Freshwater crabs of Thailand

Abstract

                               Sixteen  species of freshwater crabs fromThailandwere identified and rearranged in their  classification discriminating mostly on the structures of the first gonopod by Bott (1970).

                                Freshwater crabs had been studied earlier by Rathbun (1904-1906), Alcock (1909, 1910) and  others. Kemp (1923) reported only 5 species of river crabs found inThailand. Recently, Bott (1970) rearranged the classification of freshwater crabs using the structures of the first gonopod as the discriminating taxa and reported 14 species fromThailandin his publication.

                                Observation of freshwater crabs in the collection of the Museumof Fisheries, KasetsartUniversity, Bangkok, Thailandrevealed that the changing from Ranguna (Ranguna) siamensis, (BOTT, 1970) to Ranguna (Demanietta) siamensis is taxonomically logical. A new subspecies of Ranguna (Demanietta)tenasserimensis fromThailand was also described.

                                The sixteen species of freshwater crabs belonging to two families (Parathelphusidae and Potamidae) were studied and described.

                                Carapace width : carapace length : carapace thickness : front width were measured in mm. All gonopods were from the right hand side and in order to avoid confusion, the following terms were used in this paper for the first gonopod :

                                (1)  Basal = proximal,

                                (2)  Channel = a longitudinal groove formed laterally on the distal and predistal segments,

                                (3)  Distal segment = the last segment at the distal end,

                                (4)  Dorsal portion = the surface area on the distal segment inwhich in contact with the sternum of the crab. Smalley (1964) named it as ‘cephalic surface’,

                                (5)  Predistal segment = the segment between distal segment and basiopodite or the last but one segment at the distal end, and

                                (6)  Ventral portion = the surface area on the distal segment which could be seen directly when the abdomen was opened. Smalley (1964) named it the ‘caudal surface’.

                                Abbreviations in text are :

                                Go-1                      first gonopod,

                                Go-2                      second gonopod,

                                KUMF                  KasetsartUniversity,MuseumofFisheries,Bangkok,

                                MLei                      Rijksmuseum van Natuurlijke Historie Leiden,

                                MHa                       Zoologisches Staatsinstitut undZoologisches MuseumHamburg,

                                MPa                       Muséum d’Histoire NaturelleParis

                                MWa                     USNational MuseumWashington, USNM.

                                Mxp-3                   third maxilliped,

                                P-1                         first pereiopod or chelae,

                                P-5                         fifth pereiopod or last walking leg,

                                P2-5                       second to fifth pereiopods, and

                                SMF                      SenckenbergMuseumFrankfurt amMain.