Bull. Natl. Mus. Nat. Sci., Ser. A, 45(3), pp. 87–93, August 22, 2019 A New Freshwater Crab of the Genus Flabellamon Ng, 1996 (Crustacea, Decapoda, Brachyura, Potamidae) from Northwestern Thailand Masatsune Takeda1, Oranuch Sanpool2 and Pewpan Maleewong Intapan2 1 Department of Zoology, National Museum of Nature and Science, 4–1–1 Amakubo, Tsukuba, Ibaraki 305–0005, Japan E-mail: [email protected] 2 Department of Parasitology, and Research and Diagnostic Center for Emerging Infectious Diseases, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand E-mails: [email protected] / [email protected] (Received 7 June 2019; accepted 26 June 2019) Abstract A new freshwater crab of the genus Flabellamon Ng, 1996, F. wanchaii, is described from Tak Province, northwestern Thailand. It is a waterfall crab, having the rather flattened dorsal surface of the carapace, the sharp postfrontal and postorbital ridges, and the distinct epibranchial tooth, with general appearance of typical potamid crab, but the male first gonopod is characteristic in having the thickened and curled flap at median to basal part of the inner margin of the terminal segment. Flabellamon wanchaii is the second species of the genus Flabellamon, the type species of which is F. pretzmanni Ng, 1996 by the original designation and now known as F. kuehnelti (Pretzmann, 1963) from Tenasserim in southern Myanmar. Key words: Freshwater crab, Potamidae, Flabellamon, new species, Thailand. Introduction were nomenclaturally nomen nudum or the descriptions were too short and imperfect for During the field survey of freshwater crabs as subsequent identification, but 5 species were val- lung fluke hosts in Tak Province, northwestern idated by Naiyanetr (1992), and 21 species Thailand, the researchers encountered with unfa- described between 1969 and 1992 were clarified miliar crabs living under rock at waterfall in and validated by Ng and Naiyanetr (1993), in mountainous area. The crabs obtained were dis- which 4 new genera of 3 families Potamidae, sected to check the infection of metacercaria lar- Gecarcinucidae and Parathelphusidae were estab- vae of lung flukes, except for only one male crab lished, with 13 new species. Then, many new which was kept for identification. The detailed species were described by Naiyanetr (1993a, b, examination of the specimen revealed that this 1994, 1997, 2001a, b), Ng (1997), Ng & Nai- waterfall crab represents a new species of the yanetr (1995, 1997), Naiyanetr & Ng (1997), Yeo genus Flabellamon Ng, 1996 of the family & Ng (1997), Yeo & Naiyanetr (1999, 2000), Potamidae. Leelawathanagoon et al. (2005, 2010), and Thai freshwater crabs have been taxonomi- Promdam et al. (2014). The family Potamidae cally studied in the late 20th and early 21th cen- from the Southwest Asia was revised by Yeo & turies by Prof. P. Naiyanetr of Chulalongkorn Ng (1997), in which 91 former Potamon s.l. spe- University based on the specimens not only from cies and their allies were re-assigned to 8 known main country but also from the Peninsular prov- and 18 new genera. inces. Some of the new names created by him Naiyanetr (1998) listed 48 species of 11 gen- 88 M. Takeda et al. era in the family Potamidae, 24 species of 7 gen- segment; terminal segment equipped with a era in the family Parathelphusidae and 6 species curled, thickened flap at median to basal part of of 2 genera in the family Gecarcinucidae from inner margin; G2 straight, apparently longer than Thailand. However, as the results of recent stud- G1, weakly curved outward at distal part. ies mentioned above, numbers of the species and Description of holotype. Carapace (Fig. 1A) genera of the Potamidae are increased to 61 spe- transversely ovoid, somewhat narrow in outline; cies of 23 genera (Ng et al., 2008, emended). anterolateral margins regularly convex, cristate, These precedent studies made possible