Parasesarma eumolpe (De Man, 1895 )

Shahdadi, Adnan, Ng, Peter K. L. & Schubart, Christoph D., 2018, Morphological and phylogenetic evidence for a new species of Parasesarma De Man, 1895 (Crustacea: Decapoda: Brachyura: Sesarmidae) from the Malay Peninsula, previously referred to as Parasesarma indiarum (Tweedie, 1940), Raffles Bulletin of Zoology 66, pp. 739-762 : 747-750

Parasesarma eumolpe (De Man, 1895)

( Figs. 2C, D , 3C , 4–6 )

Sesarma (Perisesarma) eumolpe De Man, 1895: 208 , fig. 38.

Sesarma (Chiromantes) eumolpe: Tesch, 1917: 150 ; Tweedie, 1936: 66; Campbell, 1967: 5 (in key).

Sesarma eumolpe: Tweedie, 1950: 340 ; 1954.

Chiromantes eumolpe: Tan & Ng, 1994: 82 (in list); Ng & Sivasothi, 1999: 66–67.

Perisesarma eumolpe: Ng et al., 2008: 222 (in list); Boon et al., 2008, 2009; Davie, 2010: 204 (in key); Chen et al., 2014; Shahdadi & Schubart, 2015: 1083 (table).

Parasesarma eumolpe: Shahdadi & Schubart, 2017: 535 .

Material examined. Neotype (here designated): 1 male (17.4 × 14.7 mm) ( ZRC 2018.0249), coastal mangrove forest, vegetation composed of Bruguiera cylindra, Exoecaria agallocha, Acanthus illifolius , and Acrostichum aureum , very dry forest, clayey mangrove, estuary dammed for irrigation, extensive mudflats, south of Balik Pulau Forest Reserve, Penang, Peninsular Malaysia, coll. K.L. Yeo, 26 April 2000. Other material: 2 males (larger 20.7 × 17.7 mm), 1 female (22.1 × 18.3 mm), 1 juvenile female ( ZRC 2000.1425), same data as neotype; 3 males (largest 13.3 × 11.4 mm), 3 ovigerous females (10.6 × 8.8 mm, 11.8 × 9.6 mm, 19.9 × 15.8 mm), 1 female ( ZRC 2000.1429), coastal mangrove forest, vegetation composed of Bruguiera cylindra, Exoecaria agallocha, Acanthus illifolius , and Acrostichum aureum , very dry forest, clayey mangrove, estuary dammed for irrigation, extensive mudflats, south of Balik Pulau Forest Reserve, Penang, Peninsular Malaysia, coll. N. Sivasothi, 26 April 2000; 1 male (13.1 × 11.2 mm) ( ZRC 2017.1248), Penang, Peninsular Malaysia, coll. Shuhaidi, April 2017. Additional specimens from other parts of its distribution range were also examined (see Table 1).

Distribution. Penang, Peninsular Malaysia (De Man, 1895); Java, Indonesia ( Tesch, 1917); Singapore and neighboring islands ( Tweedie, 1936); Labuan, Borneo, East Malaysia ( Tweedie, 1950); Phuket and Koh Chang, Thailand; Hainan, China; Brunei (present study).

Diagnosis. Medium-size species (up to 28 mm carapace width); carapace subrectangular, slightly broader than long. Front moderately deflexed, with broad, relatively deep, median concavity, postfrontal lobes prominent, median lobes broader than lateral ones, separated by median furrow; dorsal carapace regions clearly indicated, anterolateral margin with sharp exorbital angle and well-developed epibranchial tooth. Chelipeds homochelous; large in adult males, upper surface of palm with 2 transverse pectinated crests, dorsal surface of dactylus with 19–26 low, distinct, transversely broad tubercles with transverse sulcus. Ambulatory legs relatively short, broad. Male pleon triangular with telson slightly longer than basal width. G1 relatively long, gently sinuous, apical corneous process long, bent at angle of about 60° to longitudinal axis, arched in cross section, aperture subterminal. Female pleon broadly rounded, vulva in anterior edge of sternite 6, with operculum rounded.

