A new genus and three new species of freshwater crab (Crustacea: Brachyura: Potamidae) from central and northern Vietnam Author Ng, Peter K. L. Author Tri, Ngo Van text Raffles Bulletin of Zoology 2023 2023-02-03 71 70 86 journal article 10.26107/RBZ-2023-0005 2345-7600 7815677 BA361B52-E36A-4C15-AB6B-FECA9CEF58AF Indochinamon lanae , new species ( Figs. 6A–D , 8 , 10A–E, K , 11A–D ) Material examined. Holotype : male (39.0 × 30.0 mm) ( ZRC 2022.0049 ), small stream, branch of Ba Che River , Don Dat commune, Ba Che Town , Quang Ninh Province , northeastern Vietnam , 21°13′4.50″N 107°16′26.05″E , coll. V . T . Ngo , 15 March 2022 . Paratype : juvenile female (16.8 × 13.5 mm ) ( ZRC 2022.0050 ), same data as holotype . Diagnosis. Carapace with dorsal surface eroded, uneven; frontal and orbital regions rugose, lateral parts of anterolateral and branchial regions with oblique striae, rugose; mesogastric, urogastric, cardiac and intestinal regions uneven, eroded ( Fig. 8A, B ); postorbital cristae low, margin uneven, outer edge relatively low, not sharp, weakly demarcated ( Fig. 8B ); external orbital tooth distinct, separated from anterolateral margin by V-shaped cleft; epibranchial tooth distinct ( Fig. 8B ); anterolateral margin lined with low granules, appears gently serrated ( Fig. 8B ); posterior margin of epistome with distinct median triangle ( Fig. 8C ); ischium of third maxilliped subrectangular, not elongate, exopod with short flagellum, ca. half width of merus ( Fig. 8E ); outer surface of chela strongly rugose ( Fig. 8G ); male thoracic sternum, notably sternites 3 and 4, relatively broad, surface with pits ( Fig. 8D ); male pleon triangular, relatively broad medially; telson triangular, lateral margins gently concave; somite 6 transversely trapezoidal, much wider than long, lateral margin gently convex ( Fig. 8D, F ); G1 relatively stout ( Figs. 10A, B , 11A ); reaching to just before suture between sternites 5 and 6 in situ ( Fig. 10K ); subterminal segment gradually tapering to distal part, with concavity on distal part of outer margin but not shelf-like; terminal segment sharply bent at almost 90°, subconical, curving outwards and downwards to long, sharp tip, with very low dorsal flap ( Figs. 10A–D , 11A–C ); G2 longer than G1 ( Figs. 10E , 11D ); females not known. Fig. 5. Kukrimon cucphuongensis ( Đăng, 1975 ) , male (22.3 × 19.2 mm) (ZRC 2022.0058), Ninh Binh Province, Vietnam. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, antennules, antennae and epistome; E, ventral view of cephalothorax and pleon; F, sternopleonal cavity showing G1 in situ; G, outer view of chelae; F, pleon. Fig. 6. Colours in life. A–D, Indochinamon lanae , new species , holotype male (39.0 × 30.0 mm) (ZRC 2022.0049), Quang Ninh Province, Vietnam; E–G, I. signum , new species , holotype male (36.9 × 29.3 mm) (ZRC 2022.0051), Quang Ninh Province, Vietnam; H, paratype female (28.4 × 22.6 mm) (ZRC 2022.0052), Quang Ninh Province, Vietnam. Fig. 7. A, small stream, branch of Ba Che River, Don Dat commune, Ba Che Town, Quang Ninh Province, northeastern Vietnam, type locality of Indochinamon lanae , new species ; B, waterfall at Don Dat commune, Ba Che Town, Quang Ninh Province, northeastern Vietnam type locality of I . signum , new species . Variation. The small paratype female specimen agrees very well with the holotype male in all non-sexual characters. The flagellum on the exopod of the third maxilliped, however, is longer, being as long as the width of the merus. Colour. Dorsal surface of carapace dark brownish green, tips of chelae bright orange, ventral surface dirty beige with scattered brown spots ( Fig. 6A–D ). Etymology . The species is named after Bui Thi Lan, chairwoman of the An Viet Phat group (AVP), who supported the second author for his environmental studies in the province where the taxon was collected. Remarks. Indochinamon lanae , new species , is unusual among congeners in that the epigastric and