Bellayra vietnamica, Kolevatov & Thinh & Marin, 2025

Kolevatov, Vasily A., Thinh, Nguyen Van & Marin, Ivan N., 2025, A new species of the leucosiid crab genus Bellayra (Decapoda: Brachyura: Leucosiidae) from delta of Đ ồng Nai-Saigon river system, South Vietnam, Zootaxa 5660 (3), pp. 435-443 : 436-441

Bellayra vietnamica sp. nov.

( Figures 1–4)

Material examined. Holotype: male (9.5 mm × 10.5 mm) ( ZMMU Ma-6236), Vietnam, Thành phố Hồ Chí Minh (Ho Chi Minh City), from bottom Soài R ạp ( Nha Be ) River mouth, 10°28'36.2"N 106°45'02.6"E, bottom trawling from local fisherman boat, about 5–7 m depth, coll. Marin I., Kolevatov V. & Tran Van Tien, September 2022 . Paratype: female (9.0 mm × 9.5 mm) ( ZMMU Ma-6237) . Additional material: 2 males (9.5 mm × 10.5 mm, 9.0 mm × 9.5 mm), 1 female (9.0 mm × 9.5 mm) ( VRTC), same data as for the holotype .

GenBank accession numbers. PV341257, PV341258.

Etymology. The species is named after the country of collection, along the coast of Vietnam, where it was discovered. The name is used as a noun in apposition.

Diagnosis. Carapace rhomboidal, slightly broader than long; dorsal surface punctuated, minutely granular; regions relatively defined, elevated, tuberculated ridge along median part, tubercles getting larger in cardiac and intestinal regions; lateral margins finely tuberculate, epibranchial angle obtuse, distinct tubercle on posterolateral margin; posterolateral angle with prominent obtuse tubercle. Chelipeds robust, large, about 2.8 times as long as carapace width, inner surface of the palm with two ridges on lower and middle areas. Male pleon with 3 articulating pieces, somites 2–6 tightly fused but suture between somites 5 and 6 distinctly visible; somite 6 with weak median denticle; telson broadly triangular, longer than broad. G1 about twice twisted, along its length, tip elongated, tubular, apical lobe with long setae.

Description. Based on holotype male. Carapace rhomboidal, 1.1 times broader than long ( Fig. 2A). Dorsal surface convex, globose; minutely granular with scattered punctae extending to ventral surface, regions relatively indistinct; gastric, cardiac, branchial, and intestinal regions elevated, metagastric, urogastric, cardiac regions elevated with small truncate tubercle medially; distinct median ridge starting from protogastric region merging with elevated intestinal region, reaching highest elevation on urogastric region; protogastric region depressed; branchial region with broad tuberculated ridge originating from posterolateral margin, anterior part longitudinal, posterior part oblique; hepatic facet broad, shallow, floor of facet with scattered punctae, upper and lower margins obtusely beaded, not merging anteriorly, posteriorly facet joins anterolateral margin at obtuse angle ( Fig. 2A, B, D, E, G, H). Anterolateral, posterolateral, posterior margins rimmed by obtuse tubercles; epibranchial angle obtuse; posterolateral margin sinuous, slightly convex. Front slightly elevated, weakly concave, with small median protuberance. Posterior margin almost straight, weakly beaded bearing small blunt protuberances on each lateral side.

Third maxilliped covered with numerous punctae; merus almost as long as ischium along inner margin; ischium 1.7 times longer than wide; basis expanded, more than half length of exopod; carpus, propodus and dactylus not visible in external view when reposed, articulating on inner surface of merus, covered with setae, dactylus apex bearing long setae; exopod outer margin convex, much longer than wide, around twice the length of merus, outer and inner margins bearing fringe of setae ( Figs 4B, 5C).

