The identity of the common lowland freshwater crab in western Sarawak, Borneo, East Malaysia, Parathelphusa oxygona Nobili, 1901 (family Gecarcinucidae), is clarified. The species is redescribed and figured, and its taxonomy discussed. Specimens from western Kalimantan, Borneo, Indonesia, which have been referred to P. oxygona are here referred to a new species, Parathelphusa nobilii. The new species can be differentiated from congeners by its relatively more swollen branchial regions of the carapace, wider and lower external orbital tooth, relatively more slender male abdomen and a straight male first gonopod.
A new species of terrestrial sesarmid crab, Scandarma raymondi, is described from Sabah, Malaysia. This is the third species in the genus; others are from Taiwan, Japan and Sarawak, Borneo. The new species differs from congeners in the live coloration, proportions of the carapace and ambulatory legs and morphologies of the male abdomen, chela and male first gonopod.
The taxonomy of the potamid freshwater crabs of the Johora tahanensis (Bott, 1966) species group (Potamoidea) is revised. Seven species are recognised, all from Peninsular Malaysia and southern Thailand, three of which are described as new. The three new species were previously identified as J. tahanensis but can be distinguished by characters of the carapace, male first gonopod, and vulva. A revised key to the 18 recognised species of Johora Bott, 1966, is provided.
A new species of semi-terrestrial crab of the genus Geosesarma (Sesarmidae) is described from a limestone cave in central Sarawak, Malaysian Borneo. Geosesarma sodalissp. nov. is characterised by its quadrate carapace, absence of a flagellum on the exopod of the third maxilliped, presence of 10 or 11 sharp tubercles on the dactylus of the chela and a diagnostic male first gonopod structure. This is the sixth species of Geosesarma reported from Sarawak, and the first member of the genus collected from inside caves.
Two new species of the gecarcinucid freshwater crab genus Arachnothelphusa are described from the Malaysian state of Sarawak in Borneo; one from Lanjak-Entimau Wildlife Sanctuary and another from Bako National Park. Arachnothelphusa rimba n. sp. is distinctive in possessing very long legs and a male first gonopod which has a cylindrical proximal part of the terminal segment, with the distal part sharply tapering to an acute tip. Arachnothelphusa bako n. sp. is superficially closest to A. kadamaiana from Sabah, but differs markedly by its narrower epistome, and proportionately shorter third maxillipeds and ambulatory legs.
A new species of lowland freshwater crab of the family Gecarcinucidae, Salangathelphusa peractio, is described from Langkawi, an island off the northwestern coast of peninsular Malaysia. Salangathelphusa peractiosp. n. can be separated from S. brevicarinata (Hilgendorf, 1882) in having a proportionately broader external orbital tooth, a distinctly concave posterolateral margin, and the terminal segment of the male first gonopod is not distinctly bent laterally outwards; and from S. anophrys (Kemp, 1923) by its more quadrate carapace and the terminal segment of the male first gonopod possessing a relatively longer and less curved distal part. This is sixth wholly freshwater brachyuran species known from the island.
A new species of cave crab, Stygothelphusa antu new species, is described from limestone formations in Temurang, Sarawak, Malaysia. The new species is the most highly adapted to a cavericolous lifestyle among the four known species of Stygothelphusa, having a pale body pigmentation, reduced eyes and elongated pereopods. In contrast, the other three species have normal eyes that almost completely fill the orbits. The new species also differs from its congeners by a number of carapace, pereopod and gonopod characters.
The male of Hexapinus latipes (De Haan, 1835), so far known only from female specimens, is described based on the material reported by De Man (1888) as "Hexapus sexpes". Material referred to "Hexapus sexpes" by Tesch (1918) is shown instead to belong to Hexapinus simplex Rahayu & Ng, 2014, and Hexapinus latus Rahayu & Ng, 2014, while his "Hexaplax megalops Doflein, 1904" belongs to Hexaplax aurantium Rahayu & Ng, 2014. A new species, Mariaplax aspera n. sp., is described from a female collected in Lombok, Indonesia. This new species most closely resembles M. narusei Rahayu & Ng, 2014, described from Japan, but differs by its relatively narrower carapace, shorter ambulatory legs, tuberculated third maxillipeds, and shorter telson.
