Indochinamon lanae, 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 : 76-82

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/8F1AF18F-86DC-40DF-8BA4-CA56C6C345F2
taxon LSID	lsid:zoobank.org:act:8F1AF18F-86DC-40DF-8BA4-CA56C6C345F2
treatment provided by	Felipe
scientific name	Indochinamon lanae
status	sp. nov.

Treatment

Indochinamon lanae View in CoL , new species

( Figs. 6A–D View Fig , 8 View Fig , 10A–E, K View Fig , 11A–D View Fig )

Material examined. Holotype: male (39.0 × 30.0 mm) ( ZRC 2022.0049 View Materials ), 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 GoogleMaps . Paratype: juvenile female (16.8 × 13.5 mm) ( ZRC 2022.0050 View Materials ), same data as holotype GoogleMaps .

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 View Fig ); postorbital cristae low, margin uneven, outer edge relatively low, not sharp, weakly demarcated ( Fig. 8B View Fig ); external orbital tooth distinct, separated from anterolateral margin by V-shaped cleft; epibranchial tooth distinct ( Fig. 8B View Fig ); anterolateral margin lined with low granules, appears gently serrated ( Fig. 8B View Fig ); posterior margin of epistome with distinct median triangle ( Fig. 8C View Fig ); ischium of third maxilliped subrectangular, not elongate, exopod with short flagellum, ca. half width of merus ( Fig. 8E View Fig ); outer surface of chela strongly rugose ( Fig. 8G View Fig ); male thoracic sternum, notably sternites 3 and 4, relatively broad, surface with pits ( Fig. 8D View Fig ); 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 View Fig ); G1 relatively stout ( Figs. 10A, B View Fig , 11A View Fig ); reaching to just before suture between sternites 5 and 6 in situ ( Fig. 10K View Fig ); 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 View Fig , 11A–C View Fig ); G2 longer than G1 ( Figs. 10E View Fig , 11D View Fig ); females not known.

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 View Fig ).

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 View Fig ), the male pleon is proportionately wider (especially across somites 3–5) ( Fig. 8D, F View Fig ), and the G1 terminal segment is prominently bent at almost right angles ( Figs. 10A–D View Fig , 11A–C View Fig ).

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 View Fig , 11A–C View Fig ) (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 View Fig ) (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 View Fig ) (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 View Fig ) (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 View Fig ) (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 View Fig ) (versus lateral margins deeply concave in I. flexum ; Fig. 12C View Fig ; Dai et al., 1980: fig. 1.5); the G1 terminal segment is longer, with the distal part more prominently produced ( Fig. 11A–C View Fig ) (versus terminal segment proportionately shorter in I. flexum ; Fig. 12E–H View Fig ; 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 View Fig ) (versus smooth with only a slight concavity in I. flexum ; Fig. 12E–H View Fig ; Dai et al., 1980: fig. 1.3); and the G2 distal segment is proportionately shorter ( Fig. 11D View Fig ) (versus distinctly longer in I. flexum ; Dai et al., 1980: fig. 1.4).

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 View Fig ). 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 View Fig ).