Labuanium Serène and Soh, 1970

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 : 447-448

Genus Labuanium Serène and Soh, 1970

Labuanium Serène and Soh, 1970, p. 401 ; Davie 2002, p. 221; Ng et al. 2008a, p. 221; Ng et al. 2015a, p. 1; Ng et al. 2017, p. 102.

Type species

Sesarma polita De Man, 1887 , by original designation. Gender neuter.

Included species

Labuanium politum (De Man, 1887) .

Diagnosis

Carapace elongated, rectangular, longer than wide; lateral margins sinuous, with 1 distinct epibranchial tooth behind external orbital angle; dorsal surface flat, regions well defined. Front deflexed at anterior margin of postfrontal lobes at more than 90°, distally sloping ventroposteriorly; frontal margin bilobed with wide median concavity, each lobe recurved, directed anteriorly, median concave part attached to wide, long, clearly exposed antennular septum. Two pairs of postfrontal lobes aligned anteriorly, all lobes projected anteriorly, overhanging onto front, anterior margins lined with small spinules, followed posteriorly by a few transverse rows of spinules; mesial lobes about 2 times wider than lateral lobes. Orbit, in dorsal view, medially low W-shaped, median part of supraorbital margins oblique; inner orbital tooth short, subtriangular, directed dorsoanteriorly. No longitudinal ridge on ventral surface of external orbital angle. Epistome posterior margin with 3 low lobes, all terminally directed anteriorly. Antenna entering orbit through wide gap between inner orbital tooth and front. Mxp3 exopod with distinct flagellum. Chela palm of male and female with randomly lined granules but without complete longitudinal ridge on upper surface; outer surface granulated but without prominent protuberance; inner surface without transverse rows of granules; 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 interrupted near dactylar articulation. Upper-inner margin of movable finger of male and female with 1 row of sparsely, irregularly lined small, sharp granules over proximal two-thirds. Ambulatory legs (P2–5) moderately long, dorso-ventrally flattened, wide; distal anterior corner of each merus angled, followed proximally by subdistal tooth; carpi and propodi not distinctly narrower than respective meri; dactyli shorter than half length of respective propodi. Male thoracic sternum transversely narrow; sternite 8 clearly exposed. Male pleon narrow, telson exceeding proximal half of bases of cheliped coxae (reaching distal three-quarters). G1 relatively stout, straight, short, reaching only midlength of thoracic sternite 6; distal beak-like process relatively narrow. Vulvae opening near middle on sternite 6, ellipsoidal; sternal vulval cover developed from lateral margin, subcylindrical, covering lateral three-quarters of vulva.

Remarks

Labuanium politum is very characteristic in its longitudinally rectangular carapace, wide and long ambulatory legs with short dactyli and proportionately narrow male pleon. Moreover, the front of the carapace is strongly bent ventroposteriorly so that the median concavity of the frontal margin is attached to the antennular septum, and the postfrontal lobes form the anterior margin of the carapace. Labuanium politum is also unique in that the rims extending along the occlusal margin of the immovable finger are interrupted near the dactylar articulation on both outer and inner surfaces. These and other characters listed in Table 1 set L. politum apart from other allied species. The present study restricts Labunanium s.s. to L. politum . Other species which have been placed in this genus by Serène and Soh (1970) and subsequent authors are now transferred to Circulium gen. nov., Scandarma Schubart, Liu and Cuesta, 2003 , Shinobium gen. nov., Mindanium gen. nov. and Geosesarma (see Table 1 and remarks under these taxa).