Leptarma schubarti, 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 : 208-212

publication ID	https://doi.org/ 10.26107/RBZ-2023-0016
publication LSID	lsid:zoobank.org:pub:FD7C342C-7EB1-43EF-AD03-0ACE87EC918B
persistent identifier	https://treatment.plazi.org/id/03E6654F-682F-FF8B-FC1A-91BBEDB9FDFA
treatment provided by	Felipe
scientific name	Leptarma schubarti
status	sp. nov.

Treatment

Leptarma schubarti View in CoL , new species

( Figs. 1–4 View Fig View Fig View Fig View Fig )

Material examined. Holotype: male (11.0 × 9.5 mm) ( ZRC 2019.1347 View Materials ), Rata Stream , flow to the Belmoul Lagoon, stn VM07, Espiritu Santo Island, Vanuatu, 15 ° 35′S, 167 ° 06′E, coll. 13 October 2006, SANTO 2006 Expedition GoogleMaps . Paratypes: 3 males (8.6 × 7.3 mm, 11.4 × 10.0 mm, 11.7 × 10.1 mm), 1 female (10.8 × 8.6 mm), 1 ovig. female (10.4 × 8.6 mm) ( ZRC 2017.0191 View Materials ), same data as the holotype GoogleMaps . Other material: 1 male (9.3 × mm), 1 ovig. female (10.7 × 9.2 mm) ( ZRC 2019.1343 View Materials ), stn. PAL 19-07, stream beside yam plantation, entry from bridge along main road, Ngetbong , Babeldaob Island, Palau, 7 ° 36′31.5″N, 134 ° 34′30.9″E, coll. 9 January 2019, B. Y. Lee & I. Iesa GoogleMaps ; 1 female (10.7 × 9.0 mm) ( ZRC 2019.1344 View Materials ), stn. PAL 19-11, mangrove on islet along highway on eastern Babeldaob Island , Palau, 7 ° 31′53.8″N, 134 ° 39′14.6″E, coll. 10 January 2019, B. Y. Lee & I. Iesa GoogleMaps .

Comparative material. Leptarma aurifrons (Li, Shih & Ng, 2019) : paratypes, 1 male (10.1 × 8.2 mm) ( ZRC 2019.0819); 9 males (9.8 × 8.2 mm – 11.1 × 9.5 mm), 4 females (10.7 × 8.4 mm – 11.5 × 9.1 mm) ( ZRC 2019.0822 View Materials ) ; 1 male (12.4 × 11.1 mm) ( ZRC 2019.0823 View Materials ) , 1 male (14.2 × 10.9 mm) ( ZRC 2019.1075 View Materials ) , Gankou River estuary, Hengchun , Pingtung, Taiwan. Leptarma gecko ( Li, Rahayu & Ng, 2018) : holotype male (16.5 × 14.3 mm) (RUMF-ZC-4710), Awase , Okinawa Island , Japan; paratypes 2 males (17.4 × 14.7 mm, 15.5 × 13.0 mm), 1 female (16.5 × 14.3 mm) (RUMF-ZC-2930), Yaeyama Islands , Iriomote Island, Japan ; 1 male (11.1 × 9.6 mm) ( ZRC 2019.1455 View Materials ) , stn. VM-04, intertidal, between Rose Point & Nasouli River, Espiritu Santo Island, Vanuatu, 15°34.9′S, 167°01.8′E, coll. SANTO 2006 Expedition, 11 September 2006 GoogleMaps ; 1 male (17.6 × 15.9 mm) ( ZRC 2019.1448 View Materials ) , stn. LBY 2019-16, sandy-muddy mangrove, Taveuni Island , Fiji, 16°49′28.6″S 179°52′16.6″W, coll. 25 July 2019, B. Y. Lee et al. Leptarma lenzii ( De Man, 1895) : lectotype male (13.3 × 11.3 mm) ( NNM-ZMA Crus. D. 102653) GoogleMaps , Aceh, Sumatra, Indonesia. Leptarma obliquifrons ( Rathbun, 1924) : holotype male (12.7 × 11.1 mm) ( USNM 45913 About USNM ) , Pago Pago , American Samoa. Leptarma reunionense Shahdadi & Schubart, 2020 : holotype male (12.2 × 10.1 mm) (MNHN- IU-2012-660), Mozambique Channel, Europa Island .

