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Le, Van Tu Do Van Tho, Phan, Doan Dang (2015): Binhthuanomon vinhtan, a new genus and new species of semi-terrestrial freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from south central Vietnam. Zootaxa 4052 (1): 117-126, DOI: http://dx.doi.org/10.11646/zootaxa.4052.1.6

Binhthuanomon vinhtan sp. nov. (Figs. 2 ���4, 6) Material examined. Holotype: male (53.9 �� 42.9 mm) (ITB-FC PNx01), 11 �� 22 ' 50.5 "N 108 �� 47 '49.0"E, Nui Chua, Vinh Tan commune, Tuy Phong district, Binh Thuan Province, Vietnam, 700 m, coll. Phan Doan Dang & Le Van Tho, July 2014. Paratypes: 6 male (51.3 40.0 mm, 50.5 �� 40.0 mm, 47.0 �� 37.0 mm, 46.0 �� 37.0 mm, 41.0 �� 32.0 mm, 35.0 �� 28.0 mm) (ITB-FC PNx02-07), 3 female (37.0 �� 29.5 mm, 34.3 25.7 mm, 23.8 18.8 mm) (ITB-FC PNx08- 10), same data as holotype. Comparative material. Villopotamon thaii Dang & Ho, 2003: Holotype, male (54.5 �� 40.2 mm) (IEBR), stream at Ba Na (Quang Nam province), Vietnam, coll. unknown, 20 April 2002. Paratypes: 1 male (50.9 �� 38.2 mm), 2 females (larger 40.6 �� 35.6 mm) (IEBR), same data as holotype. Balssipotamon ungulatum (Dang & Ho, 2003): Holotype, male (57.9 �� 44.8 mm) (IEBR), stream at Ninh Hai (Ninh Phuoc District, Ninh Thuan Province), Vietnam, coll. unknown, 29 September 2002. Paratypes: 1 male (52.0 �� 39.4 mm), 1 female (55.0 �� 41.3 mm) (IEBR), same data as holotype. Laevimon kottelati Yeo and Ng, 2005: male (45.4 �� 31.9 mm) (IEBR-FC LKx01), 20 �� 46 ' 58.5 "N 107 ��0' 1.8 "E, unnamed small stream near Trung Trang cave, Ca Ba island, Hai Phong, Vietnam. Hainanpotamon rubrum (Dang & Tran, 1992): male (22.6 �� 16.8 mm) (IEBR-FC HRx01), Xuan Son National Park, Phu Tho, Vietnam. Description. Carapace distinctly transverse, about 1.26 times broader than long (n = 10), high; dorsal surface strongly inflated, swollen vertically, laterally, glabrous; regions poorly defined, cervical grooves undiscernible, Hshaped depression shallow but distinct (Figs. 2 A, 3 A). Epigastric cristae poorly developed, rounded, smooth, confluent with postorbital cristae; postorbital cristae poorly developed, straight, rounded, smooth; regions behind epigastric, postorbital cristae smooth (Figs. 2 A, 3 A). Frontal margin broadly emarginate medially; frontal region strongly deflected downward, smooth; antennular fossae slit-like when viewed from frontal view; orbital region very narrow, smooth; supraorbital margin very gently sinous, cristate; infraorbital margins cristate, almost straight; orbital region smooth, relatively narrow; eyes normally developed; subhepatic, subbranchial regions smooth (Figs. 2 A, B). External orbital angle low but distinct, triangular, smooth; epibranchial tooth indistinct, separated from external orbital angle by wide cleft; anterolateral margin convex, smooth; posterolateral margin rounded, not convergent posteriorly; branchial region smooth, inflated; metabranchial region almost smooth, with faint oblique striae (Figs. 2 A, B). Epistome anterior margin with median triangle; posterior margin with low median triangular tooth, slightly crenulated, with outer part slightly concave (Fig. 2 B). Third maxilliped glabrous; ischium rectangular, about 1.67 times longer than broad, with distinct longitudinal median sulcus; merus squarish, longer than half (0.54 times) of ischium length, with concave outer surface; palp normal with tip exceeding proximal margin of merus; exopod relatively long, exceeding upper edge of ischium, exceeding proximal margin of merus, distally tapered, blunt tooth on distal part of inner margin weakly developed, with short but distinct flagellum, slightly longer than half width (0.63) of merus (Figs. 2 B, 3 C). Ambulatory legs normal, glabrous, relatively slender; dactyli elongated, slender; merus unarmed with upper margin weakly serrated; in second pair dactylus about 6.56 times longer than proximal width, propodus about 2.71 times longer than broad, about 0.83 times length of dactylus, carpus about 0.76 times length of dactylus, merus about 1.41 times longer than dactylus (n = 4); fourth pair with dactylus about 6.19 times longer than proximal width, propodus about 0.88 times length of dactylus, carpus about 0.81 times length of dactylus, merus about 3.04 times longer than proximal width, about 1.34 times longer than dactylus (n = 4) (Fig. 2 A). Suture between anterior thoracic sternites 2, 3 complete, distinct, straight; groove between sternites 3, 4 distinct, broad, not fused with tip margin of abdominal cavity (Fig. 2 C); thoracic sternites 5, 6 medially interrupted; sternites 7, 8 medially