Four new species of semiterrestrial gecarcinucid crabs are described from limestone and sandstone habitats in southwestern Sarawak, Malaysia: Terrathelphusa aglaia n. sp., T. cerina n. sp., T. kundong n. sp., and T. mas n. sp. The taxonomy of T. kuchingensis (Nobili, 1901) is discussed, its precise identity ascertained from fresh material, and its actual distribution determined. This increases the number of Terrathelphusa species in Borneo to eight.
Three new Indo-West Pacific species of pinnotherid crabs are described, one each of Arcotheres, Buergeres and Nepinnotheres. Arcotheres pollus, described from Paway Island, Mergui Archipelago, is most similar to A. boninensis (Stimpson, 1858), A. pernicola (Bürger, 1895) and A. purpureus (Alcock, 1900), sharing a transversely ovate carapace and long, slender, almost styliform dactyli of P4 and 5 that are about twice the length of those of P2 and 3. Buergeres choprai, described from Papua New Guinea, is most similar to B. deccanesis (Chopra, 1931) from eastern India but differentiated by segment proportions and setation of the walking legs. Buergeres tenuipes (Bürger, 1895) is synonymised with B. ortmanni (Bürger, 1895), which is also reported for the first time from Indonesia. A male of an undetermined species of Buergeres from the Philippines, possibly B. ortmanni, is figured and described, documenting the gonopod morphology in Buergeres for the first time. A key to the species of Buergeres based on females is provided. Nepinnotheres fulvia sp. nov. is also described from Papua New Guinea, and resembles N. cardii (Bürger, 1895) from the Philippines and Malaysia but can be distinguished by features of the chelipeds and maxilliped 3.
A new species of the porcellanid genus Raphidopus Stimpson, 1858, is described on the basis of specimens from Penang and Kuala Selangor, Peninsular Malaysia. Raphidopus brevipes n. sp. is distinguished from its allied congeners, R. indicus Henderson, 1893 and R. johnsoni Ng Nakasone, 1994, by the proportionally narrower carapace and stouter ambulatory legs, as well as the different dentition on the cutting edge of the dactylus of the larger cheliped. Raphidopus johnsoni, previously known only by the holotype from Singapore, is now also recorded from Phuket (Thailand) and Java (Indonesia). Raphidopus indicus and R. johnsoni are rediagnosed on the basis of the respective type material and other specimens. A key to species of the genus Raphidopus is provided.
A new species of semiterrestrial highland vampire crab of the family Sesarmidae, Geosesarma larsi n. sp., is described from western Sarawak. This brings the number of Bornean Geosesarma species to 12. Geosesarma larsi n. sp. is distinguished from congeners by the structures of the carapace, third maxilliped exopod and gonopods, as well as the proportions of its ambulatory legs. The colour pattern in life is also strikingly different from allied species. Notes on its ecology are provided and conservation threats briefly discussed.
The gecarcinucid freshwater crab genus, Lepidothelphusa Colosi, 1920, is known only from Sarawak in northern Borneo, with six recognised species i.e. Lepidothelphusa cognettii (Nobili, 1903); L. flavochela Grinang & Ng, 2015; L. limau Grinang & Ng, 2015; L. loi Grinang & Ng, 2015; L. padawan Grinang & Ng, 2015; and L. sangon Grinang & Ng, 2015. The genus is now reported from Indonesian Borneo for the first time, from specimens recently collected from Gunung Kelam in Sintang Regency, Kalimantan Barat Province. Lepidothelphusa menneri n. sp. has a very distinctive tri-coloured pattern in life, unique among congeners. It can also easily be separated from congeners by carapace, epistome, male pleonal and male first gonopod characters.
A new species of semiterrestrial gecarcinucid freshwater crab, Terrathelphusa secula, is described from Danum Valley in Sabah, East Malaysia, eastern Borneo. In the form of its carapace, third maxilliped, and male second gonopod, it most closely resembles T. ovis Ng, 1997, and T. telur Ng, 1997, from eastern Sarawak and Brunei, respectively. It differs markedly from these and other congeners in its proportionately much wider carapace, and a male first gonopod that is strongly curved and sickle-shaped.
