Abormon, Ng, 2021

Abormon View in CoL gen. nov.

Zoobank: urn:lsid:zoobank.org:pub:C2F054A5-102C-47D3-A08D-949EC8468B37

Type species. Abormon praecalvum sp. nov., by present designation.

Diagnosis. Small adult size (adult CW <15 mm); carapace transversely ovate, low to moderately deep ( CH /CW = 0.4–0.5); dorsal surface gently convex in frontal view, rugose, punctate, sparsely to densely setose; anterolateral margins gently convex, cristate with low granules; posterolateral margins concave medially; front sloping downwards; frontal margin concave medially, broad (FW/CW = 0.35); epigastric cristae very low, visible as 2 broad protuberances; postorbital cristae indiscernible; external orbital angle triangular, with long outer margin, approximately 2.0–2.5 times length of inner margin; epibranchial tooth very low, with very small cleft; cervical grooves barely visible; supraorbital margin gently concave medially; suborbital margin concave, conf luent with supraorbital margin ( Figs. 1A, B View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A, B View Figure 5 , 6A View Figure 6 , 8A, B View Figure 8 , 9A View Figure 9 ). Third maxilliped exopod without flagellum ( Figs. 2B View Figure 2 , 6B View Figure 6 ). Chelipeds sparsely to densely setose; major chela with narrowly or broadly triangular inner distal major tooth on carpus ( Figs. 1A, B View Figure 1 , 2C View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6C View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ). Ambulatory legs sparsely to densely setose, short, relatively stout, longest merus (P3) approximately 0.5 times CW ( Figs. 1A–C View Figure 1 , 4A View Figure 4 , 5A, C View Figure 5 , 6C View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ). Male S2/S3 deep, reaching lateral margins; S3/S4 visible as shallow, broad groove, running from edge of sternopleonal cavity to lateral margins ( Figs. 1C View Figure 1 , 2D View Figure 2 , 5C View Figure 5 , 6D View Figure 6 ). Male sternopleonal cavity long, almost reaching to imaginary line joining anterior part of cheliped coxae ( Figs. 1C View Figure 1 , 2D View Figure 2 , 5C View Figure 5 , 6D View Figure 6 ). Male pleon broad, triangular; pleonal somite 6 trapezoidal, broader than long, distinctly shorter than telson ( Figs. 1C View Figure 1 , 2E View Figure 2 , 5C View Figure 5 , 6E View Figure 6 ). Male telson tongue-shaped, with concave lateral margins ( Figs.1C View Figure 1 , 2E View Figure 2 , 5C View Figure 5 , 6E View Figure 6 ). G1 slender to stout, distinctly sinuous, tip blunt tapering, reaching up to S4/S 5 in situ; flexible zone large; terminal segment curved outwards (at angle approximately 10°–30° from longitudinal axis), stout, conical, long, approximately 0.5–0.6 times combined length of flexible zone and subterminal segment, dorsal flap relatively low, broadly rounded, medially located, not reaching proximal end; subterminal segment gently to distinctly sinuous; groove for G2 median ( Figs. 2D View Figure 2 , 3A–C View Figure 3 , 6D View Figure 6 , 7A–C View Figure 7 ). G2 longer than G1, approximately 1.1–1.2 times G1 length; distal segment relatively long, approximately 0.5 times length of basal segment ( Figs. 3D View Figure 3 , 7D View Figure 7 ). Vulvae on S6, open anteriorly, transversely ovate, relatively small, occupying approximately 0.5 times length of S6, anterior margin touching S5/S6; sternal vulvar cover posterior in position, low or not visible ( Figs. 4C View Figure 4 , 8D View Figure 8 ).

Etymology. The genus name is derived from the Abor Hills, a region of Arunachal Pradesh in the northeast India where the crabs reside, in arbitrary combination with the ending of “ Potamon ”. The gender is neuter.

