Tritodynamia bengalensis Trivedi & Mitra & Ng 2021, n. sp.
Creators: name: Trivedi, Jigneshkumar N.
name: Mitra, Santanu
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Macrophthalmidae
Tritodynamia
Tritodynamia bengalensis

description: Tritodynamia bengalensis n. sp.
(Figs. 1–3)
Material examined. Holotype, male (CL 5.0 mm, CW 9.5 mm) (ZSIC 8619 /2), 6 –7 m depth, muddy bottom, off Shankarpur fishing harbor, West Bengal, India, 23 March 2018, from dredge, coll. S. Mitra.
Description. Carapace elliptical, transversely elongate (Figs. 1A, 2A), 1.9 times wider than long; dorsal surface slightly convex longitudinally, glabrous, sparsely punctate. Front slightly directed downwards (Fig. 1C), frontal margin cristate, almost straight, 0.4 times of width between external orbital angles; supraorbital margin cristate with slight notch on inner angle; infraorbital margin present only on outer third, composed of row of small granules; suborbital crista lined with small granules; external orbital angle approximately right-angled, directed anteriorly, ventral surface gently swollen (Figs. 1C). Anterolateral margin cristate, lined with small granules, margin slightly convex behind external orbital angle; posterolateral margin cristate, lined with small granules, converging posteriorly; posterolateral region clearly demarcated from dorsal surface by sinuous line of granules; forming facet-like structure; posterior carapace margin wide, slightly convex (Figs. 1A, 2A). Posterior margin of epistome with broad median triangular structure, lateral margins gently concave (Fig. 2B).
Eye well developed. Antennules typical for the genus. Antennae short with flagellum as long as width of orbit (Fig. 2A). Third maxillipeds narrow, leaving large median opening when closed; ischium slightly shorter than merus, medially concave, inner margin finely toothed, with numerous long setae; outer margin also toothed medially; merus widening distally, with shallow longitudinal grove along inner margin, inner margin finely toothed, with numerous long setae; carpus widening distally, setose; propodus with foliaceous distoextensor lobe, distally rounded with long setae reaching setae of distal margin of dactylus; dactylus attached with proximoflexer angle of propodus, slightly longer than propodus, elongate-elliptical, reaching far beyond foliaceous lobe of propodus, fringed with long setae on margins (Figs. 1B, 2C).
Chelipeds symmetrical, equal in size (Figs. 1A, B); merus with distodorsal margin lined with small granules; carpus rhomboidal, with distodorsal projection, strong external dorsolateral angle having some subconical granules (Fig. 2G); palm with convex outer surface, dorsal surface with row of small granules; 2 grooves on lower margin, both continuing to pollex, both bordered by cristae lined with granules (Fig. 2E), lower most cristae on ventral surface ends in deep concavity on base of pollex (Fig. 2F), upper groove from proximal end of palm, lined with granules throughout; fingers leaving gape when closed; dactylus with 2 median teeth on occlusal margin, distal half with low teeth, pollex with obtuse basal tooth, rest of the margin with low teeth, finger tips corneous, slender, pointed (Fig.1A, 2E).
Ambulatory legs (P2–P5) relatively stout (Figs. 1A, B, 2 A–D), setose; P3 longest, P5 shortest. P2 with merus about 3.2 times as long as wide, with row of granules expanding distally on anterodorsal surface, rows of strong granules posterodorsal and posteroventral margins; dactylus tapering distally, covered with long setae (Fig. 3A). P3 combined length of merus to dactylus about 1.7 times CW; ischium with granules on dorsal surface, posterior margin with strong projecting tooth; merus stout, about 2.5 times as long as wide, anterior and posterior surfaces with numerous rounded, conical granules, posterodorsal and posteroventral margins lined with numerous conical granules; carpus expanding distally, anterior margin smooth, posterodorsal and posteroventral margin with granules, dorsal surface with 3 rows of granules; propodus 3.6 times as long as wide; anterior margin with line of granules; dorsal surface with 2 rows of granules, first row running parallel to anterior margin, second row of granules running parallel to posterior margin, row of long setae present on mid line, posterodorsal margin with row of 18 uneven strong dentiform granules, strong teeth present in proximal half; dactylus tapering distally, covered with long setae (Fig. 2B). P4 fringed with numerous long plumose setae; ischium without projecting teeth on posterior margin; merus stout; 2.5 times as long as wide, anterior, posterior surfaces with numerous rounded or subconical granules, mainly on posterodorsal, posteroventral margins, carpus anterior, posterior margin, dorsal, ventral surface smooth; propodus with convex anterior and posterior margins, 2 times as long as wide, without granules; dactylus slender, tapering distally (Fig. 3C). P5 shortest, most slender, fringed with numerous long plumose setae; merus 3.1 times as long as wide, smooth, carpus smooth, longer than propodus, propodus smooth, shorter than dactylus, dactylus slender, tapering distally (Fig. 3D).