separated by distinct longitudinal median suture. Male abdominal cavity reaching imaginary line joining middle points of cheliped bases (at sternite 4) (Fig. 2 D). Tubercles of male abdominal-locking mechanism positioned in thoracic sternite 5. Male abdomen broadly triangular; telson narrowly triangular, broader than long, lateral margins deeply concave, tip rounded, subequal in length to sixth segment; segment 6 with proximal width about 2.29 times length, lateral margins gently convex; lateral margins of segments 4 to 5 straight; lateral margins of segment 3 gently convex (Figs. 2 C, 3 B). Gl sinuous, distinctly sinuous (Fig. 2 D); terminal segment slender, tapered, about 0.26 times length of subterminal segment, about 2.82 times longer than proximal width, without dorsal flap, sparsely covered by pubescence in ventral side, groove for accommodation of G 2 marginal; subterminal segment relatively slender, sinuous, without neck-like distal part, subdistal cleft or shelf on outer margin (Figs. 4 A���H). G 2 equal or slightly longer than G 1 with distal segment shorter than half length of basal segment (Figs. 4 I���J). Etymology. The new species is named after the type locality, Vinh Tan. The name is used as a noun in apposition. Coloration. Carapace, abdomen and ambulatory legs reddish brown, chelipeds with magenta color. Ecological notes. This species inhabits forested mountain areas (Figs. 5 A���C). The crabs were found living in vertical burrows, beneath large rocks or under fallen trees, near one stream bank (Figs. 6 A, B). Few individuals wer also found in the stream, however. It is believed that this species spends almost all of their time in terrestrial environments. Indeed, the more terrestrial habit is usually associated with freshwater crabs with a high and swollen carapace (Yeo & Ng, 2005). The crabs are usually active in the evening until early morning. In the evening, the stream area is usually covered by fog and therefore very humid. It is very difficult to find the crabs in the dry season. The best time to collect them is during the rainy season, especially after heavy rain. The crabs feed primarily on insects and plants along streams. Remarks. This species is found only in limited numbers in and around one small stream, 800 m in length, located in south central Vietnam. It could not be found in other regions around this area (north central and Central Highlands of Vietnam) during our surveys. We believe this species has a small distribution area. The area of occupancy is not part of any protected area and is strongly impacted by deforestation. Local people sometime catch these crabs for food; however, it is only when they accidentally collect them. Therefore, this species should be considered endangered due to limited range and impacts of deforestation on the IUCN Red List Categories and Criteria (IUCN, 2001)., Published as part of Le, Van Tu Do Van Tho & Phan, Doan Dang, 2015, Binhthuanomon vinhtan, a new genus and new species of semi-terrestrial freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from south central Vietnam, pp. 117-126 in Zootaxa 4052 (1) on pages 118-126, DOI: 10.11646/zootaxa.4052.1.6, http://zenodo.org/record/237939, {"references":["Dang, N. T. & Ho, T. H. (2003) Two new potamid crab species of Potamidae from southern part of Vietnam. Journal of Biology, 25 (3), 7 - 13. [in Vietnamese].","Yeo, D. C. J. & Ng, P. K. L. (2005) On a new genus and species of freshwater crab from Vietnam, with comments on the nomenclatural status of Orientalia Dang, 1975 (Crustacea: Brachyura: Potamidae: Potamiscinae). Zootaxa, 917, 1 - 15."]}

Genus Binhthuanomon, n. gen. Type species. Binhthuanomon vinhtan, new species, by present designation Diagnosis. Carapace distinctly transverse, high, dorsal surface strongly convex transversely, longitudinally, surfaces conspicuously smooth, grooves weak to indistinct, regions poorly defined; epigastric, postorbital cristae not separated, indistinct, rounded, smooth; postorbital cristae close to supraorbital margins; postorbital regions narrow; frontal margin strongly deflexed downwards, appears narrow from dorsal view; anterolateral margin rounded, smooth; epibranchial tooth poorly developed, almost absent; external orbital angle low but distinct, triangular. Flagellum of exopod of third maxilliped short, tip blunt, slightly longer than half width of merus. Male abdomen broadly triangular. Male telson with lateral margins concave. G 1 sinuous; terminal segment slender, tapered, sinuous without dorsal fold, about 0.26 times length of subterminal segment. G 2 with distinct distal