Comparative material. Pararanguna hemicyclia Naruse, Chia and Zhou, 2018 : paratype male (14.0 × 11.9 mm), Dashan Village   GoogleMaps , Xueshan Town, Fengqing County, Yunnan Province, China (approximately 24.466°N 99.780°E), 1 February 2004, coll. Yang Zheng Bing ( ZRC 2013.0559 View Materials ). Pararanguna semilunata (Dai and Chen, 1985) : holotype male, Xi Yi Village , Baoshan, Yunnan Province, China (approximately 24.928°N 99.323°E), 13 October 1981, coll. A.Y. Dai and G.X. Chen ( IZCAS CB05191 ) GoogleMaps ; paratype female, same data as holotype ( IZCAS CB05191 ) GoogleMaps ; paratype male (21.8 × 17.3 mm), paratype female (20.2 × 16.6 mm), same data as holotype ( ZRC 2020.0085 View Materials ) GoogleMaps . Potamiscus annandali ( Alcock, 1909) : lectotype male (33.0 × 25.0 mm), Nemotha , Cachar District, Assam, India (approximately 25.029°N 92.948°E), collection date unknown, coll. J. Wood-Mason ( ZSIK 6602-3 /9) GoogleMaps . Quadramon aborense ( Kemp, 1913) : syntype male (18.2 × 14.8 mm), road between Rotung and Sireng Stream, East Siang District, Arunachal Pradesh, India (approximately 28.152°N 95.190°E), collection date unknown, coll. S. Kemp ( ZSIK 8011 /10) GoogleMaps .

Remarks. Abormon gen.nov. is clearly a potamiscine, lacking a transverse ridge on S7/S8 ( Figs. 2D View Figure 2 , 6D View Figure 6 ) (cf. Yeo and Ng, 2004). The complete absence of a flagellum on the exopod of the third maxilliped is one of the key characters in Abormon gen. nov. ( Figs. 2B View Figure 2 , 6B View Figure 6 ). Among potamiscine genera that also lack a f lagellum, Abormon gen. nov. is most similar to Pararanguna Dai and Chen, 1985 [with two species: Pa. hemicyclia Naruse, Chia and Zhou, 2018 , and Pa. semilunata (Dai and Chen, 1985) (type species); from Yunnan Province, China (cf. Dai, 1999; Naruse et al., 2018)] due to the relatively small adult size ( CW <22 mm), relatively high carapace with a gently convex dorsal surface ( Figs. 1B View Figure 1 , 5B View Figure 5 , 8B View Figure 8 ; see Naruse et al., 2018: fig. 20B), very low epigastric cristae and indistinct to weakly developed postorbital cristae ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6B View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ; see Dai, 1999: pl. 25, fig.1; Naruse et al., 2018: figs. 19A, 20A), relatively slender G1 with a blunt tip, and stout, relatively long G1 terminal segment with a distinct dorsal f lap ( Figs. 3A–C View Figure 3 , 7A–C View Figure 7 ; see Dai, 1999: fig. 200 (4, 5); Naruse et al., 2018: figs. 19E, 22A, B) (cf. Naruse et al., 2018).

Abormon View in CoL gen. nov. can nevertheless be separated from Pararanguna View in CoL by its sparsely to densely setose dorsal surface of the carapace ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. glabrous dorsal carapace surface; see Dai, 1999: pl. 25, fig. 1; Naruse et al., 2018: figs. 19A, 20A); the medially concave posterolateral margins of the carapace ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. medially almost straight posterolateral margins of the carapace; see Dai, 1999: pl. 25, fig. 1; Naruse et al., 2018: figs. 19A, 20A); the concave lateral margins of the male telson ( Figs. 1C View Figure 1 , 2E View Figure 2 , 5C View Figure 5 , 6E View Figure 6 ) (vs. almost straight lateral margins of the male telson; see Dai, 1999: fig. 200 (2); Naruse et al., 2018: fig. 21); the relatively low dorsal f lap on the G1 terminal segment ( Figs. 3A, B View Figure 3 , 7A, B View Figure 7 ) (vs. relatively high dorsal flap on the G1 terminal segment; see Dai, 1999: fig. 200 (4, 5); Naruse et al., 2018: fig. 22B); and the anteriorly open and transversely ovate vulvae ( Figs. 4C View Figure 4 , 8D View Figure 8 ) (vs. the laterally open and orbicular vulvae; see Dai, 1999: fig. 200 (8); Naruse et al., 2018: fig.23). We have examined the types of both Pararanguna species (see comparative material examined), and the above characters are consistent. Geographically, Abormon View in CoL gen. nov. is also some 600 km apart from the known range of Pararanguna View in CoL in Yunnan.

