe- male, 48.5 by 37.5 mm, MNHN-B.4359S, Bangkok, Siam, coll. Larnaudie, no date; paralecto- type: male, 43.7 by 32.8 mm, MNHN-B.4359S, same data as lectotype. Thaipotamon lomkao Ng & Naiyanetr, 1993: holotype: male, 43.5 by 32.0 mm, ZRC 1991.1873, in burrows made in the soil of an orchard & a forest, Lomkao, Petchabun Province, Thailand, coll. Prasert & Pray- ong, 11 February 1968; paratype: 1 female, 57.7 by 41.6 mm, ZRC 1991.1874, same data as.