Parasesarma peninsulare, Shahdadi & Ng & Schubart, 2018

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 : 752-760

publication ID	https://doi.org/ 10.5281/zenodo.5363335
publication LSID	lsid:zoobank.org:pub:67DA8444-6F26-4675-AE8C-D12B626DB2AB
persistent identifier	https://treatment.plazi.org/id/35D30468-9AF9-422C-9E50-C3D5C2397342
taxon LSID	lsid:zoobank.org:act:35D30468-9AF9-422C-9E50-C3D5C2397342
treatment provided by	Valdenar
scientific name	Parasesarma peninsulare
status	sp. nov.

Treatment

Parasesarma peninsulare View in CoL new species

( Figs. 2A View Fig , 3A View Fig , 10–14 View Fig View Fig 11 View Fig View Fig 13 View Fig )

Sesarma (Chiromantes) bidens indica: Tweedie, 1936: 66 View in CoL . (not Sesarma bidens var. indica De Man, 1902 View in CoL )

Sesarma bidens indiarum: Tweedie, 1940: 93 View in CoL (part) (not Sesarma bidens indiarum Tweedie, 1940 View in CoL ).

Chiromantes indiarum: Tan & Ng, 1994: 82 (list).

Perisesarma indiarum: Boon et al., 2008 View in CoL ; Huang et al., 2008; Boon et al., 2009; Ng et al., 2008: 225, fig. 162 (not Sesarma bidens indiarum Tweedie, 1940 View in CoL ).

Material examined. Holotype: 1 male (25.5 × 22.2 mm) ( ZRC 2017.1075 View Materials ), Mandai mangroves, Singapore, coll. C.D. Schubart & N. Sivasothi, 25 July 2000 (= S 134 in Table 1) ; Paratypes: 21 specimens, as listed in Table 1.

Comparative material. Parasesarma foresti ( ZRC 2003.0481, paratype male); P. messa (QM, W2446, paratype male) (see Table 1 and Material and Methods section) .

Diagnosis. Medium-size species (up to 26 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 deep median furrow; dorsal carapace regions well indicated, anterolateral margin with sharp exorbital angle and well-developed epibranchial tooth. Chelipeds homochelous; large in males, upper surface of palm with 2 transverse pectinated crests, dorsal surface of dactylus with 10–12 low, distinct, transversely very broad tubercles with distinct transverse sulcus. Ambulatory legs relatively short, broad. Male pleon triangular with telson slightly longer than basal width. G1 relatively long, straight, apical corneous process long, bent at angle of about 54° to longitudinal axis, arched in cross section, aperture subterminal. Female pleon broadly rounded, vulva in anterior edge of sternite 6, with operculum rounded.

Description. Small to medium sized sesarmid (up to 26 mm maximum carapace width, SMF 50745), carapace subrectangular, slightly broader than long, greatest width between exorbital angles (cw/cl 1.17 ± 0.03, N=20). Dorsal carapace surface smooth, shining, punctate, with numerous short, transverse to slightly oblique crests edged with rows of short setae, sometimes forming low tufts. Front 0.58 ± 0.01 times carapace width (N=20), moderately deflexed, with broad, relatively deep, median concavity ( Fig. 10A View Fig ). Postfrontal lobes prominent, median lobes broader than lateral ones, separated by deep furrow ( Fig. 11A, B View Fig 11 ). Dorsal carapace regions clearly indicated; gastric region most distinct; cardiac region separated from intestinal region, lateral branchial ridges prominent, upper orbital border smooth, lower orbital border finely granulate, anterolateral margin with sharp exorbital angle, well-developed epibranchial tooth (carapace width between epibranchial teeth slightly less than width between exorbital angles); no indication of second epibranchial tooth, lateral margin slightly concave, lined with row of short setae. Eyes pigmented, cornea as wide as eyestalk ( Fig. 10A View Fig ).

Chelipeds homochelous ( Figs. 10 View Fig , 11A View Fig 11 ). Chela large ( Figs. 10 View Fig , 11A View Fig 11 , 14A–D View Fig ) (ratio of palm length/carapace width = 0.65 ± 0.13, N=20), adult males have a higher ratio of palm length/carapace width (e.g., 0.70 ± 0.13, N= 13 males) in comparison to females (e.g., 0.55 ± 0.05, N= 7 female); chelae relatively robust ( Fig. 11F View Fig 11 ) (width = 0.53 ± 0.04 × length, N=19, range 0.45–0.60). Merus with granulate dorsal border, distinct subdistal spine, proximal third decorated with long setae; ventral border granulate; anterior border granulate, with distinct subdistal spine; inner face smooth with 2 longitudinal rows of setae, ventral row more prominent, continuous, with longer setae, dorsal row interrupted, setae extending to dorsal border; anterior face also smooth, outer face with transverse lines of fine granules and scattered small chitinous spines. In males, upper surface of palm with 2 transverse pectinate crests ( Fig. 11E View Fig 11 ), distal (primary) crest composed of 13–22 tall, broad teeth (19 on chela of holotype) ( Fig. 11G View Fig 11 ); secondary crest well-developed with 7–17 teeth (11 and 12 on chelae of holotype); both crests terminate at inner end in short swollen, tubercular ridge, with several blunt granules at outer end; in some specimens a row of coarse granules proximal to second crest, scattered fine setae distal to primary crest; upper margin of palm with granules; outer surface of palm without setae, coarsely granular except for smooth, punctate fixed finger, no indication of median longitudinal ridge ( Fig. 11F View Fig 11 ); inner surface of palm coarsely granular except area facing carpus; ventral border of chelae sinuous, with rows of fine granules on proximal half, length of cutting margin of fixed finger 0.41 ± 0.02 times length of entire propodus (N=20). Dactylus 0.60 ± 0.02 times propodus length, gently arched downwards and moderately curved inwards distally ( Figs. 2A View Fig , 3A View Fig , 11E, F View Fig 11 ), dorsal surface with 10–12 low, transversely broadened tubercles, in males all tubercles distinct to tip ( Figs. 2A View Fig , 3A View Fig , 11E, F View Fig 11 ), each tubercle elongated transversely, with transverse distinct keel, followed by a shallow sulcus ( Figs. 3A View Fig , 11H View Fig 11 ), tubercles with fine longitudinal lines; except for 1 or 2 proximal tubercle(s), remaining ones slightly asymmetric, distal slope longer than proximal one; dactylar tubercles in females ( Fig. 13D, E View Fig 13 ) (not clearly differentiated in juvenile males): low, rounded to slightly oval tubercles with or without indistinct keel and sulci; additional row of about 11–17 rounded tubercles on proximal two thirds of inner edge of dorsal surface of dactyli in both sexes. Tips of fingers chitinous, crossing when closed, adult males with a narrow gap when fingers closed; cutting edge of both fingers with a series of variably sized teeth and groups of long setae at inner side ( Fig. 11F View Fig 11 ).