Abormon View in CoL gen. nov. also has similarities with Potamiscus Alcock, 1909 View in CoL [type species Po. annandali ( Alcock, 1909) ] [currently with 19 species: 11 from Yunnan Province, China; two from Myanmar, and six from northeastern India (see Ng et al., 2020; Pati et al., 2020a)]. Potamiscus View in CoL , however, is clearly polyphyletic (see Shih et al., 2009; Chu et al., 2017; Zhang et al., 2020), with several groups, characterised by different carapaces, ambulatory legs, male pleons, male telsons, male gonopods, and female vulvae (see Ng et al., 2020; Pati et al., 2020a), but all are characterised by the exopod of the third maxilliped possessing at most a short flagellum. Abormon View in CoL gen. nov. can be differentiated from Potamiscus View in CoL s. str. (i.e., based on the type species) by the sparsely to densely setose dorsal surface of the carapace ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. glabrous dorsal surface of the carapace; see Yeo and Ng, 2007: fig. 11A); the medially concave posterolateral margins of the carapace ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. medially almost straight posterolateral margins of the carapace; see Yeo and Ng, 2007: fig. 11A); the very low epigastric cristae and the indiscernible postorbital cristae ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. well-developed epigastric and postorbital cristae, with the latter reaching the epibranchial tooth; see Yeo and Ng, 2007: fig. 11A); the relatively long outer margin of the external orbital angle, approximately 2.0–2.5 times the length of the inner margin ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. relatively short outer margin of the external orbital angle, approximately 1.5 times the length of the inner margin; see Yeo and Ng, 2007: fig. 11A); a very small cleft between the external orbital angle and epibranchial tooth ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. prominent cleft between the external orbital angle and epibranchial tooth; see Yeo and Ng, 2007: fig. 11A); the relatively long male sternopleonal cavity, almost reaching to the imaginary line joining the anterior part of the cheliped coxae ( Figs. 1C View Figure 1 , 2D View Figure 2 , 5C View Figure 5 , 6D View Figure 6 ) (vs. relatively short male sternopleonal cavity, reaching to the imaginary line joining the medial part of the cheliped coxae; see Bott, 1970: pl. 46, fig. 26); the tongue-shaped male telson, with the concave lateral margins ( Figs. 1C View Figure 1 , 2E View Figure 2 , 5C View Figure 5 , 6E View Figure 6 ) (vs. triangular male telson, with almost straight lateral margins; see Bott, 1970: pl. 46, fig. 26); the relatively longer G1 with the tip reaching up to S4/S 5 in situ ( Figs. 2D View Figure 2 , 6D View Figure 6 ) (vs. relatively shorter G1 with the tip reaching slightly beyond S5/S6 up to the proximal third of S 5 in situ; unpublished data); the less strongly curved G1 terminal segment forming an angle of about 10°–30° from the longitudinal axis ( Figs. 3A View Figure 3 , 7A View Figure 7 ) (vs. more strongly curved G1 terminal segment forming an angle of about 50° from the longitudinal axis; see Bott, 1970: pl. 38, fig. 28); the relatively stout and elongated G1 terminal segment (approximately 0.5–0.6 times the combined length of the flexible zone and subterminal segment) ( Figs. 3A–C View Figure 3 , 7A–C View Figure 7 ) (vs. relatively slender and short G1 terminal segment, approximately 0.2 times the combined length of the flexible zone and subterminal segment; see Bott, 1970: pl. 38, fig. 28); the distinct dorsal flap on the G1 terminal segment ( Figs. 3A, B View Figure 3 , 7A, B View Figure 7 ) (vs. absence of the dorsal flap on the G1 terminal segment; see Bott, 1970: pl. 38, fig. 28); and the gently to distinctly sinuous G1 subterminal segment ( Figs. 3A, C View Figure 3 , 7A, C View Figure 7 ) (vs. almost straight G1 subterminal segment; see Bott, 1970: pl. 38, fig. 28).