Chelipeds subequal in length, similar in shape, about 2.8 times longer than carapace width; merus with upper and lower margins beaded, inner surface punctate posteriorly, broad ridge running throughout length terminating in tubercle proximally; carpus about quarter length of merus, elevated medially; palm longer than dactylus, upper and lower margins covered with scattered granules, ventral margin granular, inner surface with 2 ridges on lower and middle areas, lower-most ridge tuberculated running parallel to lower margin of palm; fingers terminating in sharp tooth; dactylus with outer margin smooth, inner margin with ridge running parallel to upper margin; pollex with outer margin bearing scattered granules, inner margin with ridge running parallel to lower margin; cutting margins of dactylus and pollex with blunt denticles covered with scattered setae ( Figs. 2I, J, 5A, B).

Pereopods 2–5 slender, subcylindrical; total lengths decreasing from first to last pair, glabrous; merus longest as compared to carpus, propodus and dactylus; upper and lower margins of carpus, propodus and dactylus covered with long setae ( Fig. 2A, C).

Thoracic sternum covered with sparse punctae, slightly concave, with thickened margins along bases of ambulatory legs; sutures are visible between thoracic sternites 3–7, almost indistinct between sternites 1–3; margin of sternopleonal cavity reaches to suture between sternites 3 and 4; lateral margins of anterior sternites 1 and 2 covered with distinct tubercles ( Fig. 2C).

Pleon with 3 articulating parts, covered with few punctae, somite 1 narrow, with posterolateral angle tuberculated, median part slightly protruding; somites 2–6 fused, immovable, posterolateral angles with prominent bulge, complete suture between somites 5 and 6 visible, barely noticeable weak tubercle on center of somite 6, telson longer than broad, largely triangular, with rounded apex; lateral margins of somite 6 convex ( Figs 4A, 5D).

G1 long, slender, about twice twisted along the length, tip elongated, pointed, tubular, apical lobe with long setae ( Fig. 5E–H). G2 short, about 6 times shorter G1, with slightly protruding basal process.

Paratype female: Generally similar to male except dorsal surface of carapace relatively more convex than male ( Fig. 3B); outer surface of merus and ischium of third maxilliped with longitudinal row of dense setae medially ( Fig. 4C); pleon strongly domed, highly punctate, covering most of thoracic sternites, somites 3–6 fused, with sutures indistinct for all somites ( Fig. 3C, D); gonopore on inner anterior edge of sternite 5, obliquely directed anterodorsally; small membranous oval process on outer margin of opening.

Live colouration. The carapace and chelipeds are generally salmon-white; the ambulatory legs (pereopods 2–5) are yellowish-white ( Fig. 1A, B).

Distribution. Presently, the species is only known from the type locality in the mouth of the Soài Rạp River, Cần Giờ Mangrove Biosphere Reserve, South Vietnam.

Remarks. Bellayra vietnamica sp. nov. is relatively larger than its congeners, where the largest male (holotype) measures 9.5 mm × 10.5 mm, and the largest female (paratype) measures 9.0 mm × 9.5 mm. Whereas the largest known sizes for the other Bellayra species are: B. sexangula — 7.3 mm × 8.2 mm (male) ( Trivedi et al. 2022b); B. persicum — 7.9 mm × 7.8 mm (holotype male) ( Trivedi et al. 2022b); B. taekoae — 8.3 mm × 8.5 mm (holotype female) ( Takeda 1972) and 7.5 mm × 8.0 mm (male) ( Takeda & Nakasone 1991); B. nishihirai from Japan — 6.8 mm × 7.0 mm (holotype male) and 7.6 mm × 8.0 mm (paratype female) ( Takeda & Nakasone 1991); and B. nishihirai from Indonesia — 5.4 mm × 6.0 mm (male) and 6.6 mm × 7.4 mm (female) ( Rahayu & Ng 2003).