to with a line of close-set granules; dorsal surface describe a new potamid species from mountain- of carapace not convex dorsally, but rather flat- ous, poorly studied area in Tak Province, north- tened as a whole, with weakly deflexed anterior western Thailand. one third, nearly smooth, weakly rugose or scaly In the following lines, the photographs and fig- at anterior part of protogastric region and lateral ures of the holotype male are provided, with their part of branchial region along anterolateral mar- diagnostic and taxonomic notes. The breadth and gin of carapace; protogastric, mesogastric and length of the carapace are abbreviated as cb and cardiac regions weakly demarcated; anterior cl, respectively, and the male first and second inner part of branchial region shallowly gonopods as G1 and G2, respectively. depressed; cervical groove deep between meso- The holotype specimen is deposited at the Tsu- gastric and cardiac regions and along posterolat- kuba Research Departments of the National eral margin of mesogastric region. Frontal mar- Museum of Nature and Science, Tokyo (NSMT). gin (Figs. 1C, 2B) weakly sinuate, shallowly Some of the additional specimens collected in depressed along median part, but not distinctly due time will be sent to the National Science divided into two lobes; frontal and supraorbital Museum of Thailand. margins narrowly thickened, raised, beaded with close-set granules. Frontal region weakly convex dorsally, with 10 or more small depressed gran- Family POTAMIDAE Ortmann, 1896 ules. Epigastric and postorbital ridges of both Genus Flabellamon Ng, 1996 sides markedly strong, sharply cut medially by Flabellamon wanchaii sp. nov. deep furrow of anterior extension of mesogastric (Figs. 1–3) region; each epigastric and postorbital ridges cut Material examined. Tha Song Yang at outside of epigastric region, just behind level (17°32′43″N, 97°56′17″E), Tak Province, Thai- of inner angle of supraorbital margin; postorbital land; 1 ♂ (Holotype, NSMT–Cr 26676; cb crest directly connected with epibranchial tooth; 48.1×cl 35.9 mm), 27 July, 2017. external orbital tooth directed forward, angulated Diagnosis. Waterfall crab, with carapace, at tip, outer margin nearly straight fringed with chelipeds and ambulatory legs of Potamon–Indo- some granules; epibranchial tooth distinct, but chinamon–like appearance. Dorsal surface of not protruded from contour of carapace. Antero- carapace rather flat as a whole, weakly divided lateral margin of carapace (Fig. 1A) behind epi- into regions, granulated at anterolateral parts, branchial tooth narrowly thickened, with poste- with thick epigastric and sharp postorbital ridges, rior part curving shortly onto branchial region; and strong epibranchial tooth; anterolateral mar- more than 20 granules fringing anterolateral mar- gin behind epibranchial tooth regularly convex gin close–set, diminishing size posteriorly. outward, narrowly fringed with a line of gran- Third maxilliped (Fig. 1B) nearly smooth; ules. Exopod of third maxilliped slender, attain- length of ischium twice as long as merus, with a ing to median part of merus, with flagellum equal median longitudinal shallow furrow; merus to breadth of merus. G1 slender, terminal seg- quadrate, antero-inner angle truncated at articula- ment slightly less than one third as long as stem tion with carpus; main surface distinctly flat- New Freshwater Crab from Northwestern Thailand 89 Fig. 1. Flabellamon wanchaii sp. nov., male (cb 48.1×cl 35.9 mm), holotype, NSMT–Cr 26676. A: Habitus in dorsal view. B: Third maxillipeds and pterygostomial regions. C: Frontorbital region in frontal view. D: Abdo- men. E, F: G1 and G2 in situ. tened, surrounded by thickened margins; exopod transverse short line of depressed granules; inner slender, attaining to median part of merus, with surface of merus wholly depressed, smooth; sub- flagellum