Pseudosesarma glabrum Ng & Rani & Nandan 2017, n. sp.
Creators: name: Ng, Peter K. L.
name: Rani, Varghese
name: Nandan, S. Bijoy
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Pseudosesarma
Pseudosesarma glabrum

description: Pseudosesarma glabrum n. sp.
(Figs. 2–5)
Pseudosesarma edwardsii — Shet et al. 2016: 8, 12, fig. 2 (not Sesarma edwardsii De Man, 1887) Material examined. Holotype: male (13.8 × 12.0 mm) (CUSAT 2016-1), mangrove forest (mixed mangrove zone with human settlements), Aroor, Cochin estuary, part of Vembanad wetland, RAMSAR site, Kerala, India, coll. V. Rani et al., 16 January 2016. Paratypes: 1 male (12.2 × 10.3 mm) (CUSAT 2016-2), same data as holotype; 1 male (16.5 × 14.5 mm) (CUSAT 2016-3), same location as holotype, coll. 3 March 2017.
Comparative material. See Ng & Schubart (2017) for material of P. edwardsii (De Man, 1887), and P. crassimanum (De Man, 1887) examined.
Diagnosis. Carapace slightly wider than long, width to length ratio 1.15–1.18 (Fig. 2 A, B); dorsal surface, including anterior part almost glabrous, without dark setae, with only short, barely visible scattered setae on posterolateral regions (Figs. 2 B, 3A); frontal margin wide, each frontal lobe gently convex, median concavity separating lobes wide, shallow (Fig. 2 A, B); postfrontal lobes high, prominent, level with each other (Figs. 2 B, 3A); external orbital tooth short, directed anteriorly, not reaching to level of front, separated from rest of margin by deep, V-shaped cleft (Fig. 2 A, B); lateral margin with 1 distinct low epibranchial tooth, separated from rest of margin by small U-shaped notch (Fig. 2 B); posterolateral margins gently sinuous, subparallel (Fig. 2 A, B). Third maxilliped with longitudinally ovate merus, merus longer than ischium (Fig. 2 C). Chela short, stout, fingers just shorter than palm (measured along ventral margin); outer surface of palm covered with numerous small rounded granules, ventral margin of fixed finger and distal half of palm straight (Fig. 3 B). Groove between male thoracic sternites 3 and 4 distinct, straight (Fig. 3 C). Male pleon broadly triangular, somite 6 wide with distinctly convex lateral margins (Figs. 3 C, 4A). Male sternopleonal cavity with press-button of pleonal locking mechanism on anterior edge of sternite 5. G1 stout, distal part dilated forming bulbous structure, chitinous tip relatively broad, appearing bifurcated (Fig. 4 B–D).
Colour. In life (Fig. 5), the carapace is dark grey with patches of lighter grey. The ambulatory legs are light brown in colour with some parts orange. The merus of the chelipeds is orange with the palm purple and the fingers white.
Etymology. The specific epithet, glabrum, is from the Latin word for smooth and hairless; alluding to smooth dorsal carapace surface of the species which has almost no setae.
Remarks. With regards to the relatively more transversely rectangular carapace and relatively shorter and wider ambulatory meri, P. glabrum n. sp. most closely resembles P. crassimanum, a species known from Myanmar, Thailand, Malaysia, Singapore and Indonesia (Ng & Schubart 2017). Records of this species from Sri Lanka (e.g., Alcock 1900; Ingle & Fernando 1963) actually belong to an undescribed species (see Ng & Schubart 2017). Pseudosesarma glabrum n. sp., however, can easily be separated by the median cleft of the frontal margin being relatively more shallow (Fig. 2 A, B) (deeper in P. crassimanum; cf. Ng & Schubart 2017: figs. 2C, 8); the anterior part of the dorsal surface of the carapace is almost glabrous except for a few very small scattered setae on the posterolateral regions (Figs. 2 B, 3A) (most of surface covered with scattered but distinct stiff setae in P. crassimanum; cf. Ng & Schubart 2017: figs. 2C, D, 8); the ventral margin of the fixed finger and distal half of the palm of the adult chela is almost straight (Fig. 3 B) (distinctly concave in P. crassimanum; cf. Ng & Schubart 2017: figs. 1D, 9); the male pleon is relatively wider (Figs. 3 C, 4A) (relatively narrower in P. crassimanum; cf. Ng & Schubart 2017: fig. 10); and the distal chitinous process is relatively shorter, wider and appears bifurcated (Fig. 4 B–D) (distal chitinous process beak-like, longer and narrower in P. crassimanum; cf. Ng & Schubart 2017: fig. 11B–F, H–L, O–R).
