Indochinamon signum, Ng & Tri, 2023

Ng, Peter K. L. & Tri, Ngo Van, 2023, A new genus and three new species of freshwater crab (Crustacea: Brachyura: Potamidae) from central and northern Vietnam, Raffles Bulletin of Zoology 71, pp. 70-86 : 82-85

publication ID	https://doi.org/ 10.26107/RBZ-2023-0005
publication LSID	lsid:zoobank.org:pub:BA361B52-E36A-4C15-AB6B-FECA9CEF58AF
persistent identifier	https://treatment.plazi.org/id/587EC3CC-266A-4C56-AD02-0AD3FA78CCF0
taxon LSID	lsid:zoobank.org:act:587EC3CC-266A-4C56-AD02-0AD3FA78CCF0
treatment provided by	Felipe
scientific name	Indochinamon signum
status	sp. nov.

Treatment

Indochinamon signum View in CoL , new species

( Figs. 6E–H View Fig , 9 View Fig , 10F–J, L View Fig , 11E–H View Fig )

Material examined. Holotype: male (36.9 × 29.3 mm) ( ZRC 2022.0051 View Materials ), Don Dat commune, Ba Che Town, Quang Ninh Province, northeastern Vietnam, coll. local people through V. T. Ngo, 14 March 2011 . Paratypes: male (31.0 × 25.4 mm), 1 subadult female (28.4 × 22.6 mm) ( ZRC 2022.0052 View Materials ), same data as holotype .

Diagnosis. Carapace with dorsal surface rugose; frontal and orbital regions gently rugose, lateral parts of anterolateral and branchial regions with strong oblique striae and granules; mesogastric, urogastric, cardiac and intestinal regions with weakly rugose ( Fig. 9B View Fig ); postorbital cristae distinct, sharp, outer edge relatively low, not well marked ( Fig. 9B View Fig ); external orbital tooth distinct, separated from anterolateral margin by distinct V-shaped cleft; epibranchial tooth distinct ( Fig. 9B View Fig ); anterolateral margin lined with sharp granules, appears gently serrated ( Fig. 9B View Fig ); posterior margin of epistome with distinct median triangle ( Fig. 9C View Fig ); ischium of third maxilliped subrectangular, not elongate, exopod with long flagellum, longer than width of merus ( Fig. 9D View Fig ); outer surface of chela with prominent rounded granules and tubercles ( Fig. 9G View Fig ); male thoracic sternum, notably sternites 3 and 4, relatively broad, smooth ( Fig. 9F View Fig ); male pleon triangular, elongate; telson triangular, lateral margins concave; somite 6 transversely rectangular, lateral margin gently convex ( Fig. 9E, F View Fig ); G1 relatively slender ( Figs. 10F, G View Fig , 11E View Fig ); reaching beyond suture between sternites 5 and 6 in situ, to just before tubercles of pleonal locking mechanism on sternite 5 ( Fig. 10L View Fig ); subterminal segment gradually tapering to distal part, distal quarter slender, without obvious shelf on outer margin; terminal segment subconical, gradually tapering to rounded tip, slightly curving outwards, with very low dorsal flap ( Figs. 10F–I View Fig , 11E–G View Fig ); G2 slightly longer than G1 ( Figs. 10J View Fig , 11H View Fig ); vulva relatively large, obliquely ovate, occupying anterior half of sternite 6, margin on suture between sternites 5 and 6 ( Fig. 12B View Fig ).

Variation. There are no major differences between the paratypes and holotype male. The single female specimen is subadult, with the pleon still ovate ( Fig. 12A View Fig ), but its pleopods are already well developed and the vulvae are prominent ( Fig. 12B View Fig ). The tubercles of the pleonal locking mechanism, however, are still visible on the specimen ( Fig. 12B View Fig ).

Colour. Dorsal surface of carapace dark brown, margins of anterolateral margin and orbital margins bright orange; chelipeds and ambulatory legs orangish red, tips of chelae pale yellow; tip of cornea of eyes and centre of merus of third maxilliped bright yellow; ventral surface white and light brown ( Fig. 6E–H View Fig ).

