Leptarma bertrandi, Shahdadi & Mendoza, 2023

Shahdadi, Adnan & Mendoza, Jose Christopher E., 2023, Two new species of the mangrove crab genus Leptarma (Crustacea: Brachyura: Sesarmidae) from the Western Pacific islands, Raffles Bulletin of Zoology 71, pp. 207-223 : 213-217

publication ID	https://doi.org/ 10.26107/RBZ-2023-0016
publication LSID	lsid:zoobank.org:pub:FD7C342C-7EB1-43EF-AD03-0ACE87EC918B
DOI	https://doi.org/10.5281/zenodo.7815637
persistent identifier	https://treatment.plazi.org/id/03E6654F-6828-FF87-FEBC-917BE88EF7B2
treatment provided by	Felipe
scientific name	Leptarma bertrandi
status	sp. nov.

Treatment

Leptarma bertrandi View in CoL , new species

( Figs. 5–8 View Fig View Fig View Fig View Fig , 9A‒D View Fig , 10A‒D View Fig , 12A‒C View Fig )

Parasesarma lenzii View in CoL — Li et al., 2019: 19, fig. 12A, B. Not Leptarma lenzii ( De Man, 1895) View in CoL .

Material examined. Holotype: 1 male (21.4 × 19.3 mm) (MNHN-IU-2022-384), mangrove, Ouvéa Island , Loyalty Islands, New Caledonia, 20 ° 24.5′S, 166 ° 34′E, coll. 10 December 2009, KIWA 2 Expedition GoogleMaps . Paratypes: 2 males (18.0 × 15.2 mm, 16.5 × 14.2 mm), 1 female (18.6 × 16.0 mm) ( ZRC 2019.1330 View Materials ), same data as the holotype GoogleMaps . Other material: 1 male (14.5 × 12.5 mm) ( ZRC 2019.1331 View Materials ), intertidal, sand and muddy sand, station VM09, Belmoul Lagoon , Espiritu Santo Island, Vanuatu, 15 ° 35.8′S, 167 ° 06.1′E, coll. 13 October 2006, SANTO 2006 Expedition GoogleMaps ; 6 males (8.8 × 7.6 mm – 17.8 × 15.7 mm), 2 females (14.8 × 13.0 mm, 18.3 × 16.2 mm) ( ZRC 2019.1079 View Materials ), Tanzih fish port, Pingtung, Taiwan, coll. 29 September 2018, J.-J. Li .

Comparative material. Leptarma lenzii ( De Man, 1895) : lectotype, male (13.3 × 11.3 mm) ( NNM-ZMA Crus. D. 102653), Aceh, Sumatra, Indonesia; 1 male (16.4 × 14.2 mm) ( ZRC 2018.1374 View Materials ), Cocos (Keeling) Islands ; 1 male (11.8 × 9.9 mm), 2 females (15.1 × 13.4 mm, 8.3 × 7.3 mm) ( ZRC 2018.1373 View Materials ), Cocos (Keeling) Islands .

Diagnosis. Carapace slightly broader than long, front deflexed, slightly sinuous in dorsal view, median postfrontal lobes wider than lateral ones, carapace lateral margin almost straight; eye with peduncle short, stout, wider than long, cornea wider than peduncle; male chela large, robust, upper surface of palm with two oblique pectinated crests, dorsal surface of dactylus with 8‒10 transversely oval tubercles, distinct to tip, proximal tubercles positioned at almost median part of upper face of palm; ambulatory legs flattened dorsoventrally and relatively long, third pair (P4) longest, total length (ischium–dactylus) ca. 1.9 times carapace width; male pleon triangular, somite 2 medially longer than lateral edges; G1 robust, long, straight, apical corneous process long, stout, tip rounded, bent at an angle of about 50° to vertical axis, aperture subterminal.

Description. (Morphometric measurements are for the holotype) Carapace subrectangular, slightly broader than long (cw/cl = 1.10); carapace surface smooth; front ca. 0.60 times carapace width, markedly deflexed, slightly sinuous in dorsal view; post-frontal lobes prominent, median lobes wider than lateral ones, separated by shallow furrow; dorsal carapace regions well indicated, gastric region demarcated, cardiac region separated from intestinal region, lateral branchial ridges prominent, in the largest male (holotype) first ridge results in an epibranchial (anterolateral) prominence (posterior to exorbital angle); anterolateral margin with sharp exorbital angle, lateral margin almost straight, lined with row of short setae. Eye with peduncle short, stout, wider than long, cornea wider than peduncle ( Figs. 5A View Fig , 6A, B View Fig , 7A View Fig , 9A‒D View Fig ).

Male chela large (palm length/cw = 0.76), robust (palm width/ length = 0.56) ( Figs. 5 View Fig , 6C View Fig , 10A–D View Fig ); merus with granulate dorsal border, no distinct subdistal spine, ventral border granulate, anterior border granulate, with distinct subdistal spine; upper surface of palm with 2 oblique pectinated crests, distal one composed of 10–12 (10 in holotype) well-developed chitinous teeth, proximal one with 6–10 (10 in holotype) teeth, both crests terminate at inner end in 2 granules and granular row on outer side; outer surface of palm with coarse granules except for smooth, punctate fixed finger; inner surface of palm finely granular except area facing carpus and distal half of finger; no median vertical ridge; both sides of palm with scattered tufts of setae, cutting edge ca. 0.41 times palm length, with a series of different sized teeth; dactylus ca. 0.57 times palm length, slightly curved downwards and inwards, dorsal surface with 8‒10 (n = 5) (nine in holotype) distinct, transversely oval tubercles, distinct to tip, all tubercles including the proximal ones positioned almost at median part of upper face of palm; small pointed granules scattered on inner and outer side; cutting edge with two large and a series of smaller teeth ( Figs. 5A View Fig , 6C‒E View Fig , 10A‒D View Fig ).

