Scandarma Schubart, Liu and Cuesta, 2003

Naruse, Tohru & Ng, Peter K. L., 2020, Revision of the sesarmid crab genera Labuanium Serène and Soh, 1970, Scandarma Schubart, Liu and Cuesta, 2003 and Namlacium Serène and Soh, 1970 (Crustacea: Decapoda: Brachyura: Sesarmidae), with descriptions of four new genera and two new species, Journal of Natural History (J. Nat. Hist.) 54 (7 - 8), pp. 445-532 : 474-476

Genus Scandarma Schubart, Liu and Cuesta, 2003

Scandarma Schubart, Liu and Cuesta, 2003, p. 50 ; Ng et al. 2008a, p. 223; Ng et al. 2017, p. 102.

Type species

Scandarma lintou Schubart, Liu and Cuesta, 2003 , by original designation. Gender neuter.

Included species

Scandarma lintou Schubart, Liu and Cuesta, 2003 ; Sc. finni ( Alcock, 1900) ; Sc. raymondi Ng, 2013 ; Sc. splendidum Naruse and Ng, 2007 ; Sc. gracilipes (H. Milne Edwards 1853); Sc. malagasy sp. nov.; Sc. papua sp. nov.

Diagnosis

Carapace squarish to subsquarish, wider than long; lateral margins parallel to weakly convex laterally, 0–2 rudimentary teeth behind external orbital angle; dorsal surface gently convex, regions weakly defined. Front deflexed at anterior margin of postfrontal lobes, distally recurved, directed anteriorly; frontal margin nearly straight to gradually concave medially, overhanging onto antennular septum and fossae. Two pairs of postfrontal lobes present (lateral lobes sometimes only feebly separated), lateral lobes slightly exceeding mesial lobes anteriorly ( Sc. gracilipes , Sc. lintou , Sc. papua , Sc. raymondi , Sc. splendidum ) or all lobes aligned anteriorly ( Sc. malagasy ); anterior margins of all lobes far from ( Sc. finni , Sc. malagasy , Sc. raymondi , Sc. splendidum ) or relatively close to ( Sc. gracilipes , Sc. lintou , Sc. papua ) but never reaching frontal margin in dorsal view. Antennular septum wide, short, dorsally covered by front. Orbit, in dorsal view, tilted J-shaped, median part of supraorbital margins oblique; inner orbital tooth triangular, short, directed dorsoanteriorly. No longitudinal ridge on ventral surface of external orbital angle. Epistome posterior margin with 3 triangular lobes, lateral lobes directed anteroventrally, median lobe directed ventrally ( Sc. gracilipes , Sc. lintou , Sc. malagasy , Sc. papua ) or lateral lobes directed ventrally, median lobe directed ventroposteriorly ( Sc. raymondi ). Antenna entering orbit through wide gap between inner orbital tooth and front. Mxp3 exopod with distinct flagellum. Chela palm with 1 nearly complete row of granules bordering outer and inner surfaces on upper surface ( Sc. gracilipes , Sc. lintou , Sc. papua , Sc. raymondi , Sc. splendidum ) or a few incomplete rows of granules bordering outer and inner surfaces ( Sc. malagasy ) in male and female; outer surface of chela with clearly delimited smooth slope towards bases of fingers, proximal to this slope with rounded to ridge-like protuberance ( Sc. gracilipes , Sc. lintou , Sc. raymondi , Sc. splendidum ) or slope less clearly delimited with lower protuberance ( Sc. malagasy , Sc. papua ); inner surface without transverse crest ( Sc. gracilipes , Sc. lintou , Sc. malagasy , Sc. papua , Sc. raymondi , Sc. splendidum ); thick rim extending along occlusal margin of immovable finger to dactylar articulation on both outer and inner surfaces, thick rims of both outer and inner surfaces not interrupted near dactylar articulation. Upper-inner margin of movable finger with a row of closely arranged small granules over proximal three-quarters ( Sc. gracilipes , Sc. lintou , Sc. papua ) or 1 row of sparsely aligned small granules ( Sc. malagasy , Sc. raymondi , Sc. splendidum ). Ambulatory legs (P2–5) relatively long, slender, dorso-ventrally flattened; distal anterior corner of each merus angled, not produced, followed proximally by subdistal tooth; carpi and propodi not distinctly narrower than respective meri; dactyli as long as or longer than half length of respective propodi. Male thoracic sternum transversely wide; sternite 8 clearly exposed. Male pleon wide ( Sc. gracilipes , Sc. lintou ) or relatively narrow ( Sc. malagasy , Sc. papua , Sc. raymondi , Sc. splendidum ) bell shaped, lateral margins of somites 3–5 forming a concave margin, telson slightly exceeding midlength of bases of cheliped coxae. G1 stout, relatively short, reaching midlength to distal end of thoracic sternite 5 in situ; beak-like and corneous process wide to narrow. Vulvae adjacent to thoracic sternal suture 5/6 on sternite 6, ellipsoidal, sternal vulval cover developed from anterolateral or posterolateral margin, convering almost entire to three-quarters of vulva.