The new species, B. vietnamica sp. nov., can be separated from B. persicum by 1) posterior margin of carapace bearing small blunt protuberances on each lateral side ( Fig. 2A, 3B) (versus well-developed blunt teeth on B. persicum ; Trivedi et al. 2022b: Fig. 4a); 2) the presence of four median truncate tubercles on the carapace dorsal surface ( Fig. 2G) (versus only one tubercle on metagastric region on B. persicum ; Trivedi et al. 2022b: fig. 4A, E); 3) weakly developed median denticle on male pleonal somite 6 ( Fig. 4A) (versus distinct median denticle on B. persicum ; Trivedi et al. 2022b: fig. 4D, 5D); 4) the presence of two ridges on lower and middle areas of inner surface of the palm ( Figs. 2I, 5B) (versus presence of three ridges on B. persicum ; Trivedi et al. 2022b: fig. 5A); 5) lateral margin of the tip of G1 is straight ( Fig. 5E) (versus tip of G1 concave on B. persicum ; Trivedi et al. 2022b: fig. 5F, E); and 6) upper loop of G1 is hidden from pleonal view ( Fig. 5H) (versus upper loop of ejaculatory duct is visible from pleonal view on B. persicum ; Trivedi et al. 2022b: fig. 5F, E).

When compared to B. sexangula , the new species, B. vietnamica sp. nov., can be separated by 1) the presence of four median truncate tubercles on the carapace dorsal surface ( Fig. 2G) (versus five visible truncate tubercles on the carapace dorsal surface on B. sexangula ; Trivedi et al. 2022b: fig. 1A, 2A); 2) the presence of two ridges on lower and middle areas of inner surface of the palm ( Figs 2I, 5B) (versus presences of three ridges on B. sexangula ; Trivedi et al. 2022b: figs. 1C, 2C, 3B); and 3) G1 twisted with elongated tip ( Fig. 5E–H) (versus G1 straight with triangle tip on B. sexangula ; Trivedi et al. 2022b: fig. 3E–H).

Bellayra nishihirai can be distinguished from B. vietnamica sp. nov. by 1) clearly rhomboidal carapace ( Fig. 2A, 3B) (versus carapace slightly octagonal on B. nishihirai ; Takeda & Nakasone 1991: fig. 2A, B); 2) only four median truncate tubercles in a row on the carapace dorsal surface ( Fig. 2A, 3B) (versus numerous tubercles on B. nishihirai ; Takeda & Nakasone 1991: fig. 2A, B); 3) adult male chelipeds more than 2.5 times longer than carapace width ( Fig. 2A, 3B) (versus less than 1.8 times on B. nishihirai ; Takeda & Nakasone 1991: fig. 2D); and 3) G1 twisted, with elongated tip ( Fig. 5E–H) (versus straight, with twisted tip on B. nishihirai ; Takeda & Nakasone 1991: fig. 2F, G).

Bellayra taekoae is easily separated from B. vietnamica sp. nov. by 1) a clearly rhomboidal carapace ( Fig. 2A, 3B) (versus carapace slightly octagonal on B. taekoae ; Takeda 1972: fig. 1A; Takeda & Nakasone 1991: fig. 1D); 2) the presence of a single tuberculated ridge on branchial region of carapace ( Fig. 2A, 3B) (versus absent on B. taekoae ; Takeda 1972: fig. 1A; Takeda & Nakasone 1991: fig. 1D); 3) only four median truncate tubercles in a row on the carapace dorsal surface ( Fig. 2A, 3B) (versus numerous tubercles on B. taekoae ; Takeda 1972: fig. 1A; Takeda & Nakasone 1991: fig. 1D); 4) adult male chelipeds more than 2.5 times longer than carapace width ( Fig. 2A, 3B) (versus less than 1.8 times on B. taekoae ; Takeda & Nakasone 1991: fig 1G); and 5) the outer margin of merus of third maxilliped is convex along the entire length ( Fig. 5C) (versus more or less convex outwards at the anterior one third and weakly concave throughout the posterior part on B. taekoae ; Takeda 1972; Takeda & Nakasone 1991: fig. 1G).