Nanosesarma gomantaka Trivedi & Padate & Ng 2024, n. sp.
Creators: name: Trivedi, Jigneshkumar N.
name: Padate, Vinay P.
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Nanosesarma
Nanosesarma gomantaka

description: Nanosesarma gomantaka n. sp.
(Figs. 1–5)
Type material. Holotype, male (CL 5.1 mm, CW 4.7 mm) (LFSC.ZRC-206), Chapora Estuary (15°39’32”N; 73°47’31”E), Goa State, India, coll. M. Bhat, 27 May 2016. Paratypes: 9 males (CL 4.4–5.4 mm, CW 4.1–5.0 mm), 8 females (CL 4.4–5.4 mm, CW 4.1–5.1 mm) (LFSC.ZRC-207), same data as holotype.
Comparative material. Nanosesarma pontianacense (De Man, 1895). 1 male (CL 5.1 mm, CW 4.7 mm); 1 female (CL 4.6 mm, CW 4.9 mm) (LFSC.ZRC-208), 8 males, 10 females [3 ovigerous] (ZRC 2018.0709), on floating ropes and algae, mangroves, Forest-in-a-City Project Ban Laem Pho-Pho Sai, Phum Riang Subdistrict, Chaiya District, Surat Thani Province, Thailand; 9˚22’37.41”N 99˚16’24.56”E, lower areas, coll. P.K.L. Ng, 10 July 2018; 1 male (ZRC 2019.1106), Tai O, western Lantau Island, Hong Kong, coll. L.M. Tsang, 24 September 2019; 1 male, 3 females (ZRC 2019.1717), among oyster clumps, site muddy, Tung Chung, Hong Kong, coll. K. Wong, 13 March 2014; 1 ovigerous female (ZRC 2001.2281), Pandan mangrove, southern Singapore, coll. B.C. Jayne, April 2001; 2 females [broken, poor condition] (ZRC 2011.0584), canal in East Coast, near Victoria Junior College, eastern Singapore, coll. Y.S. Oei, 2 June 2002; 1 male, 1 female (ZRC 1999.1166), Lim Chu Kang mangroves, northern Singapore, coll. P.K.L. Ng & L.W.H. Tan, 21 Octiober 1987; 1 male (ZRC 2012.0299), Sarimbun mangrove, northwestern Singapore, coll. B.Y. Lee et al., 24 February 2011; 1 ovigerous female (ZRC 2012.0239), Kranji mangrove, northern Singapore, coll. B.Y. Lee et al., 16 November 2011; 2 males, 4 females [3 ovigerous] (ZRC 2012.0300), small patch mangrove, Tuas, western Singapore, coll. B.Y. Lee et al., 27 September 2011.
Description. Carapace longer than wide; dorsal surface thickly setose with conspicuous rugosities demarcating regions; lateral margins almost parallel, curving gently along posterolateral margin to posterior carapace margin (Figs. 1a, c; 2a). External orbital angle followed by rudimentary epibranchial tooth, tip of external orbital angle not extending beyond tip of rudimentary epibranchial tooth. Frontal margin wide, obliquely directed, distinctly bilobed, clearly in advance of level of orbits, frontal lobes separated by deep V-shaped depression (Figs. 1a, c; 2a). Antennular fossae transversely ovate. Antennules with 7 articles, folding transversely, tip flagellate. Antennae long, cylindrical, flagellum located in orbital hiatus, extends beyond ocular peduncle (Fig. 6a). Orbits rounded, supraorbital margin weakly granular, inner supraorbital angle continuous with frontal margin; infraorbital margin notched under external orbital angle, followed by granular ridge extending below basal antennal segment. Ocular peduncle short, stout, slightly setose, cornea terminal (Fig. 2a). Buccal cavern wider than long, wider posteriorly; epistome wide, concave, sparsely setose, posterior margin with triangular median lobe and 2 convex lateral lobes, endostomial ridges well-developed. Pterygostomian region covered with reticulate pattern of setae. Third maxillipeds with distinct rhomboidal gap exposing the inner mouth parts when closed; ischium slightly longer than wide, with oblique setose ridge; ischium slightly longer than merus; merus almost as wide as long, with oblique setose ridge; palp slightly shorter than merus, inserted anteroexternally on merus; exopod slender, flattened, with long flagellum (Fig. 3d).