postorbital cristae in adults is relatively low and not sharp ( Fig. 8A–C ), the male pleon is proportionately wider (especially across somites 3–5) ( Fig. 8D, F ), and the G1 terminal segment is prominently bent at almost right angles ( Figs. 10A–D , 11A–C ). In the strongly bent G1 structure, I . lanae is most similar to I . dangi Naruse, Nguyen & Yeo, 2011 , from Muong Phang district, Dien Bien Province in northwestern Vietnam . In I . lanae , however, the G1 terminal segment is proportionately longer, gently curved and gradually tapering to the tip ( Figs. 10A–D , 11A–C ) (versus proportionately shorter, subtruncate in form and almost straight in I . dangi ; Naruse et al., 2011 : fig. 9d, e). In addition, the epigastric and postorbital cristae of I . lanae are lower and subparallel to the frontal margin ( Fig. 8A, B ) (versus cristae sharp and sloping posteriorly from the frontal margin in I . dangi ; Naruse et al., 2011 : fig. 10a); and the male pleon, especially somite 6, is distinctly wider, with the telson more evenly triangular in shape and the lateral margins gently concave ( Fig. 8D, F ) (versus male pleon less wide with the telson acutely triangular and the lateral margins deeply concave in I . dangi ; Naruse et al., 2011: 10 b). The strongly bent G1 also allies I . lanae with I . flexum ( Dai, Song, Li & Liang, 1980 ) described from Napo County in Guangxi southern China , next to the Vietnam border. This location, however, is some 400 km northwest of the type locality of I . lanae in Quang Ninh Province . Indochinamon lanae can be separated by the epigastric and postorbital cristae being relatively low, rugose and not sharp ( Fig. 8A, B ) (versus epigastric and postorbital cristae sharp in I . flexum ; Dai, 1999 : pl. 11 fig. 8); the third maxilliped exopod possessing only a relatively short flagellum ( Fig. 8E ) (versus flagellum longer, being as wide as the merus in I . flexum ; Dai et al., 1980 : fig. 1.1); the lateral margin of the male telson is gently concave ( Fig. 8F ) (versus lateral margins deeply concave in I . flexum ; Fig. 12C ; Dai et al., 1980 : fig. 1.5); the G1 terminal segment is longer, with the distal part more prominently produced ( Fig. 11A–C ) (versus terminal segment proportionately shorter in I . flexum ; Fig. 12E–H ; Dai et al., 1980 : fig. 1.3); the distal part of the outer margin of the subterminal segment has a concave depression ( Fig. 11A, B ) (versus smooth with only a slight concavity in I . flexum ; Fig. 12E–H ; Dai et al., 1980 : fig. 1.3); and the G2 distal segment is proportionately shorter ( Fig. 11D ) (versus distinctly longer in I . flexum ; Dai et al., 1980 : fig. 1.4). Fig. 8. Indochinamon lanae , new species , holotype male (39.0 × 30.0 mm) (ZRC 2022.0049), Quang Ninh Province, Vietnam. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, ventral view of cephalothorax and pleon; E, left third maxilliped; F, male pleon (telson damaged); G, outer view of chelae. Fig. 9. Indochinamon signum , new species , holotype male (36.9 × 29.3 mm) (ZRC 2022.0051), Quang Ninh Province, Vietnam. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, male pleon; F, ventral view of cephalothorax and pleon; G, chelae. Another unusual feature of I . lanae is that the flagellum on the exopod of the third maxilliped of the adult is relatively short, being barely half the width of the merus ( Fig. 8E ). This is a character shared with Chinese and Vietnamese taxa like I . jingpingense ( Dai, 1995 ) , I . mieni ( Đăng, 1967 ) , I . villosum ( Yeo & Ng, 1998 ) , and I . ou ( Yeo & Ng, 1998 ) (cf. Yeo & Ng, 1998 : figs. 3A, H, 5A, H). In the Laotian I . guttus Yeo & Ng, 1998 , the flagellum is usually long (as long as the width of the merus) but is sometimes almost vestigial ( Yeo & Ng, 1998 : fig. 4H–J). Ecology. This is a fully aquatic species and occurs under larger rock outcrops along small streams in a planted forest of Acacia trees by the side of the Ba Che River ( Fig. 7A ).