The pinnotherid crab, Pinnothera obesa Dana, 1852, was originally described on the basis of material from Fiji, but its taxonomic status has long been obscure because the original description and figures are too brief and schematic by modern standards and the types are also lost. Examination of newly collected material from Fiji revealed the presence of two intertidal pinnotherid species assignable to the genus Arcotheres Manning, 1993, one of which is herein identified with Dana's taxon. A neotype is designated for Arcotheres obesus n. comb. in the interest of nomenclatural stability, and a detailed redescription is given. Arcotheres obesus is morphologically similar to A. exiguus (Bürger, 1895) and A. rotundatus (Bürger, 1895), and differentiating characters are discussed. The species is also reported from Peninsular Malaysia. The second species is new to science, here described as Arcotheres ocularius, and is most similar to A. palaensis (Bürger, 1895) and A. arcophilus (Bürger, 1895). The new species is also recorded from Lombok, Indonesia. Arcotheres obesus and A. ocularius n. sp. are associated with bivalve mollusks of the genera Gafrarium spp. (Veneridae) and Anadara spp. (Arcidae), respectively.
A new species of gecarcinucid freshwater crab of the genus Parathelphusa H. Milne Edwards, 1853, is described from freshwater swamp habitats in Pekanbaru, Riau Province, in central-eastern Sumatra, Indonesia. Parathelphusa pardus sp. nov., has a very distinctive colour pattern, and in this respect, resembles P. maindroni (Rathbun, 1902) from Sumatra and Peninsular Malaysia; P. batamensis Ng, 1992, from Batam Island, Indonesia; P. reticulata Ng, 1990, from Singapore; and P. oxygona Nobili, 1901, from western Sarawak. It can be distinguished from these species and congeners by a suite of carapace, ambulatory leg, thoracic sternal and most importantly, male first gonopod characters.
Seven species of freshwater crabs from three families are recorded from and around the Danum Valley Conservation Area in Sabah, Malaysian Borneo: Thelphusula capillodigitussp. n., Thelphusula dicerophilus Ng & Stuebing, 1990, Arachnothelphusa terrapes Ng, 1991, Terrathelphusa secula Ng & Tan, 2015, Parathelphusa valida Ng & Goh, 1987 (new record) (Gecarcinucidae); Isolapotamon ingeri Ng & Tan, 1998 (Potamidae); and Geosesarma danumense Ng, 2002 (Sesarmidae). The new species of Thelphusula Bott, 1979, can be distinguished from all congeners by a unique combination of morphological features, most notably the presence of dense patches of short setae on the fingers of the adult male chelipeds, as well as the structure of the male first gonopod. Arachnothelphusa terrapes is confirmed to be a phytotelm species. A key to all species in the conservation area is provided.
Five species of the genus Polyonyx Stimpson, 1858 are reported from southern Japan, the Philippines, Singapore, and Peninsular Malaysia. All of them belong to the P. sinensis group, which is morphologically defined by having the dactyli of the ambulatory legs each with the dorsal claw being much smaller than the ventral claw. Two species are described as new to science, one each from Peninsular Malaysia and the Ryukyu Islands in Japan, and their affinities are discussed. Polyonyx boucheti Osawa, 2007, P. heok Osawa Ng, 2016, and P. thai Werding, 2001, are also newly reported from southern Japan, the Philippines, and Singapore. A key to the Indo-West Pacific species of the P. sinensis group is provided.
The taxonomy of freshwater crabs requires a paradigm change in methodological approaches, particularly in investigations that use morphological techniques. The traditional morphometric approach (two-dimensional measurements) tends to be inappropriate for the identification of freshwater crabs due to their variable external morphology and lack of gonopods (conventionally used for the identification of male crabs) in females. In this study, we explore the potential use of the geometric morphometric technique for identification of female freshwater crabs, and identify taxonomic key characteristics of species. The shape of the carapace could be a good characteristic for the identification of female crabs, especially when the geometric morphometric technique is used. It was observed that the shape of the carapace has an advantage over the shape of the pleon and chela because its relatively flat orientation allows more consistent and easier data preparation for geometric morphometric analysis. The geometric morphometric technique is inexpensive, relatively less time consuming to employ, and accurate. This technique is convenient when dissection to examine the gonopods is not possible, which can damage the specimen in the case of endangered or rare species. Since the technique was used herein for only two species, more compelling and extensive evidence is needed before the reliability of the method can be proven.