Some Chinese species of Potamiscus View in CoL s. lat. [ Po. crassus Naruse, Chia and Zhou, 2018 View in CoL , Po. elaphrius Dai, Chen, Liu, Luo, Yi, Liu, Gu and Liu, 1990 View in CoL , Po. fumariatus Naruse, Chia and Zhou, 2018 View in CoL , Po. loshingensis (Wu, 1934) View in CoL , Po. motuoensis Dai, 1990 View in CoL , Po. rongjingensis Dai, Chen, Liu, Luo, Yi, Liu, Gu and Liu, 1990 View in CoL , Po. yongshengensis Dai and Chen, 1985 View in CoL , and Po. yunnanensis (Kemp, 1923) View in CoL ] possess a stout and an elongated G1 terminal segment, and a long G2 distal segment, like those of Abormon View in CoL gen. nov. ( Figs. 3A, D View Figure 3 , 7A, D View Figure 7 ; see also Dai, 1999: figs. 101 (4, 6), 102 (4, 6), 103 (5, 7), 104 (4, 6), 105 (4, 6), 106 (5, 7); Naruse et al., 2018: figs. 19G, H, 30C, E, 33D, E). Abormon View in CoL gen. nov., however, can easily be distinguished from them in possessing indistinct postorbital cristae ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. relatively well-developed postorbital cristae; see Dai, 1999: pl. 12, figs. 4–8, pl. 13, fig. 1; Naruse et al., 2018: figs. 19C, D, 28A, 31A); a relatively broader male pleon ( Figs. 2E View Figure 2 , 6E View Figure 6 ) (vs. relatively narrow male pleon except for Po. fumariatus View in CoL ; see Dai, 1999: figs. 101 (2), 102 (2), 103 (3), 104 (2), 105 (2), 106 (3); Naruse et al., 2018: figs. 29A, 32A); and the presence of a distinct dorsal flap on the G1 terminal segment ( Figs. 3A, B View Figure 3 , 7A, B View Figure 7 ) (vs. no dorsal flap present on the G1 terminal segment except for Po. crassus View in CoL ; see Dai, 1999: figs. 101 (4), 102 (4), 103 (5), 104 (4), 105 (4), 106 (5); Naruse et al.,2018:figs.19G, H, 30C, 33D). In addition, the G1 terminal segment is conical in Abormon View in CoL gen. nov. ( Figs. 3A, B View Figure 3 , 7A, B View Figure 7 ) but cylindrical in Po. elaphrius View in CoL , Po. loshingensis View in CoL , Po. motuoensis View in CoL , and Po. rongjingensis View in CoL (see Dai, 1999: figs. 101 (4), 103 (5), 105 (4), 106 (5); Naruse et al., 2018: fig.19G). Potamiscus fumariatus View in CoL has a relatively broader male pleon ( Figs. 2E View Figure 2 , 6E View Figure 6 ; see Naruse et al., 2018: fig. 29A), but Abormon View in CoL gen. nov. can be separated by its more setose carapace and pereiopods ( Figs. 1A–C View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A–C View Figure 5 , 6A View Figure 6 , 8A, B View Figure 8 , 9A View Figure 9 ) (vs. completely glabrous carapace and pereiopods; see Naruse et al., 2018: fig. 28A); the presence of only a very small cleft between the external orbital angle and epibranchial tooth ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. distinct cleft between the external orbital angle and epibranchial tooth; see Naruse et al., 2018: fig. 28A); and the relatively slender and conical G1 terminal segment with a blunt tapering tip( Figs.3A–C View Figure 3 , 7A–C View Figure 7 ) (vs. relatively stout and columnar G1terminal segment, with a broadly flattened truncate tip; see Naruse et al., 2018: fig. 30A–D). Although both Abormon View in CoL gen. nov. and Po. crassus View in CoL have a distinct dorsal flap on the G1 terminal segment ( Figs. 3A, B View Figure 3 , 7A, B View Figure 7 ; see Naruse et al., 2018: fig. 33C, D), the two species in the new genus have a more setose carapace and pereiopods ( Figs. 1A–C View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A–C View Figure 5 , 6A View Figure 6 , 8A, B View Figure 8 , 9A View Figure 9 ); the cleft between the external orbital angle and epibranchial tooth is very small ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ); the male S3/S4 is relatively more shallow ( Figs. 1C View Figure 1 , 2D View Figure 2 , 5C View Figure 5 , 6D View Figure 6 ); the male telson is relatively broader ( Figs. 1C View Figure 1 , 2E View Figure 2 , 5C View Figure 5 , 6E View Figure 6 ); and the G1 is proportionately more slender ( Figs. 3A, C View Figure 3 , 7A, C View Figure 7 ). In contrast, Po. crassus View in CoL has a completely glabrous carapace and pereiopods (see Naruse et al., 2018: fig. 31A); the external orbital angle and epibranchial tooth are separated by a prominent cleft (see Naruse et al., 2018: fig. 31A); the male S3/ S4 is deeper (see Naruse et al., 2018: fig. 32A); the male telson is relatively narrower (see Naruse et al., 2018: fig. 32A); and the G1 is very stout (see Naruse et al., 2018: fig. 33D).