Male chelipeds subequal, stout, almost as long as carapace (Fig. 1a, b). Female chelipeds subequal, smaller than male, almost as long as or shorter than carapace (Fig. 1c, d). Merus with setose granular striations on dorsal surface. Anterior (inner) surface of merus with 3 minute denticles on lower margin. Carpus with setose granular striations on dorsal surface. Palm short, stout, dorsal surface granular, thickly setose, pectinate crest absent; outer surface with granules in reticulated pattern and 2 rows of granules roughly parallel to ventral granular ridge originating from pollex extending posteriorly across palm; inner surface with 2 rows of large granules. Fingers (dactylus and pollex) stout, curved, with rounded spatulate tips, gaping when closed; dactylus with smooth median longitudinal ridge and proximal granules on dorsal surface, outer surface with strong proximal spine (Fig. 3b). Occlusal surface of dactylus with 3 large blunt teeth; occlusal surface of pollex with 1 sub-distal tooth, 1 large median tooth, and 2 proximal molariform teeth (Fig. 3a). Female cheliped dactylus short, no proximal spine, dorsal surface without ridges, outer surface with granules in reticulated pattern and 1 row of granules roughly parallel to ventral granular ridge originating from pollex and extending posteriorly across palm (Fig. 3c).
Thoracic sternum wide in both sexes, with smooth, finely pitted ventral surface; male sternites 1 and 2 completely fused, forming broad triangular structure with convex lateral margins; distinct suture present between sternites 3 and 4, lined with granules; sternites 3 and 4 completely fused; sternopleonal cavity extends to suture between sternites 2 and 3, margin of cavity on sternites 3 and 4 cristate, lined with low granules (Figs. 1b, d; 6b).
Male pleon narrow, triangular, with 6 free somites and telson; surface pitted; lateral margins finely granulated, densely setose; telson longer than wide with anterior surface round; somite 6, 0.6 times wider than long (Figs. 1b; 2c). Female pleon wide, rounded, with 6 free somites and telson; telson rounded, wider than long; margins densely setose (Figs. 1d; 2e).
P2–5, compressed, shorter than chelipeds. P2 short, P3 and P4 longest, subequal in length, P5 short. P4–5 merus flattened, slightly wider distally; anterolateral margin terminates in blunt angle followed by blunt subdistal spine; dorsal surface with several short, sinuous striations, setose; posterodistal margin with minute granules; P5 merus posterodistal margin dentate, separated from tooth on posterolateral corner by notch. Ventral surfaces of carpus with median longitudinal granular ridge. P2 carpus and propodus densely setose on anterior surface, P3–P5 carpus and propodus without dense setae. Propodus 2 times longer than dactylus, posterior margins with scattered long bristles. Dactylus smooth, tips chitinous, slightly curved, with 2 pairs of slender subdistal spines (Fig. 5a–d).
G1 relatively straight, slender except for distal chitinous part which is gently bent at obtuse angle (Fig. 4a); distal part densely covered with long stiff setae which obscures spatuliform chitinous part; main shaft with ventral groove (Fig. 4a, b).
Vulva on distal half of thoracic sternite 6, not touching suture with sternite 5, with semicircular operculum on inner side; lateral parts with low rim but no obvious vulvar cover (Fig. 3e).
Geographical distribution. The species is so far known only from its type locality, Chapora Estuary, Goa State, India.
Habitat. This species inhabits mangrove forest habitat where it lives among the aerial roots of mangroves, under decaying wood, and under large dead shells of oysters (Fig. 1e–g).
Etymology. The specific epithet “gomantaka ” is derived from the ancient Sanskrit name of Goa State, India, which is the type locality of the new species. The name is used as a noun in apposition.
Colour. Carapace of live specimens dark brown over anterior half, darker posteriorly. Chelipeds, pereopods and pleon light brown, pereopods with brown transverse bands. Dark brown setae on chelipeds and pereopods (Fig. 1a–d).