Thoracic sternum broad (Fig. 1B); sternites 1 and 2 completely fused, forming subtriangular structure, medially depressed, appearing sunken; separated from sternite 3 by prominent deeply concave suture. Sternopleonal cavity deep, reaching to just before suture between sternites 2 and 3 (Fig. 2B). Male pleon obtusely triangular with all somites and telson free; somite 6 broadly trapezoidal with lateral margins slightly convex; telson rounded, inserted into distal margin of somite 6 (Fig. 1D). G1 relatively stout, inner margin with long plumose setae, distal part curved with long tapering chitinous process, mostly obscured by dense setae (Fig. 3E, F). G2 small with blunt tip (Fig. 3G).
Distribution. So far known only from the type locality off Shankarpur, West Bengal state, India.
Etymology. The new species is named after the state of West Bengal in India, the type locality of the species.
Ecology. The holotype was collected by fishing vessels using dredge from a depth of 6–7 m, off Shankarpur fishing harbor located in Midnapore district of West Bengal state, India. The bottom substrate was recorded as muddy.
Remarks. Tritodynamia bengalensis n. sp. is most similar to T. bidentata Yang & Tang, 2005 (from Bohai, China), and T. serratipes Anker & Ng, 2014 (from Singapore) in its relatively wide carapace which is about two times as wide as along, possessing a relatively broad P3 merus, and with the P3 length much less than two times the width of the carapace (cf. Yang & Tang 2005; Anker & Ng 2014). Tritodynamia bengalensis n. sp. differs from T. bidentata markedly in having the carapace elliptical in shape (Figs. 1A, 2A) (versus broadly trapezoidal in T. bidentata; cf. Yang & Tang 2005: fig. 1A); the dactylus of the third maxilliped is only slightly longer than the propodus (Fig. 2C) (versus the dactylus of the third maxilliped is prominently longer than the propodus in T. bidentata; cf. Yang & Tang 2005: fig. 1B); the ventral margin of the P3 merus is distinctly serrated with sharp granules (Fig. 3B) (versus ventral margin of the P3 merus more weakly granulated and not appearing serrate; cf. Yang & Tang 2005: fig. 1E); and the G1 distal part possesses a long tapering chitinous process (Fig. 3E, F) (versus distal part divided into two rounded lobes without any elongate chitinous process in T. bidentata; cf. Yang & Tang 2005: fig. 2A). Tritodynamia bengalensis n. sp. appears to be closest to T. serratipes in having a P3 merus which is also prominently serrated along its ventral margin; it can nevertheless be separated by the dactylus of the third maxilliped being relatively shorter, only slightly longer than the propodus (Fig. 2C) (versus the dactylus of the third maxilliped is much longer than the propodus in T. serratipes; cf. Anker & Ng 2014: fig. 1E); there is only one strong and one low tooth at the base of pollex (Fig. 2E) (versus with two strong teeth present in proximal half of pollex in T. serratipes; cf. Anker & Ng 2014: figs. 1F, 3C); the P3 propodus is proportionately longer and is relatively less strongly serrated with small 18 teeth on the ventral margin (Fig. 3B) (versus proportionately shorter and strongly serrated along the ventral margin with 15 large teeth in T. serratipes; cf. Anker & Ng 2014: figs. 1J, K, 3A). Males are not known for T. serratipes.
The G1 structure of T. bengalensis is unusual in that it is relatively slender, is not bilobed distally and possesses an elongate distal process which is sharply bent (Fig. 3E, F). All other species of Tritodynamia have G1s which are distinctly stouter, and the distal part is distinctly bilobed and/or rounded, without any elongate processes (cf. Shen 1932: text-fig. 70b, 72c; Chen 1979: fig.1-10, 1-11; Dai et al. 1980: figs. 10E, 11E; Yang & Sun 1996: fig. 1K; Yang & Tang 2005: fig. 2A; Naruse & Ng 2010: fig. 1f).
description: Published as part of Trivedi, Jigneshkumar N., Mitra, Santanu & Ng, Peter K. L., 2021, Tritodynamia bengalensis n. sp., a new species of brachyuran crab from West Bengal state, India (Decapoda: Brachyura: Macrophthalmidae), pp. 325-330 in Zootaxa 4938 (3) on pages 326-329, DOI: 10.11646/zootaxa.4938.3.3, http://zenodo.org/record/4569679