Remarks

Scandarma was established for Sc. lintou Schubart, Liu and Cuesta, 2003 , from Taiwan. Naruse and Ng (2007); Ng (2013) subsequently described Sc. splendidum from Sarawak and Sc. raymondi from Sabah, respectively. The present study adds four more species to the genus (see below). Scandarma is characterised by the almost parallel and usually entire (or with 2 rudimentary teeth) lateral margins of the carapace, proportionally wide front ( Figures 15 (a), 18(a), 22(a), 24(a)), the presence of a distally sloping smooth area on the outer surface of the male cheliped palm towards the bases of the fingers ( Figures 16 (a), 18(b), 22(b), 24(c)), and relatively long and slender ambulatory legs ( Figures 15 (a), 18 (a), 22(a)). Scandarma is similar to Circulium in its moderately wide carapace and proportionally long legs. Scandarma , however, can be distinguished from Circulium by characters of the carapace, male chela, ambulatory legs and male pleon ( Table 1 ). The carapace contour of Scandarma is distinctly squarish, with almost parallel and usually entire (or with 1 or 2 rudimentary teeth) lateral margins ( Figures 15 (a), 18(a), 22(a), 24(a)). In Circulium , the lateral margin of the carapace is inflated laterally and dorsally around its branchial regions, appearing rounded, with usually 2 distinct teeth ( Figure 5 (a)). The male chela of Scandarma is unique in the presence of a distally sloping smooth area on the outer surface between the bases of the fingers ( Figures 16 (a), 18(b), 22(b), 24(c)), proximally having a rounded or ridge-like protuberance in most species ( Figures 16 (a), 18(b)), which is absent in Circulium ( Figure 6 (a)). Scandarma and Circulium share proportionally longer legs, but those of Scandarma are relatively more slender than in Circulium . The dactyli of the ambulatory legs are proportionally longer in Scandarma than in Circulium : the dactyli of Scandarma are as long as or longer than half the length of the respective propodi in P2– 5, rather than being shorter than half the length of the respective propodi in P 2–5 in Circulium .

In the present study, we recognise seven species, including two new species, of Scandarma . Of them, Sc. finni is certainly different from all other species of Scandarma , but its generic identity is not fully established, because the holotype, the only specimen of the taxon available for this study, is an immature female (see below). The taxon is treated as a species of Scandarma for the time being, as its characters best fit the genus. The following identification key includes six species, excluding Sc. finni as its male characters are not known.

Key to species of Scandarma (except for Sc. finni ( Alcock, 1900))

1. Anterior margins of postfrontal lobes relatively close to but never reaching frontal margin in dorsal view... ............................................................................................................................ 2

– Anterior margins of postfrontal lobes far from frontal margin in dorsal view... ...... 4

2. Outer surface of male chela with a weak protuberance proximal to smooth slope area around bases of fingers.. ......................................................................................... Sc. papua sp. nov.

– Outer surface of male chela with a strong protuberance proximal to smooth slope area around base of fingers.. ......................................................................................................... 3

3. Ambulatory legs relatively longer (P4 merus 0.79–0.89 times carapace length).. ............ ............................................................................................... Sc. lintou Schubart, Liu and Cuesta, 2003

– Ambulatory legs relatively shorter (P4 merus 0.76–0.78 times carapace length).. ....... ............................................................................................ Sc. gracilipes (H. Milne Edwards, 1853)

4. Upper surface of male cheliped palm without longitudinally traversing row of granules; G1 distal corneous process wide.. ................................ ............................... Sc. malagasy sp. nov.

– Upper surface of male cheliped palm with longitudinally traversing row of granules; G1 distal corneous process narrow.. ........................................................................................... 5

5. Upper surface of male cheliped palm with more widely spaced row of granules; granules on inner side of upper margin of male cheliped movable finger acute.. .............. ..................................................................................................................................... Sc. raymondi Ng, 2013

– Upper surface of male cheliped palm with more closely spaced row of granules; granules on inner side of upper margin of male cheliped movable finger rounded... ................................................................................................ Sc. splendidum Naruse and Ng, 2007

Figures

Figure 5. Circulium rotundatum (Hess, 1865). Neotype, USNM 1150304, male, 36.3 × 36.3 mm (Tonga). a, habitus, dorsal view; b, anterior part of cephalothorax, anteroventral view.

Figure 6. Circulium rotundatum (Hess, 1865). Neotype, USNM 1150304, male, 36.3 × 36.3 mm (Tonga). a, right chela, outer view; bright chela, upper view; c, cephalothorax, ventral view; d, meri of right P4 and P5.

Figure 15. Scandarma lintou Schubart, Liu and Cuesta, 2003. Paratype, ZRC 2002.0168, male, 19.0 × 19.6 mm (Taiwan). a, habitus, dorsal view; b, anterior part of cephalothorax, anteroventral view.

Figure 16. Scandarma lintou Schubart, Liu and Cuesta, 2003. Paratype, ZRC 2002.0168, male, 19.0 × 19.6 mm (Taiwan). a–c, left chela; a, outer view; b, inner view; c, upper view; d, meri of right P4 and P5.