Diagnosis. Carapace slightly broader than long, front deflexed, slightly sinuous in dorsal view, median postfrontal lobes almost as wide as lateral ones, lateral carapace margin slightly concave; eye with peduncle short, stout, wider than long, cornea wider than peduncle; male chela large (homochelous), robust, upper surface of palm with two oblique pectinated crests, dorsal surface of dactylus with 15 low, blunt, 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, tip truncated, bent at an angle of about 50° to vertical axis, aperture terminal.

Description. (Morphometric measurements are for the holotype) Carapace subrectangular, slightly broader than long (cw/cl = 1.16), greatest width between exorbital angles; carapace surface smooth; front ca. 0.61 times carapace width, markedly deflexed, slightly sinuous in dorsal view; post-frontal lobes prominent, median lobes almost as wide as lateral ones, separated by shallow furrow; dorsal carapace regions well indicated, gastric region demarcated, cardiac region separated from intestinal region, lateral branchial ridges prominent; anterolateral margin with sharp exorbital angle, lateral margin slightly concave, lined with row of short setae. Eye with peduncle short, stout, wider than long, cornea wider than peduncle ( Figs. 1 View Fig , 2A View Fig , 3A View Fig , 4A View Fig ).

Male chela large (palm length/cw = 0.68), robust (palm width/ length = 0.59) ( Figs. 1 View Fig , 2D View Fig , 3A, E 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 18 well developed chitinous teeth, proximal one with 9–12 teeth, both crests terminate at inner end in 2 granules and granular rows on outer end ( Fig. 2E View Fig , 3F View Fig ); outer surface of palm with fine granules except for smooth, punctate fixed finger ( Figs. 2D View Fig , 3E View Fig ); inner surface of palm finely granular except area facing carpus and distal half of finger; no median vertical ridge ( Figs. 2E View Fig , 3F View Fig ); both sides of palm with scattered tufts of setae, cutting edge ca. 0.40 times palm length; dactylus ca. 0.60 time palm length, slightly curved downwards and inwards, dorsal surface with 15 (n = 5) low but distinct, transversely oval tubercles, distinct to tip, all tubercles positioned almost at median part of upper face of dactylus upper-inner side of dactylus scattered with small pointed granules ( Figs. 2E View Fig , 3F View Fig ); scattered tufts of setae on inner side, cutting edge of both fingers with a series of different sized teeth ( Figs. 2D View Fig , 3E View Fig ).

Ambulatory legs flattened dorso-ventrally, relatively long, third pair (P4) longest ( Figs. 1A, B View Fig , 3A View Fig , 4A View Fig ), total length (ischium–dactylus) ca. 1.9 times carapace width, tufts of long setae scattered along the legs, more on propodi and dactyli, merus of P4 ca. 2.41 times as long as wide, anterior margin crenulated, propodus ca. 3.27 times as long as wide, dactylus ca. 0.82 times length of propodus.

Male pleon triangular ( Figs. 1B View Fig , 2B View Fig ), with rounded telson, 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. 2C View Fig ).

G1 relatively long, stout, straight; apical corneous process long, narrow, tip truncated, bent at an angle of about 50° to vertical axis, aperture terminal ( Fig. 3B, C, D View Fig ).

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

Habitat and distribution. Most type material was collected from streams near the coast and also from mangroves, all on muddy substrates. The new species is thus far only known from Vanuatu and Palau .

Etymology. The new species is named in honour of Prof. Dr. Christoph D. Schubart (Universität Regensburg, Germany) for his significant contributions to brachyuran systematics, especially the family Sesarmidae .