as wide as merus. marginal linear furrow surrounding distal margin Chelipeds (Fig. 2) heavy, unequal, the right of merus deep. Outer surface of carpus and palm being larger; outer surface of merus scaly, with scaly with transverse lines, depressed granules 90 M. Takeda et al. Fig. 2. Flabellamon wanchaii sp. nov., male (cb 48.1×cl 35.9 mm), holotype, NSMT–Cr 26676. Chelipeds in outer (A) and upper (B) views. and shallow furrows; inner upper angle of carpus the terminal segment is cylindrical and tapering armed with high strong tubercle; lower angle of toward the truncated tip. The G1 terminal seg- carpus shortly tuberculate. Chelae comparatively ment of the new species is, as described above, long; fingers as long as palm, irregularly toothed equipped with a thickened, curled flap at median along whole lengths in both fingers of both che- to basal part of inner margin, differing from the lae, with some teeth larger than most of others. simply extended flap at the basal part of inner Male abdomen (Fig. 1D) seven–segmented, margin seen in such genera as Thaipotamon Ng wide, tapering regularly to lateral median part of & Naiyanetr, 1993, Pudaengon Ng & Naiyanetr, terminal segment, then tapering rapidly toward 1995, and Rathbunomon Ng, 1996. These species rounded tip. G1 (Figs. 1E–F, 2A–B) slender, ter- are the so-called terrestrial or land crabs living in minal segment slightly less than one third as long hole, with thick body, differing from the water- as basal segment; terminal segment equipped fall crab living under stone at waterfall area, with with a thickened, curled flap at median to basal flat body similar to the new species. part of inner margin; G2 (Figs. 1E–F, 2C) In the original definition of the new genus Fla- straight, apparently longer than G1, with distal bellamon, Ng (1996) designated the new species, part weakly curving outward. F. pretzmanni from Tenasserim, Myanmar, as the Color in life. Carapace uniformly dark choc- type species. It was one of the specimens olate brown, with brick red orbital and anterolat- reported by Bott (1970) as Ranguna (Ranguna) eral margins. Upper surfaces of chelipeds and turgidula (Alcock, 1909), but Ng (1996) dis- ambulatory legs pale or grayish chocolate brown. cussed in detail about the taxonomic status of Thoracic sternum, abdomen, outer and inner sur- Potamon turgidulum Alcock, 1909 and P. kue- faces of chelipeds, and under surfaces of ambula- hnelti Pretzmann, 1963. Later, however, Brandis tory legs creamy white. (2002) used Alcockʼs P. turgidulum in the sense Remarks. The new species is seemingly of F. pretzmanni, which has the consequence of close to the species of the genus Potamon s.l. in the synonymy of Potamon kuehnelti and Flabel- the general carapace shape and armature, lamon pretzmanni, and the valid name is F. tur- although the known 22 Thai Potamon species gidula. Brandis (2002) extended the generic were transferred to many known or new genera scope of Flabellamon based on the G2 morphol- by Yeo and Ng (1997) chiefly based on the Gl ogy as described in the following lines.—Termi- structure. Accordingly, it is difficult to refer this nal part dorsoventrally flattened, fused zone of new species to the appropriate genus based only terminal tuber turning one and a half times round on the carapace features. In the new species, axis of terminal tuber; flexible zone short; termi- however, G1 is characteristic and quite different nal tube ending in distinct minutely curved tip. from those of the Potamon s.l. species, in which Brandis (2002) also transferred Potamon turgidu- New Freshwater Crab from Northwestern Thailand 91 Fig. 3. G1 and G2 of Flabellamon wanchaii sp. nov., male (cb 48.1×cl 35.9 mm), holotype, NSMT–Cr 26676. A: Left G1 in sternal (dorsal) view. B: Distal part of left G1 in ventral view. C: Left G2 in ventral view. limana Alcock, 