Remarks. The species was originally described by De Man (1895), from only one male specimen (ca. 20.5 × 16.6 mm) from Penang, Peninsular Malaysia. As such, the type should be either in RMNH or SMF, the latter which includes the material from Göttingen University. We were only able to find two dried specimens of this species in RMNH that do not correspond to the size of the originally examined specimen or its description, and are clearly not types. The type specimen is also not in the Natural History Museum in London; or the Muséum National d’Histoire Naturelle in Paris where some of De Man’s material is deposited. Therefore, the original type is almost certainly no longer extant. In view of the morphological similarity of the various species discussed in this paper, it is important that the identity of Sesarma (Perisesarma) eumolpe De Man, 1895 , be clear and as such, we here designate a neotype for the species. The neotype specimen selected is a male (17.4 × 14.7 mm) (ZRC 2018.0249) from a coastal mangrove forest in the Balik Pulau Forest Reserve in Penang.

This species is a well-known sesarmid model species ( Boon et al., 2008, 2009; Chen et al., 2014), frequently reported, described in detail, and previously often illustrated (see De Man, 1902: 209–213, fig. 38; Tweedie, 1954: fig. 2; Ng & Sivasothi, 1999: 67; Boon et al., 2009: figs. 1, 2; Shahdadi & Schubart, 2015, fig. 2; Shahdadi et al., 2017: figs. 7, 8). Among species of Parasesarma with a distinct carapace epibranchial tooth, this species has a unique tuberculation pattern on its chelar dactyli and is easily recognisable by having large number of these tubercles (19–26) with a marked sulcus on each tubercle ( Figs. 2C, D , 3C ).

The identity of what is here defined as P. eumolpe will need to be re-examined in view of the molecular tree as it suggests that the species is paraphyletic, consisting of several different haplotypes from other localities outside Penang and therefore this may be a cryptic species group. This matter, however, can only be solved with a larger sample size of P. eumolpe from more parts of Southeast Asia.

Figures

Fig. 2. Comparisons of male chelar dactylus and tuberculation patterns, outer views. A, Parasesarma peninsulare new species, holotype male (25.5 × 22.2 mm) (ZRC 2017.1075); B, P. indiarum, paralectotype male (22.8 × 19.4 mm) (RMNH. CRUS. D.19); C, P. eumolpe, neotype male (17.4 × 14.7 mm) (ZRC 2018.0249); D, P. eumolpe, male (24.3 × 20.7 mm) (SMF 49922); E, P. foresti, paratype male (16.6 × 14.4 mm) (ZRC 2003.0481); F, P. messa, paratype male (18.6 × 16.0 mm) (QM-W2452).

Fig. 3. Comparisons of male chelar dactylus and tuberculation patterns, dorsal views. A, Parasesarma peninsulare new species, holotype male (25.5 × 22.2 mm) (ZRC 2017.1075); B, P. indiarum, paralectotype male (22.8 × 19.4 mm) (RMNH. CRUS. D.19); C, P. eumolpe, male (24.3 × 20.7 mm) (SMF 49922); D, P. foresti, paratype male (16.6 × 14.4 mm) (ZRC 2003.0481); E, P. messa, paratype male (18.6 × 16.0 mm) (QM-W2452).

Fig. 4. Parasesarma eumolpe, neotype male (17.4 × 14.7 mm) (ZRC 2018.0249). A, dorsal habitus; B, carapace, dorsal view; C, anterior thoracic sternum and pleon; D, pleon; E, posterior thoracic sternum and pleon.

Fig. 5. Parasesarma eumolpe. A–I, neotype male (17.4 × 14.7 mm) (ZRC 2018.0249); J, female (22.1 × 18.3 mm) (ZRC 2000.1425). A, carapace, front view; B, right chelar pectinated crests; C, right chela, outer view; D, right chela, dorsal view; E, proximal chelae dactylar tubercles; F, left G1, ventral view; G, left G1, dorsal view; H, denuded left G1, apical part, ventral view; I, denuded left G1, apical part, dorsal view; J, vulvae.

Fig. 6. Parasesarma eumolpe, colour in life, male from Mandai, Singapore, specimen not preserved. A, dorsal habitus; B, ventral view; C, frontal view; D, left chela, outer view.