On the basis of geography, the records of “ P. edwardsii ” from the west coast of India (Maharashtra, Karnataka, Goa, Kerala and probably parts of Tamil Nadu) by Kathirasan (2000: 193), Dev Roy & Bhadra (2007: 143, pl. 4 fig. 5), Dev Roy (2008: 131), Dev Roy & Nandi (2008: 497), Dev Roy et al. (2009: 103), Haragi et al. (2010: 10), Pati et al. (2012: 383), Dev Roy (2013: 155) and Shet et al. (2016: 8, 12, fig. 2) may belong to P. glabrum as well. Their material, however, must now be checked to confirm this. The material from other parts of India will certainly need to be re-examined to ascertain if they are really P. edwardsii (sensu Ng & Schubart 2017), P. crassimanum (sensu Ng & Schubart 2017) or otherwise.
Ecology. Pseudosesarma glabrum n. sp. is a semi-terrestrial crab inhabiting the intertidal mixed mangrove zones of Aroor (9°52′1.42′′N, 76°18′54.97′′E), a location on the southern part of the Cochin estuary in Kerala. The habitat is spread over an approximate area of 6–8 hectares, the lower areas being densely covered by old mangrove trees with high litter fall and heavy crab activity. The species is usually abundant during post monsoon period (October–January) in sites with salinities along the mixo-mesohaline range (5±18 ppt). The waters measured 15 ppt when the crabs were collected. Pseudosesarma glabrum n. sp. was observed to occur together with the sesarmids Parasesarma plicatum (Latreille, 1803) and Neosarmatium malabaricum (Henderson, 1893). The species is very active during bright days, usually in the afternoon. It occurs in mixed mangrove vegetation dominated by Avicennia officinalis Linnaeus, and Rhizophora mucronata Lamarck, with more freshwater inflow and low tidal activity. Other mangroves in the area include Acanthus ilicifolius Linnaeus, Bruguiera gymnorrhiza (Linnaeus) Lamarck, Bruguiera cylindrica (Linnaeus) Blume, Kandelia candel (Linnaeus) Druce, Sonneratia caseolaris (Linnaeus) Engler, Rhizophora apiculata Blume, Acrostichum aureum Linnaeus, Excoecaria agallocha Linnaeus, and the rare Bruguiera sexangula (de Loureiro) Poiret. The habitat is muddy to clay-silty, the pH of the sediment generally ranged from 6–7 and the average redox potential from -125 to -250mV. The litter-fall in this area was very high (average 2413.36 ±873.72; cf. Rani et al. 2016)) and is a major source of food for the sesarmid species there. The total carbon of the sediment is very high compared to other sites in Cochin, exceeding 100g / kg. The gut content of the species showed more than 80% mangrove litter, suggesting it has a major role in the crab–litter-fall interaction and carbon cycling in the ecosystem.
description: Published as part of Ng, Peter K. L., Rani, Varghese & Nandan, S. Bijoy, 2017, A new species of Pseudosesarma Serène & Soh, 1970 (Crustacea: Brachyura: Sesarmidae) from Cochin in southwestern India, pp. 263-270 in Zootaxa 4311 (2) on pages 265-269, DOI: 10.11646/zootaxa.4311.2.7, http://zenodo.org/record/847554