Ambulatory legs flattened dorso-ventrally, relatively long, third pair (P4) longest ( Figs. 5 View Fig , 7A, B View Fig , 9A‒D View Fig ), total length (ischium–dactylus) 1.9 times carapace width, tufts of long setae scattered along the legs, more on propodi and dactyli, merus of P4 ca. 2.40 times as long as wide, anterior margin crenulated, propodus ca. 3.6 times as long as wide, dactylus ca. 0.66 times length of propodus.

Male pleon triangular, with rounded telson ( Figs. 5B View Fig , 6F View Fig ), almost as wide as long, almost as long as somite 6; somite 6 longer than others; somites 4 and 5 trapezoidal, somite 3 widest, laterally convex, somite 2 medially longer than lateral edges ( Fig. 6G View Fig ).

G1 relatively long, stout, straight; apical corneous process long, tip rounded, distally flared, bent at angle of about 50° to vertical axis, aperture sub-terminal ( Figs. 6H‒J View Fig , 11A‒C View Fig ).

Female ( Fig. 7 View Fig ) with proportionately smaller chelipeds; pectinate crests reduced to rows of granules ( Fig. 7C, D View Fig ); except for few proximal ones, dactylar tubercles indistinct ( Fig. 7C, D View Fig ). Pleon broad, rounded, or even laterally slightly ovate, broadest at somite 4, fringed with long setae ( Fig. 7B View Fig ). Vulva in depression on anterior edge of sternite 6, touching posterior margin of sternite 5; operculum triangular, perpendicular, positioned anterior to gonopore ( Fig. 7E View Fig ).

Habitat and distribution. Specimens of this species were collected from mangroves and estuaries, in the intertidal zone, on sand or muddy sand substrates. The new species is known thus far from the Loyalty Islands ( New Caledonia), Vanuatu (present study), and Taiwan ( Li et al., 2019; present study).

Etymology. This new species is named in honour of Dr. Bertrand Richer de Forges for his tireless efforts in collecting and documenting the brachyuran/crustacean fauna of the Indo-West Pacific region, particularly through expeditions held under various French-led marine biodiversity programs.

Remarks. Leptarma bertrandi , new species, most closely resembles L. lenzii s. str. in general appearance. According to our molecular results, these two species also have a close phylogenetic association (see below). These two species, however, differ in several morphological characters. The dorsal carapace regions are more demarcated in L. bertrandi ( Fig. 9A–D View Fig ) than in L. lenzii ( Fig. 9E, F View Fig ). The lateral frontal lobes are distinctly narrower than the median ones in L. bertrandi ( Figs. 6A, B View Fig , 9A–D View Fig ), while they are subequal in L. lenzii ( Fig. 9E, F View Fig ). These two species also differ in the pattern of the dactylar tuberculation in the male chela, the new species only having 8‒10 (n =5) distinct tubercles ( Fig. 10A–D View Fig ), while L. lenzii has 11–13 (n = 3) small tubercles ( Fig. 10E, F View Fig ). The new species ( Fig. 9A–D View Fig ) has proportionally longer ambulatory legs than L. lenzii ( Fig. 9E, F View Fig ), especially the propodi: i.e., length of P4 (ischium–dactylus) = 1.9 times carapace width, merus ca. 2.4 times as long as wide, propodus ca. 3.6 times as long as wide, dactylus ca. 0.66 times length of propodus in L. bertrandi ; while in L. lenzii the corresponding values are P4 = 1.8 times cw, merus ca. 2.2 times as long as wide, propodus ca. 2.9 times as long as wide, dactylus ca. 0.60 times length of propodus. The two species are similar in the general form of the G1, but the apical corneous process of L. bertrandi ( Fig. 11A–C View Fig ) is distinctly shorter and stouter than that of L. lenzii ( Fig. 11D, E View Fig ). It bears noting here that the material from Taiwan previously reported as Parasesarma lenzii (viz. Li et al., 2019: 19), is here treated as conspecific with L. bertrandi , primarily due to it possessing the diagnostic morphology of the ambulatory legs, male chela, and G1.

Furthermore, the live colouration of the two species may be useful for differential diagnosis, based on the information gleaned from available colour photographs of these crabs. The L. bertrandi from Taiwan has orange chelae with deeper reddish-orange fingers and a predominantly whitish carapace with black marbling ( Li et al., 2019, fig. 12A, B); the colour patterns on the specimen from Vanuatu ( Fig. 8 View Fig ) are similar, but the specimen was photographed only after it had been in the freezer overnight and the colour may have already faded. On the other hand, L. lenzii from the Cocos (Keeling) Islands has greyish chelae with orange-tipped fingers ( Shahdadi et al., 2019, fig. 3D) and a predominantly black carapace with small yellow spots and a distinct yellow, transverse, submarginal band on the frontal region ( Shahdadi et al., 2019, fig. 3C, D). This will need further investigation as more fresh material is observed.