1910, P. pruinosum Alcock, new species, the carapace is slightly more con- 1909, P. kanchanaburiense Naiyanetr, 1992, and vex, uneven and weakly rugose with minute P. erewanense Naiyanetr, 1992 to Flabellamon granules, the external orbital angle and the epi- based only on general agreement in the G2 mor- branchial tooth are less prominent and blunt at phology, but the characters other than G2, espe- the tips, and G1 is slender, with less specialized cially their G1s indicate some essentially differ- terminal segment. In F. kuehnelti, the distal half ent genera. Yeo and Ng (2007) established a new of the G1 terminal segment appears to be sepa- genus Badistemon for Potamon (Potamon) tur- rated from the basal half like a small spearhead. gidulum Alcock, 1909, and the other three spe- The G1 terminal segment of the new species is cies, Potamon turgidulimana, P. pruinosum, P. simple rather than that of F. kuehnelti, but differs kanchanburiense and P. erewanense are known from the further simple flap of the species of the at present as the species of the genus Stelomon genera other than Flabellamon. Yeo & Naiyanetr, 2000. Etymology. This species is named after Prof. The monotypic species of the genus Flabella- Wanchai Maleewong of Khon Kaen University mon, F. pretzmanni Ng, 1996, which is currently for his kind guidance and encouragements during considered as a junior synonym of F. kuehnelti the studies of lung fluke parasitology in Thai- (Ptetzmann, 1963), was well represented by land. Pretzmann (1963, as Potamon kühnelti), Ng (1996, as Flabellamon pretzmanni) and Brandis (2002, as Flabellamon turgidula). In the present 92 M. Takeda et al. Acknowledgements new freshwater crab from Thailand (Decapoda, Brachyura, Potamidae). Crustaceana, 65: 1–7. Naiyanetr, P. 1994. On two species of terrestrial crabs of The authors wish to thank Dr. Peter K. L. Ng the genus Dromothelphusa Naiyanetr, 1992 (Crustacea: of the Lee Kong Chian Natural History Museum, Decapoda: Brachyura: Potamidae) from Thailand. Raf- Faculty of Science, National University of Singa- fles Bulletin of Zoology, 42: 689–694. pore, for his suggestion about the genus to which Naiyanetr, P. 1997. Dromothelphusa sangwan n. sp., a new freshwater crab from Thailand (Decapoda, the new species was referred. Drs. Hiroshi Yama- Brachyura, Portamidae). Crustaceana, 70: 385–393. saki and Hiromu Sugiyama of the Department of Naiyanetr, P. 1998. Checklist of Crustacean Fauna in Parasitology, National Institute of Infectious Dis- Thailand (Decapoda and Stomatopoda). OEPP (Office eases, Tokyo, for their arrangement of the speci- of Environmental Policy and Planning, Ministry of Sci- men for study. Field survey for freshwater crabs ence Technology and Environment) Biodiversity Series, 5: 161 pp. as intermediate hosts of lung flukes was sup- Naiyanetr, P. 2001a. Potamon bhamibol n. sp., a new ported by the Distinguished Research Professor giant freshwater crab from Thailand (Decapoda, Grant, Thailand Research Fund (Grant no. DPG Brachyura, Potamidae). Crustaceana, 74: 309–316. 6280002) to Prof. Wanchai Maleewong of Khon Naiyanetr, P. 2001b. Potamon galyaniae n. sp., a new Kaen Univerity. fereshwater crab from Thailand (Decapoda, Brachyura, Potamidae). Crustaceana, 74: 401–405. Naiyanetr, P. and P. K. L. Ng 1997. Esanpotamon nam- References som, a new genus and species of potamid crab (Crusta- cea: Decapoda: Brachyura) from a waterfall in north- Alcock, A. 1909. Diagnoses of new species and varieties eastern Thailand. Proceedings of the Biological Society of freshwater crabs. Nos. 1–3. Records of the Indian of Washington, 110: 417–421. Museum, 3: 243–252. Ng, P. K. L. 1996a. Establishment of two new genera for Alcock, A. 1910. Catalogue of the Indian Decapod Crus- Potamon lacunifer Rathbun, 1904, and Potamon lao- tacea in the Collection of the Indian Museum. Part I. sensis Rathbun, 1904 (Decapoda, Brachyura, Potami- Brachyura. Fasciculus II. The Indian Fresh-water Crabs dae) from Laos. Crustaceana, 69: 898–906. ーPotamonidae. Calcutta: Printed by Order of the Ng, P. K. L. 1996b. On a new genus and new species of Trustees of the Indian Museum, 135 pp., 14 pls. potamid crab (Brachyura) from Burma. Crustaceana, Bott, H. 1970. Die Süßwasserkrabben von Europa, Asien, 69: 1005–1013. Australien und ihre Stammesgeschichte. Abhandlungen Ng, P. K. L. 1997. On two new species of Sayamia and der Senckenbergischen Naturforschenden Gesellschaft, Heterothelphusa from southern Thailand. Crustaceana, 526: 1–338. 70: 710–719. Brandis, D. 2002. On the taxonomic status and biogeogra- Ng, P. K. L., D. Guinot and P. J. F. Davie 2008. Systema phy of the Isolapotamidae Bott, 1970 (Decapoda, Brachyurorum: Part I. Annotated checklist of extant Brachyura). Journal of Natural History, 36: 1291–1339. brachyuran crabs of the world. The Raffles Bulletin of Leelawathanagoon, P., V. Lheknim and P. K. L. Ng 2005. Zoology, 17: 1–286. On a new species of freshwater crab of the genus Ng, P. K. L. and P. Naiyanetr 1993. New and recently Johora (Brachyura, Potamidae) from Peninsular Thai- described freshwater crabs (Crustacea: Decapoda: land. Crustaceana, 78: 59–66. Brachyura: Potamidae, Gecarcinucidae and Parathel- Leelawathanagoon, P., V. Lheknim and P. K. L. Ng 2010. phusidae) from Thailand. Zoologische Verhandelingen, On a new species of freshwater crab of the genus Ter- 284: 1–117. rapotamon (Brachyura, Potamidae) from Peninsular Ng, P. K. L. and P. Naiyanetr 1995. Pudaengon, a new Thailand. Crustaceana, 81: 49–59. genus of terrestrial crabs (Crustacea: Decapoda: Naiyanetr, P. 1992. Validation of five new species of Thai Brachyura: Potamidae) from Thailand and Laos, with potamid crabs (Crustacea: Decapoda: Brachyura). Raf- descriptions of seven new species. Raffles Bulletin of fles Bulletin of Zoology, 40: 1–7. Zoology, 43: 355–376. Naiyanetr, P. 1993a. Two new species of terrestrial crabs Ng, P. K. L. and P. Naiyanetr 1997. A revision of the of the genus Potamon Savigny, 1816 from Thailand genus Siamthelphusa Bott, 1968 (Crustacea: Decapoda: (Decapoda: Potamidae). International Senckenberg Brachyura: Parathelphusidae), with descriptions of five Symposium, Crustacea Decapoda, Abstract Volume, p. new species from Thailand. Journal of Natural History, 44. 31: 1751–1784. Naiyanetr, P. 1993b. Thaipotamon chulabhorn n. sp., a Pretzmann, G. 1963. Über einige süd- und ostasiatische New Freshwater Crab from Northwestern Thailand 93 Potamoniden. Annalen des Naturhistorischen Museums species. Journal of Natural History, 34: 1625–1637. Wien, 66: 361–372. Yeo, D. C. J., P. Naiyanetr and P. K. L. Ng 1999. Revision Promdam, R., J. Nabhitabhata and P. K. L. Ng 2014. of the waterfall crabs of the genus Demanietta (Deca- Nakhonsion ramromensis, a new genus and species of poda: Brachyura: Potamidae). Journal of Crustacean freshwater crab (Crustacea: Decapoda: Brachyura: Biology, 19: 530–555. Potamidae) from Nikhon Si Thammarat, Peninsular Yeo, D. C. J. and P. K. L. Ng 1997. On a new genus of Thailand. Raffles Bulletin of Zoology, 62: 496–500. riverine crab (Crustacea: Decapoda: Brachyura: Yeo, D. C. J. and P. Naiyanetr 1999. Three new species of Potamidae) from northwestern Thailand, with descrip- freshwater crabs from northern Laos, with a note on tions of two new species. Hydrobiologia, 350: 179– Potamiscus (Ranguna) pealianoides Bott, 1966 (Crus- 188. tacea, Decapoda, Brachyura, Potamidae). Zoosystema, Yeo, D. C. J. and P. K. L. Ng 2007. On the genus “Pota- 21: 483–494. mon” and allies in Indochina (Crustacea: Decapoda: Yeo, D. C. J. and P. Naiyanetr 2000. A new genus of Brachyura: Potamidae). The Raffles Bulletin of Zool- freshwater crab (Crustacea: Decapoda: Brachyura: ogy, Supplement, 16: 273–308. Potamidae) from Thailand, with a description of a new