Tiwaripotamon bellum Ng & Tri 2022, n. sp.
Creators: name: Ng, Peter K. L.
name: Tri, Ngo Van
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Potamidae
Tiwaripotamon
Tiwaripotamon bellum

description: Tiwaripotamon bellum n. sp.
(Figs. 1–5)
Type material. Holotype: male (46.7 × 34.2 mm) (ZRC 2022.773), semi-aquatic, karst outcrop on hillside, Ng ọc Sõn commune, Lạc Sõn District, Hoà Bình province, Vietnam, belonging to Lạc Sõn – Ng ổ Luông Natural Reserve, Hòa Bình province, 20°26'6.04"N 105°24'24.91"E, 478 m asl, coll. V. T. Ngo, at night (2000 hours), 16 May 2022. Paratypes: 2 males (41.4 × 31.3 mm, 51.3 × 36.6 mm), 2 females (46.7 × 34.2 mm, 51.2 × 36.9 mm) (ZRC 2022.774), same data as holotype.
Diagnosis. Carapace transversely ovate, surfaces smooth, inflated (Figs. 2A, B, 3A); epigastric cristae very low, marked by low striae; postorbital cristae not visible (Figs. 2A, B, 3A); external orbital tooth triangular, clearly demarcated from anterolateral margin by cleft (Fig. 3A); epibranchial tooth small but visible, rest of anterolateral margin smooth, subcristate (Fig. 3A); posterior margin of epistome relatively short, median lobe broadly triangular, confluent with almost straight lateral margin, separated by fissure (Fig. 3B). Male thoracic sternites prominently punctate (Figs. 2C, 3D, 4A, B). Tubercle of male pleonal locking mechanism on submedian part of somite 5 (Fig. 3C). Ambulatory legs relatively long (Figs. 2A, 3F). G1 relatively slender, subterminal segment gently curved outwards, terminal segment slender, gently curved, tapering to subtruncate tip, with low but distinct dorsal lobe on proximal part (Fig. 5A–D). G2 longer than G1, distal segment two-thirds length of basal segment, tip with sharp fold (Fig. 5E, F). Vulva large, ovate, aperture V-shaped, opening obliquely inwards, occupying distal two-thirds of thoracic sternite 6 (Fig. 4F).
Description of holotype male. Carapace transversely ovate, surfaces smooth, regions not demarcated, cervical grooves not visible; H-shaped gastro-cardiac depression barely discernible (Figs. 2A, B, 3A); dorsal surface (including branchial regions) convex, inflated, including branchial regions (Figs. 2A, B, 3A); epigastric cristae very low, marked by low striae; postorbital cristae not visible (Figs. 2A, B, 3A). Frontal margin almost straight, entire in dorsal view, level with tips of external orbital tooth in dorsal view; median part distinctly deflexed; contiguous with supraorbital margin (Figs. 2A, B, 3A). Supraorbital margin sinuous, without clefts or fissures (Fig. 3A). External orbital tooth triangular, inner and outer margins subequal; clearly demarcated from anterolateral margin by cleft (Fig. 3A); epibranchial tooth low but clearly visible, rest of anterolateral margin distinctly convex, smooth, subcristate; posterolateral margin gently sinuous, converging towards gently sinuous posterior carapace margin (Fig. 3A). Orbits ovate, large; eyes completely filling space; cornea large, peduncle relatively short (Figs. 2A, B, 3A). Antennules longitudinally narrow, folding laterally (Figs. 2B, 3B); antennae short, not extending beyond orbit (Figs. 2B, 3B). Epistome longitudinally narrow; posterior margin relatively short, median lobe broadly triangular, confluent with almost straight lateral margin, separated by fissure (Fig. 3B). Suborbital margin convex, smooth, without inner tooth; suborbital, subhepatic, pterygostomial and sub-branchial regions almost smooth (Fig. 2B).
Third maxillipeds relatively short; merus shorter and narrower than ischium, surface slightly rugose; ischium subquadrate with undiscernible median sulcus; exopod short, curved, reaching to one-third length of merus, with short flagellum shorter than merus width (Figs. 2B, 3E).
Chelipeds elongate; right one prominently larger (Figs. 2A, 3H, I). Basis-ischium with granules on ventral margin; ventral margins of merus lined with tubercles, dorsal margin uneven, distinctly rugose; carpus with sharp spine on inner angle, surface gently rugose; chela covered with scattered small sharp granules, denser on ventral and subventral surfaces; fingers longer than palm; fingers gently curved with larger cutting teeth on proximal half (Figs. 2A–C, 3H, I).
Ambulatory legs relatively long; second leg longest, fourth leg shortest; merus with dorsal margin subcristate, margin uneven but not serrate; carpus with subdorsal ridge; propodus long, with shallow median sulcus; dactylus gently curved (Figs. 2A, 3F).
Thoracic sternites 1 and 2 completely fused, lateral margins strongly convex; separated from sternite 3 by prominent gently sinuous ridge; sternites 3 and 4 fused except for shallow lateral groove that is medially interrupted, surface of sternites prominently punctate (Figs. 2C, 3D). Somite 8 not visible when pleon closed. Sternopleonal cavity reaching to imaginary line connecting median part of coxae of chelipeds, distal part subcristate; tubercle of male pleonal locking mechanism on submedian part of somite 5 (Figs. 2C, 3C, D).
