Parasesarma, De Man, 1895

PARASESARMA De Man, 1895 View in CoL

Type species: The Indian Cancer quadratus Fabricius, 1798 , which is a preoccupied name and a synonym of Ocypode plicatum Latreille, 1803 (subsequent designation by Rathbun, 1918; see Ng et al., 2008; Rahayu & Ng, 2010).

Diagnosis: Small- to medium-sized crabs (usually <25 mm cw; largest specimen studied here, cw = 29.4 mm; see Table 1). Carapace rectangular (broader than long; cw/cl ranging from 1.13 to 1.38 in examined material), with carapace regions well defined: front moderately deflexed, with median concavity; four postfrontal lobes with median groove extending to gastric region ( Figs 8A–G, 11A); gastric region well defined; lateral margins of carapace either without tooth, with shallow indentation or with epibranchial tooth of varying size. Eyestalk longer than wide, longer than corneal part in dorsal view; cornea almost as wide as eyestalk ( Figs 8A–G, 9A). Male chelipeds robust; palm with one to three (usually two) oblique (more transverse) pectinated crests on upper surface ( Fig. 5A–E), which consist of tall chitinous teeth, flanked by a large tubercle on inner side ( Fig. 6A–C; except for P. gemmatum , which has a row of fine granules instead of the pectinated crest; see Remarks on this species); chelar dactylus dorsally with a row of tubercles; proximal tubercles at inner side of dorsal face, with virtual line of proximal dactylar tubercles directed towards inner tubercle of pectinated crests ( Fig. 7A). Ambulatory legs dorsoventrally flattened, proportionally short (P4/cw ranges from 1.49 to 1.96; Figs 9B, 11A). Pleon of male relatively short, triangular; somite 3 widest; somite 6 slightly longer than somite 5; telson small, slightly wider than long in most species. Female pleon broad, touching coxae of walking legs; vulvae on anterior part of sternite 6.

Remarks: Members of this genus have experienced several rearrangements and taxonomic changes (e.g. Tesch, 1917; Serène & Soh, 1970; Ng et al., 2008; Shahdadi & Schubart, 2017), and many were originally described under different names (see Table 4). The genus is distributed exclusively in the Indo-West Pacific (for the type localities, see Table 4) and in our revised system now contains 54 nominal species that are listed in Table 4. For a list of synonyms, see Ng et al. (2008) and Shahdadi & Schubart (2017).

The type species of Parasesarma , P. plicatum , has experienced a complicated and unstable taxonomic history until Rahayu & Ng (2010) revised the taxonomy of this species and presumed allied taxa. These authors also recognized P. affine and Parasesarma ungulatum (H. Milne Edwards, 1853) as valid species, which were previously synonymized under P. plicatum by Tesch (1917). Our genetic results also confirmed the separate identities of these species, but did not recognize them as allies.

Shahdadi et al. (2019a) described P. austrawati from northern Australian mangroves and highlighted its phylogenetic position among other related species, focusing on P. lividum from the South Pacific and P. samawati from East Africa. However, P. lividum s.l. has been recorded from different places in Southeast Asia ( Tesch, 1917; Shahdadi et al., 2018a; Li et al., 2019), and the phylogenetic and taxonomic positions of these populations are still unresolved.

Parasesarma bengalense ( Davie, 2003) View in CoL and Parasesarma haswelli ( De Man, 1887) View in CoL were described from the Bay of Bengal, i.e. P. bengalense View in CoL from Sri Lanka ( Davie, 2003) and P. hasswelli from the Mergui Archipelago ( De Man, 1887; Table 4), and both have ~16–19 chelar dactylar tubercles. While describing P. bengalense, Davie (2003) View in CoL did not include P. hasswelli for comparison, but Davie (2010) diagnosed P. hasswelli in his identification key as having asymmetrical chelar dactylar tubercles (vertical distal slope) vs. symmetrical tubercles in P. bengalense View in CoL . We examined the morphology of a series of P. bengalense View in CoL specimens