segment, shorter than half length of basal segment, basal segment with outer margins slightly convex. Etymology. The genus is named after the location, the province of Binh Thuan, in combination with the genus name Potamon. The gender is neuter. Remarks. The general carapace shape and G 1 of the new genus are superficially similar to Balssipotamon ungulatum (Dang & Ho, 2003), and Villopotamon thaii Dang & Ho, 2003. It can nevertheless be easily distinguished from these two species by the following characteristics: 1) carapace is high, much inflated and swollen (relatively flat carapace in Balssipotamon and Villopotamon); 2) H-shaped depression is shallow (Hshaped depression deep in the two genera); 3) epigastric and postorbital cristae are indistinct (epigastric and postorbital cristae distinct, sometimes sharp in the two genera); 4) postorbital cristae is close to supraorbital margins (postorbital cristae not close to supraorbital margins in the two genera); 5) postorbital regions are very narrow (postorbital regions slightly narrow or wide in the two genera); 6) anterolateral margin is rounded and smooth (anterolateral margin sharp and serrated in the two genera); 7) epibranchial tooth is poorly developed, almost absent (epibranchial tooth poorly developed but visible in the two genera); 8) external orbital angle is low (external orbital angle not low in the two genera); 9) groove between sternites 3 and 4 is deep (groove between sternites 3 and 4 shallow in the two genera); 10) lateral margins of telson are concave (lateral margins of telson almost straight in the two genera); and 11) G 1 is sinuous (strongly sinuous in Villopotamon or slightly sinuous in Balssipotamon), with terminal segment slender (terminal segment more slender, sinuous and elongated in Villopotamon or stout and short in Balssipotamon). Moreover, the new genus lives in semi-terrestrial habitats, whereas Villopotamon and Balssipotamon occupy freshwater habitats. Dang & Ho (2003) established a new genus, Villopotamon, for a new species, Villopotamon thaii Dang & Ho, 2003. Yeo & Ng (2007) subsequently included four more species in the genus, all formerly in Potamon sensu lato (Yeo & Ng, 1999; Dang & Ho, 2003), viz., V. frushstorferi (Balss, 1914), V. klossianum (Kemp, 1923), and V. ungulatum (Dang & Ho, 2003). Dang & Ho (2008) identified a new genus, Balssipotamon, and compared it with Villopotamon. The new genus Balssipotamon included two species, B. ungulatum (Dang & Ho, 2003), and B. fruhstorferi (Balss, 1914) (Dang & Ho, 2008, 2012). Recently more specimens collected from many localities of southern Vietnam showed a high similarity between these genera in terms of the morphology of the carapace and G 1 structures. Further studies are required to clarify the relationship between the two genera. Binhthuanomon is also superficially similar with Hainanpotamon Dai, 1995, and Laevimon Y eo & Ng, 2005, owing to its high, swollen, and smooth carapace, and the long, slender ambulatory dactyli. Binhthuanomon can nevertheless be distinguished from Hainanpotamon and Laevimon by the following characteristics: 1) suture between sternites 3 and 4 distinct, broad (not discernible in Hainanpotamon or by a distinct, strong ridge in Laevimon; and 2) G 1 terminal segment filiform, long, without proximal dorsal flap (terminal segment conical in Hainanpotamon or subcylindrical in Laevimon. with proximal dorsal flap)., Published as part of Le, Van Tu Do Van Tho & Phan, Doan Dang, 2015, Binhthuanomon vinhtan, a new genus and new species of semi-terrestrial freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from south central Vietnam, pp. 117-126 in Zootaxa 4052 (1) on page 118, DOI: 10.11646/zootaxa.4052.1.6, http://zenodo.org/record/237939, {"references":["Dang, N. T. & Ho, T. H. (2003) Two new potamid crab species of Potamidae from southern part of Vietnam. Journal of Biology, 25 (3), 7 - 13. [in Vietnamese].","Yeo, D. C. J. & Ng, P. K. L. (2007) On the genus \" Potamon \" and allies in Indochina (Crustacea: Decapoda: Brachyura: Potamidae). The Raffles Bulletin of Zoology, Supplement No. 16, 273 - 308.","Yeo, D. C. J. & Ng, P. K. L. (1999) The state of freshwater crab taxonomy in Indochina (Decapoda, Brachyura). In: F. R. Schram & J. C. v. Vaupel Klein (Eds), Crustaceans and the biodiversity crisis. Proceedings of the Fourth International Crustacean Congress, Amsterdam, The Netherlands, July 20 - 24, 1998. Brill, Leiden, pp. 637 - 646.","Dang, N. T. & Ho, T. H. (2008) On the taxonomy of freshwater crabs allied to the genus Potamon (Potamidae) in Vietnam. Journal of Biology, 30 (2), 12 - 17."]}