Parasesarma bengalense ( Davie, 2003 )

Pati, Sameer Kumar, Rani, Varghese, Sujila, Pallikkara Subrahmanian & Nadan, Sivasankaran Bijoy, 2019, First confirmed record of the sesarmid crab, Parasesarma bengalense (Davie, 2003) (Decapoda: Brachyura) in Indian waters, Nauplius 27, pp. 1-6 : 3-5

Parasesarma bengalense ( Davie, 2003)

( Fig. 2 )

Perisesarma bengalense Davie, 2003: 388 .

Perisesarma bengalensis — Bouillon et al., 2004: 83 (list).

Perisesarma bengalense — Ng et al., 2008: 222 (list); Davie, 2010: 197 (list).

Parasesarma bengalense — Shahdadi and Schubart, 2017: 534 (list and new combination).

Material examined. INDIA: MAHARASHTRA — male (12.20 × 9.94 mm) and female (13.67 × 11.04 mm), Malgund, approximately 2 km north of Ganapatipule , Ratnagiri district (17.164°N, 73.259°E), 9 April 1991, coll. S.V. Mulay ( ZSI-WRC C.1286 ) . KERALA — 2 males (16.10 × 12.94 mm; 11.87 × 9.86 mm) and female (12.52 × 10.52 mm), Thejaswini River, near Palayi Kadavu, Kasaragod district (12.261°N, 75.165°E), 21 October 2018, coll. P.S. Sujila and P.S. Lakshmi (ZSI-WRC C.1910); 2 males (17.13 × 13.99 mm; 11.59 × 9.52 mm), Valiyavattom Island, near Narakkal, Cochin Estuary , Ernakulam district (10.044°N, 76.234°E), 9 March 2019, coll. V. Rani ( ZSI-WRC C.1914 ) .

Diagnosis. Carapace subrectangular, slightly broader than long (cw/cl 1.2–1.5); regions well defined; postfrontal region with 4 prominent, rounded lobes; medial lobes slightly broader than lateral lobes; lateral lobes not separated from inner orbital rim; front deflexed downwards, margin sinuous; anterolateral margin with large, acutely triangular external orbital tooth and smaller, acutely triangular epibranchial tooth, separated from each other by distinct notch; lateral margins subparallel, slightly concave, with numerous short setae; cornea slightly extending beyond tip of external orbital tooth ( Fig. 2A ). Male cheliped with 2 transverse pectinate crests on upper surface of palm; primary pectinate crest with 14–18 tall, broad corneous teeth; secondary pectinate crest shorter than primary pectinate crest, with 13–15 relatively shorter corneous teeth; fingers serrated along cutting margins; fixed finger with strong subdistal tooth along cutting margin; dactylus with strong subdistal tooth and prominent medial tooth along cutting margin, and 16–18 almost symmetrical, distinct tubercles on upper surface; proximal 1–10 dactylar tubercles closely spaced, transversely broadened; distal dactylar tubercles relatively widely spaced, rounded; outer surfaces of palm and proximal portion of dactylus relatively more coarsely granular ( Fig. 2B–E ). Ambulatory legs moderately long, stout ( Fig. 2A ). Male pleon moderately broad; sixth pleonal somite approximately 2.1 times broader than long ( Fig. 2F ). G1 moderately stout, gently curved; apical process corneous, relatively shorter and stouter, bent at angle of about 60° from longitudinal axis ( Fig. 2G ).

Remarks. Parasesarma bengalense mostly resembles P. darwinense (Campbell, 1967) , an endemic species of northwestern Australia, in terms of morphological characters (see Davie, 2003). Parasesarma bengalense is nevertheless distinguished from P. darwinense by the characters of the male cheliped, male sixth pleonal somite, and G1 ( Davie, 2003; 2010).

On the other hand, the molecular data of Shahdadi and Schubart (2017) showed that P.bengalense forms a distinct clade along with P. bidens , P. cricotum (Rahayu and Davie, 2002) , and the more closely related P. guttatum (A. Milne-Edwards, 1869) . Among these, only P. bidens is known to occur in Indian waters with a wider distribution (see Trivedi et al., 2018). The juvenile crabs of P. bengalense are likely to be confused with P. bidens due to similarities in some carapace morphology. For instance, both the species have a prominent epibranchial tooth ( Fig. 2A ; see De Haan, 1837: pl. 16, fig.4), and the male sixth pleonal somite of P.bengalense is almost equally broad as that of P. bidens ( Fig. 2F ; see Davie, 2010; De Haan, 1837: pl. 16, fig.4). The male cheliped of both the species, in particular, has long transverse pectinate crests on the upper surface of the palm and distinct tubercles on the upper surface of the dactylus ( Fig. 2A, B, E ; see Davie, 2010; De Haan, 1837: pl. 16, fig. 4). The dactylar tubercles on the male cheliped, however, are greater in number (16–18), and transversely broadened proximally and rounded distally in P.bengalense ( Fig. 2E ) whereas these tubercles are lesser in number (12 or 13) and oval in P. bidens (cf. Davie, 2010). In addition, both the primary and secondary transverse crests on the palm of the male cheliped are relatively shorter (14–18 and 13–15 teeth, respectively) in P. bengalense ( Fig. 2B ) than in P. bidens (19–22 and 15–20 teeth, respectively) ( Davie, 2010).

Parasesarma bengalense is easily distinguished from the other Indian species of Parasesarma ( P. asperum , P. persicum , P. pictum , and P. plicatum ) mainly by its prominent epibranchial tooth with a distinct notch ( Fig. 2A ) (vs. indistinct epibranchial tooth with an indistinct notch or mostly with a small prominence; see De Haan, 1837: pl. 16, fig. 6; Heller, 1865: pl. 6, fig. 1; Naderloo and Schubart, 2010: fig. 2A; Rahayu and Ng, 2010: fig. 1A; Shahdadi and Schubart, 2017: figs. 1A, C, 2A, C).

Geographical distribution. Parasesarma bengalense is currently known from India (Maharashtra, Kerala and possibly Andhra Pradesh states) (present study; Bouillon et al., 2004), Sri Lanka (Southern and Western provinces) ( Davie, 2003), and Thailand (Ranong and Phuket provinces) ( Davie, 2003; Shahdadi and Schubart, 2017) ( Fig. 1 ) .

Figures

Figure 1. Map showing distribution of Parasesarma bengalense(Davie,2003).1, Malgund (Maharashtra, India); 2, Coringa (Andhra Pradesh, India); 3, Palayi Kadavu (Kerala, India); 4, Valiyavattom (Kerala, India); 5, Ranong (Thailand); 6, Phuket (Thailand); 7, Colombo (Sri Lanka); 8, Galle (Sri Lanka). Circle, present records; diamond, unconfirmed record; square, past records; triangle, type locality.

Figure 2. Parasesarma bengalense (Davie, 2003), male (16.10 × 12.94 mm) (ZSI-WRC C.1910). A, overall dorsal view; B, upper view of transverse crests on palm of right chela; C, frontal view of primary transverse crest on palm of right chela; D, outer view of right cheliped; E, dorsal view of dactylar tubercles on right cheliped; F, male pleonal somites 4–6 and telson; G, leff G1 denuded of setae. Scale bars = 10 mm (A), 4 mm (D), 2 mm (E, F), 1 mm (B, G), 0.5 mm (C).