Remarks. Besides the two new species described in the present study, two other species of Leptarma (i.e., L. gecko and L. obliquifrons ) have previously been recorded from oceanic islands in the Western Pacific ( Rathbun, 1924; Li et al., 2018). Leptarma schubarti , new species, differs most significantly from L. gecko in having proportionally shorter ambulatory legs (P4/cw = 1.9 in L. schubarti vs. P4/ cw = 2.2 in L. gecko ); and the apical corneous process of the G1 is uniformly narrow throughout its length and has a truncate tip ( Fig. 3B, C, D View Fig ) (vs. widening distally with the tip rounded in L. gecko, Li et al., 2018 : fig. 5D‒G). Li et al. (2018) mentioned that in L. gecko the number of dactylar tubercles on the male chela ranges from 10 to 15 (average 11), whereas L. schubarti has 15 dactylar tubercles consistently (n = 5) in the male chela. The shape of the proximal tubercles differs between these two species: they are low and blunt in L. schubarti ( Figs. 2D View Fig , 3E View Fig ), but steep and sharp in L. gecko ( Li et al., 2018, fig. 6D‒F). Leptarma gecko is a widely distributed species in the West Pacific, from Japan to New Caledonia and Fiji, and reportedly with intraspecific morphological variations ( Li et al., 2018). In the present study we also examined male specimens from Vanuatu and Fiji (see Comparative material), and both sufficiently resemble the types from Japan for them to be considered here as conspecific. However, to properly account for its wide distribution and morphological variations, a separate phylogeographic study using an appropriate genetic marker would clarify the true identities of material from its entire distribution range.

Leptarma schubarti differs from L. obliquifrons in possessing 15 (n = 5) small and broadly oval dactylar tubercles in the male chela ( Figs. 2D, E View Fig , 3E, F View Fig ) (vs. only 5–6 (n = 5) large and round tubercles in male L. obliquifrons, Li et al., 2019 : fig. 5D, E), and in the G1 apical corneous process being proportionately longer ( Fig. 3B View Fig ) than in L. obliquifrons ( Li et al., 2019: fig. 6A‒D).

The new species differs from L. lenzii s. str. in having a truncate G1 apical corneous process ( Fig. 3B, C, D View Fig ) (vs. tip widened and rounded in L. lenzii, Shahdadi et al., 2019 : fig. 1F‒I), and the operculum on the vulva is oval ( Fig. 4E View Fig ) (vs. triangular in L. lenzii, Shahdadi et al., 2019 : fig. 2).

Leptarma schubarti resembles the three Southeast Asian congeners, L. gracilipes ( Li, Rahayu & Ng, 2018) , L. macaco ( Li, Rahayu & Ng, 2018) , and L. tarantula ( Li, Rahayu & Ng, 2018) , in having a long and narrow apical corneous process of the G1 ( Li et al., 2018). The tip of the process, however, is rounded in these three species, while it is truncated in L. schubarti new species. The new species differs also from these species in the number of dactylar tubercles in the male chela (15 in L. schubarti (n = 5) vs. 7 or 8 in L. gracilipes (n = 2), 6‒8 (average 7) in L. macaco and 10‒12 in L. tarantula (n = 5) ( Li et al., 2018)).

According to the molecular results (see below; Fig. 12 View Fig ), L. schubarti is genetically closest to L. aurifrons (Li, Shih & Ng, 2019) . These two species, however, are quite different from each other in key morphological characters. Most significantly, the G1 has a short and wide apical process in L. aurifrons (cf. Li et al., 2019: figs. 3E, F, 4E), while it is nearly three times as long and narrower in L. schubarti ( Fig. 3B, C View Fig ). Leptarma aurifrons also has proportionally shorter ambulatory legs (P4/cw = 1.5 in L. aurifrons ; Li et al., 2019: figs. 2A, 3A) compared to the new species (vs. P4/cw = 1.9 in L. schubarti ; Figs. 1A View Fig , 3A View Fig , 4A View Fig ), the differences in length observed mainly in the ambulatory propodi. Furthermore, there are 12 subcircular dactylar tubercles in the male chela of L. aurifrons ( Li et al., 2019: fig. 4C), whereas there are 15 transversely oval dactylar tubercles in the male chela of L. schubarti ( Figs. 2D, E View Fig , 3E, F View Fig ).