Ambulatory legs ( Fig. 10 View Fig ) relatively short, broad; third pair longest, total length ca. 1.7 times carapace width in holotype, meri with anterior margin crenulated, dorsal faces with transverse lines of fine granules (except for the fourth pair), third pair with merus 2.23 ± 0.17 times as long as wide (N=19), propodus 3.20 ± 0.37 times as long as wide, dactylus 0.73 ± 0.05 times length of propodus (N=17).

Male pleon ( Figs. 10B View Fig , 11C View Fig 11 ) triangular; telson as long as basal width, almost pentagonal, slightly longer than somite 6 (=1.14 ± 0.08 times length of somite 6, N=13); somite 6 longer than others, ca. 2.04 ± 0.13 times wider than long; somites 4 and 5 trapezoidal; somite 3 widest, laterally convex; somite 2 medially longer than lateral edges ( Fig. 11D View Fig 11 ).

G1 ( Fig. 12 View Fig ) relatively long, straight ( Fig. 12A View Fig ); stem triangular, with blunt angles in cross section; apical corneous process long, bent at an angle of about 54° to longitudinal axis ( Fig. 12B View Fig ), arched in cross section, aperture positioned

RAFFLES BULLETIN OF ZOOLOGY 2018

subterminal-dorsally ( Fig. 12C View Fig ). Scattered short setae along most of gonopod, apical end covered by longer setae, almost completely covering corneous tip; two kinds of setae recognisable, long simple setae, and some plumose setae restricted to outer side of subapical part ( Fig. 12D View Fig ).

Female ( Figs. 13 View Fig 13 , 14E–H View Fig ) with proportionately smaller chelipeds; distal dactylar pectinate crest well developed, prominent as in male, but proximal crest reduced to row of granules; dactylar tubercles well-developed, round, distinct to tip ( Fig. 13D, E View Fig 13 ). Pleon broad, rounded, or even laterally slightly ovate, broadest at somite 4, fringed with long setae. In adults, pleon touches coxae of ambulatory legs, telson ca. 1.23 ± 0.09 (N=6) times wider than long, inserted into somite 6 more than half of its length ( Fig. 13B View Fig 13 ). Vulva in depression on anterior edge of sternite 6, touching posterior margin of sternite 5; operculum rounded, positioned anterior to the gonopore ( Fig. 13C View Fig 13 ).

Colour. Carapace dark, partly scattered with blue spots, chelae dark brownish-red externally, except for the distal half of fingers which are bright red, internal side yellow to orange ( Fig. 14 View Fig ) (also see Ng et al., 2008: 225, fig. 162). Facial bands often blue or green (see Huang et al., 2008).

Etymology. This species is named after its known area of distribution, the Malay Peninsula.

Distribution. Based on present material, so far known from both coasts of the Malay Peninsula, including the western coast to Thap Lamu, eastern side Chumphon (both Thailand), southward to Singapore and Batam Island (Riau Archipelago, Indonesia).

Habitat. In its distribution range, P. peninsulare new species is a relatively common species in mangroves swamps and can sometimes be found in good numbers, occasionally in partial sympatry with P. eumolpe , on muddy substrates. They are active burrowers, with burrow mouths often found within the aerial root systems of mangrove tree ( Huang et al., 2008; Boon et al., 2009).

Remarks. As discussed earlier (see Results and Discussion), this species resembles four other phylogenetically related species ( P. foresti , P. eumolpe , P. indiarum , and P. messa ) in its general morphology. The tuberculation pattern in P. eumolpe , however, is markedly different from the new species in having in total 19–26 tubercles, while it is about 10–12 in the new species. It can be difficult to discriminate females and juveniles of P. peninsulare new species from P. foresti , P. indiarum , and P. messa ; and for these species, the vulvae and G1 are not morphologically sufficiently different to separate them with any reliability. All have relatively rounded low chelar dactylar tubercles, but the morphology of these tubercles in adult males easily distinguishes the new species from all others (i.e., the tubercles of the new species are considerably more elongated transversely, with a distinct transverse keel followed by a shallow transverse sulcus, while no indication of such sulci is present in the other three species) ( Figs. 2 View Fig , 3 View Fig ). The genetic data confirms the monophyly of the analysed specimens of the new species and its divergence as separate taxon ( Fig. 1A View Fig ). Most material used in the present study was from the Malay Peninsula, and the identities of other Southeast Asian populations will need to be examined in the future.