Two other potamiscine genera also lack a flagellum or only have a short one on the third maxilliped exopod: Quadramon Yeo and Ng, 2007 [with three known species; type Potamon (Potamiscus) aborense Kemp, 1913 ] and Trichopotamon Dai and Chen, 1985 (with three species; type Trichopotamon daliense Dai and Chen, 1985 ). These genera each include one Indian species, Q. aborense ( Kemp, 1913) and T. sikkimense ( Rathbun, 1905) (see Pati and Thackeray, 2018). Abormon gen. nov. is differentiated from Quadramon mainly by the setose dorsal surface of the carapace ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. glabrous dorsal surface of the carapace; see de Man, 1898: pl. 5, fig.9; Kemp, 1913: pl. 18, fig.9; Yeo and Ng, 2007: fig. 10A); the indiscernible postorbital cristae ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. relatively well-developed postorbital cristae; see de Man, 1898: pl. 5, fig. 9; Kemp, 1913: pl. 18, fig. 9; Yeo and Ng, 2007: fig. 10A); the relatively broad external orbital angle ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. relatively acutely triangular external orbital angle; see de Man, 1898: pl. 5, fig. 9; Kemp, 1913: pl. 18, fig. 9; Yeo and Ng, 2007: fig. 10A); and the very small cleft between the external orbital angle and epibranchial tooth ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. distinct cleft between the external orbital angle and epibranchial tooth;see de Man,1898: pl. 5, fig. 9; Kemp, 1913: pl. 18, fig. 9; Yeo and Ng, 2007: fig. 10A). Of the three species of Quadramon , the G1 structure is known only in the type species, Q. aborense ; the two other species [ Q. mooleyitense ( Rathbun, 1904) and Q. obliteratum ( Kemp, 1913) ] are known only from female holotypes. In the G1 structure, Abormon gen. nov. is distinguished from Q. aborense by the blunt tip and the distinct dorsal flap of the terminal segment ( Figs. 3A–C View Figure 3 , 7A–C View Figure 7 ) (vs. G1 terminal segment with an acute tip and lacks a dorsal f lap; see Yeo and Ng, 2007: fig. 10D). Trichopotamon is problematic as the identity and generic position of one of its supposed constituent species, T. sikkimense [described as Potamon (Geothelphusa) sikkimensis Rathbun, 1905 ], is unclear. The species was referred to Potamiscus by Kemp (1913) and Bott (1970), with Ng et al. (2008) including it in Trichopotamon without explanation. The problem with this species is that the holotype is a female deposited in the Muséum national d’Histoire naturelle, Paris (MNHN), and Bott (1970: 159) synonymized it with Po. tumidulus ( Alcock, 1909) without comment. The figure of Po. sikkimensis ( Rathbun, 1905) in Bott (1970: pl. 38, fig. 31, pl. 51, fig. 51) is the lectotype male (ZSIK 5507/10) of Po. tumidulus ( Alcock, 1909) . Bott (1970) had incorrectly synonymised several species under Po. sikkimensis but most were treated as valid species in different genera by Yeo and Ng (2007). Potamiscus sikkimensis s. str. and Po. tumidulus , however, are clearly distinct from each other and actually do not possess the non-sexual diagnostic character states of Potamiscus s. str. (Darren C.J. Yeo, unpublished data). The record of “ Trichopotamon sikkimensis ” from Nepal