Remarks. De Man (1895: 178, pl. 30 fig. 33) described Sesarma (Episesarma) pontianacensis from a single female specimen (CL 8.17 mm, CW 7.75 mm) from “Pontianak, west coast of Borneo”, with the author noting its general resemblance to much larger S. trapezoidea (H. Milne Edwards, 1837) (now in Shinobium Naruse & Ng, 2020). Of the species he placed in the subgenus Episesarma De Man, 1895, S. pontianacensis is most distinct in its carapace being longer than wide, with a setose body and ambulatory legs which resemble some majoid crabs. Unfortunately, the type female specimen is almost certainly lost. The type was collected during the Hugo Storm expedition to Asia, and extant syntypes are in the Rijksmuseum van Natuurlijke Historie in Leiden (now Naturalis Biodiversity Center); with some supposed material in the Munich Museum (Fransen et al. 1997). The last author has checked for the type in these institutions as well as Muséum national d’Histoire naturelle in Paris and Forschungsinstitut Senckenberg where De Man’s material is known to be kept; the type of Sesarma pontianacensis was not found in these locations, with the late Michael Türkay (personal communication) advising that it was probably lost. A neotype for Sesarma pontianacensis should be selected when the revision of the genus is done. Tesch (1917: 190) grouped S. pontianacensis with S. polita De Man, 1888, S. smithi H. Milne Edwards, 1853, S. rotundata Hess, 1865, S. cruciata Bürger, 1893, S. demani Bürger, 1893, S. jacobsoni Ihle, 1912, S. atrorubens Hess, 1865 and S. trapezoidea H. Milne Edwards, 1837, because of the “distance between external orbital angles distinctly less than the length of the carapace in the median line.” These species are now known to be unrelated and are placed in other genera (Serène & Soh 1970; Davie & Ng 2007; Naruse & Ng 2020; Ng et al. 2020). In establishing Nanosesarma, Tweedie (1950) did not treat S. pontianacensis, and it was Serène & Soh (1970: 393) who formally referred the species to the genus. Nanosesarma pontianacense has since been reported from many locations in Southeast and East Asia (Nobili 1903; Tweedie 1940; Dai et al. 1986; Dai & Yang 1991; Ng & Davie 2002).
Serène (1967) described Nanosesarma tweediei on the basis of specimens collected from Malaysia, Singapore and Vietnam; the holotype being a male specimen (CL 5.8 mm; CW 5.0 mm) from Mersing, southern Malaysia. Serène (1967) compared N. tweediei with N. minutum (De Man, 1887) and N. vestitum (Stimpson, 1858) but not with N. pontianacense, and appears to have not considered this species. In his later work (Serène & Soh 1970: 394), he corrected himself when he noted that “ Nanosesarma tweediei SERENE 1967 corresponds to the male of N. pontianacensis and is its synonym. The two species are marine and have the same habitat.” Ng et al. (2008), however, inadvertently left N. tweediei as a valid species of Nanosesarma. We have compared the material on hand and we agree with Serène & Soh’s (1970) decision - there are no major characters distinguishing them.
The specimens of N. pontianacense from Southeast Asia examined in the present study agree well with the descriptions and figures by (De Man 1895; Tweedie 1940; Serène 1967). Nanosesarma gomantaka n. sp. most closely resembles N. pontianacensis but can easily be distinguished in the form of the frontal lobes and strength of the median notch, shape of the carapace, notably the lateral margins, structure of the external orbital angle, as well as proportions of the male pleon (notably that of somite 6) and the G1 (Table 1).
description: Published as part of Trivedi, Jigneshkumar N., Padate, Vinay P. & Ng, Peter K. L., 2024, A new species of the genus Nanosesarma Tweedie, 1950 (Crustacea: Decapoda: Brachyura: Sesarmidae) from India, pp. 289-298 in Zootaxa 5433 (2) on pages 290-296, DOI: 10.11646/zootaxa.5433.2.8, http://zenodo.org/record/10954089