Etymology. The specific epithet is derived from the Latin word for signal, alluding to the distinctive yellow spot present on the tip of the cornea and merus of the third maxilliped (paler in larger specimens).

Remarks. In the features of the carapace and gonopods, I. signum , new species, is most similar to I. phongnha Naruse, Nguyen & Yeo, 2011 , from Phong Nha–Ke Bang National Park, Quang Binh province, in central Vietnam. They also share a similar colour pattern in life, and there are yellow spots on the eyes and merus of the third maxilliped, albeit less prominent ( Naruse et al., 2011: fig. 6a, b). Indochinamon signum , however, differs in having the median triangular structure on the posterior margin of the epistome relatively wider ( Fig. 9C View Fig ) (versus more acutely triangular in I. phongnha ; Naruse et al., 2011: 8 a); the outer surface of the chela is covered with distinct tubercles and granules ( Fig. 9G View Fig ) (versus strongly rugose in I. phongnha ; Naruse et al., 2011: fig. 8b); the male telson is more evenly triangular with the lateral margins gently concave ( Fig. 9E View Fig ) (versus acutely triangular with more concave lateral margins in I. phongnha ; Naruse et al., 2011: fig. 7b); and the G1 subterminal segment is gently converging towards the terminal segment with the terminal segment proportionately longer ( Figs. 10F–I View Fig , 11E–G View Fig ) (versus outer margin of subterminal segment with angled shelf in I. phongnha ; Naruse et al., 2011: fig. 9a, b).

Indochinamon signum is also close to I. tannanti ( Rathbun, 1904) s. str. (sensu Yeo & Ng, 1998) (type locality Lao Koi in Yunnan, China) but the carapace of I. signum , especially the branchial surfaces of the antero- and posterolateral regions are more rugose and granulated ( Fig. 9A, B View Fig ) (versus smoother in I. tannanti ; Yeo & Ng, 1998: fig. 1A, B); the third maxilliped ischium is relatively shorter ( Fig. 9D View Fig ) (versus longer in I. tannanti ; Yeo & Ng, 1998: fig. 2A); and the male telson is evenly triangular in shape ( Fig. 9E, F View Fig ) (versus acutely triangular with more concave lateral margins in I. tannanti ; Yeo & Ng, 1998: fig. 1C). Their G1 structures are similar but the terminal segment of I. signum is proportionately longer ( Figs. 10F–I View Fig , 11E–G View Fig ) (versus shorter in I. tannanti ; Yeo & Ng, 1998: fig. 2B, C, E, F).

Đăng & Hồ (2012: 231) reported “ I. tannanti ” from Hoa Binh province, just west of Hanoi in Vietnam, and while the G1 is superficially similar in structure to that species, it appears to be more like I. signum ( Figs. 10F–I View Fig , 11E–G View Fig ). The carapace features and proportions of the G1 ( Đăng & Hồ, 2012: fig. 84A, B) are very similar to that described here for I. signum . Indochinamon orleansi ( Rathbun, 1904) was described from the Song Da basin far west of Hanoi but this species differs markedly from Đăng & Hồ’s (2012) “ I. tannanti ” in having the anterolateral surface much smoother ( Yeo & Ng, 1998: fig. 6B) and the G1 terminal segment proportionately shorter ( Yeo & Ng, 1998: fig. 2I, J–L).

Indochinamon signum is also superficially similar to I. cua ( Yeo & Ng, 1998) (type locality northwest of Hanoi, Vietnam), but in the new species, the G1 subterminal segment is gently converging towards the terminal segment ( Figs. 10F–I View Fig , 11E–G View Fig ) (versus outer margin of subterminal segment with angled shelf in I. cua ; Yeo & Ng, 1998: fig. 4B, C, E, G); and the third maxilliped ischium is relatively shorter ( Fig. 9D View Fig ) (versus longer in I. cua ; Yeo & Ng, 1998: fig. 4A).

Ecology. This is a fully aquatic species inhabiting higher elevation streams with rocky substrates near the summit of the mountain ( Fig. 7B View Fig ).