Pleon broadly triangular; somite 1 longitudinally narrow, reaching to edges of coxae of fourth ambulatory legs; somite 2 slightly wider than somite 1; somite 3 widest, subrectangular; somites 4 and 5 trapezoidal; somite 6 wide, rectangular; telson wide, lateral margin gently concave (Figs. 2C, 3D, G).
G1 relatively slender, subterminal segment gently curved outwards, gently tapering distally; terminal segment clearly separated from subterminal segment, slender, gently curved, tapering to subtruncate tip, with low distinct dorsal lobe on proximal part (Figs. 3C, 5A–D). G2 longer than G1, distal segment two-thirds length of basal segment, tip with sharp fold (Fig. 5E, F).
Females. The females agree with the male in all aspects except for their more slender and relatively shorter chelipeds. The pleon is ovate and covers almost the entire surface of the thoracic sternum when closed (Fig. 4E). The vulva is large, ovate, V-shaped, and opens obliquely inwards, occupying the distal two-thirds of sternite 6 (Fig. 4F).
Variation. There is no significant variation in the non-sexual characters. The holotype male has a short flagellum on both exopods of the third maxilliped (Fig. 3E). The smaller male paratype has the same condition but in the largest male has no trace of a flagellum on both third maxillipeds. In the two female paratypes, the left third maxilliped exopod has no flagellum while the right side has a short one. In the males, the pleons vary slightly with size. The largest male has proportionately the widest pleon with the widest telson (Fig. 4B, D). It is less wide in the smaller holotype male (Fig. 3D) and is the narrowest in the smallest male (Fig. 4A, C).
Colour. The dorsal surface of the carapace and ambulatory legs are purplish-black (Fig. 1A, B); the orbital margins being orangish-red (Fig. 1B). The mouthparts, chelipeds and ventral surfaces are orangish-red (Fig. 1A, D). The colours in all the specimens were consistent and did not show variation.
Etymology. The name is derived from the Latin “bella” for beautiful; alluding to the distinctive colour of the species.
Remarks. In the features of the carapace and legs, Tiwaripotamon magum n. sp. is similar to T. vietnamicum; and their type localities are also near each other. Tiwaripotamon vietnamicum was described from Cuc Phuong National Park in Ninh Binh Province; while T. bellum n. sp. was from Lạc Sõn-Ngổ Luông Natual Reserve in Hòa Bình province, about 50 km from this location. Despite their similar carapace morphologies, T. bellum n. sp. can easily be separated in possessing a low but distinct epibranchial tooth (Fig. 3A) (versus absent in T. vietnamicum; Đăng & Hồ 2002: pl. 2, fig. 2A; Đăng & Hồ 2012: fig. 78A; Shih & Do 2014: fig. 6A, C, D); and the ambulatory meri are proportionately shorter (Fig. 3F) than in T. vietnamicum (cf. Shih & Do 2014: fig. 6A–D). Most significantly, their G1 morphology is completely different, with that of T. bellum n. sp. having the terminal segment gently curved, the tip subtruncate and with a low dorsal lobe on the proximal part (Fig. 6A–D) (versus G1 terminal segment filiform with a sharp tip and without any trace of a dorsal lobe in T. vietnamicum; Đăng & Hồ 2002: fig. 2E; Đăng & Hồ 2012: fig. 78D). Their colour in life is also different, with the carapace of T. bellum n. sp. a very dark purplish black (Fig. 1A, B) versus evenly orangish-red throughout in T. vietnamicum (see Shih & Do 2014: fig. 6A–D).
Tiwaripotamon bellum n. sp. is one of the largest known species of the genus to date, with the largest male measuring 51.3 × 36.6 mm and the largest female 51.2 × 36.9 mm (ZRC 2022.774). Do et al. (2016) previously recorded a male of T. pluviosum measuring 39.8 × 28.8 mm from southern China, with a male of T. vietnamicum from Vietnam reaching 44.5 × 32.8 mm. Shih & Do (2014) had a large male of T. vietnamicum measuring 49.6 × 36.7 mm and a female 47.9 × 35.8 mm while the types reached 53.0 mm in carapace width (Đăng & Hồ 2002: 4).
Ecology. This species inhabits crevices or small caves under karst outcrops. They are nocturnal and come out only after heavy rain.
Conservation. This relatively large species is collected for food by local villagers and is also sold in markets for the pet trade. From the surveys conducted, the species occurs in seven karst forest communes in Lạc Sõn and Tân Lạc Districts in Hoa Binh province, covering an area of over 19,000 ha. Although the area it occurs in is partially protected, the collection of the crab for food and commerce means it should at least be regarded as vulnerable (cf. Cumberlidge et al. 2009).
description: Published as part of Ng, Peter K. L. & Tri, Ngo Van, 2022, A new semiterrestrial crab from limestone hills in Vietnam (Crustacea: Brachyura Potamidae: Tiwaripotamon), pp. 578-586 in Zootaxa 5213 (5) on pages 579-585, DOI: 10.11646/zootaxa.5213.5.6, http://zenodo.org/record/7381743