by Takeda and Sugiyama (2015) will also need to be re-examined to ascertain its identity. In any case, the female holotype of T. sikkimense (MNHN- IU-2014-23050) has a glabrous dorsal surface of the carapace, the relatively well-developed postorbital cristae, an indistinct external orbital angle, and the laterally open vulva, which does not touch S5/S6 (see https://science.mnhn.fr/institution/mnhn/ collection/iu/item/2014-23050), whereas Abormon gen. nov. has a more setose carapace ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ); the postorbital cristae are almost indiscernible ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ); the external orbital angle is distinct ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ); and the anteriorly open vulva touches S5/S6 ( Figs. 4C View Figure 4 , 8D View Figure 8 ). While the male diagnostic features are unknown in T. sikkimense , its indistinct external orbital angle is exceptional among congeners. This casts serious doubt about placing this species in Trichopotamon as well. Abormon gen. nov. can be easily separated from Trichopotamon s. str. (represented by T. daliense and Trichopotamon xiangyunense Naruse, Yeo and Zhou, 2008 ) by the more setose carapace and pereiopods ( Figs. 1A–C View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A–C View Figure 5 , 6A View Figure 6 , 8A, B View Figure 8 , 9A View Figure 9 ) (vs. completely glabrous carapace and pereiopods; see Dai, 1999: pl. 24, fig. 5; Naruse et al., 2008: fig. 13a); the medially concave posterolateral margins of the carapace ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. medially almost straight posterolateral margins of the carapace; see Dai, 1999: pl. 24, fig. 5; Naruse et al., 2008: fig. 13a); the indiscernible postorbital cristae ( Figs.1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. relatively distinct postorbital cristae; see Dai, 1999: pl. 24, fig. 5; Naruse et al., 2008: fig. 13a); a very small cleft between the external orbital angle and epibranchial tooth ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. distinct cleft between the external orbital angle and epibranchial tooth; see Dai, 1999: pl. 24, fig. 5; Naruse et al., 2008: fig. 13a); the barely visible cervical grooves ( Figs. 1A View Figure 1 , 2A View Figure 2 , 4A View Figure 4 , 5A View Figure 5 , 6A View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ) (vs. distinct cervical grooves; see Dai, 1999: pl. 24, fig. 5; Naruse et al., 2008: fig. 13a); the tongue-shaped male telson, with the concave lateral margins ( Figs. 1C View Figure 1 , 2E View Figure 2 , 5C View Figure 5 , 6E View Figure 6 ) (vs. triangular male telson, with almost straight lateral margins; see Dai, 1999: fig. 198 (2); Naruse et al., 2008: fig. 13); and the relatively less stout G1, with a distinct dorsal f lap on the terminal segment ( Figs. 3A–C View Figure 3 , 7A–C View Figure 7 ) (vs. relatively more stout G1, with the terminal segment lacking a dorsal flap; see Dai, 1999: fig. 198 (4, 5); Naruse et al., 2008: fig. 15a, b).

Geographical distribution. Abormon gen. nov. is only known from the Abor Hills in the Upper Siang District of Arunachal Pradesh State, northeastern India.