Namlacium crepidatum ( Calman, 1925 )

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 : 519-523

Namlacium crepidatum ( Calman, 1925)

( Figures 35–37 )

Sesarma crepidatum Calman, 1925, p. 454 [type locality: Papua New Guinea].

Namlacium crepidatum: Serène and Soh 1970, p. 404 ; Manning and Holthuis 1981, p. 242; Ng et al. 2008a, p. 221.

Material examined

Holotype. NHM 1925.1.29.1, male, 12.5 × 15.4 mm, Papua New Guinea, coll. P.J. de Verteuil, 30 May 1924.

Redescription

Carapace ( Figure 35 (a)) subcircular with convex lateral margins, 1.23 times as wide as long. Dorsal surface weakly convex longitudinally and transversely, glabrous, regions moderately defined. Posterolateral regions sloping. Front narrow, entire, about one-third of frontorbital width, deflexed at anterior margin of postfrontal lobes, distally recurved, directed anteriorly; frontal margin entire, straight in dorsal view, overhanging onto antennular septum and fossae ( Figure 36 (a)). One pair of postfrontal lobes present, these lobes far from frontal margin; lateral part of front with longitudinal low cristae consisting of row of 3 small granules. External orbital angle very sharp, long, weakly upcurved distally, directed anteriorly; no trace of epibranchial tooth. Antennular septum ( Figure 36 (a)) narrow, short. Orbit, in dorsal view, deep J-shaped, median part of supraorbital margins oblique ( Figure 35 (a)); infraorbital margin ( Figure 36 (a)) cristate, with triangular inner orbital tooth, directed anteriorly. Suborbital crista straight, granulated, setose. Suborbital, pterygostomial, subhepatic regions with reticulate mat of setae. No longitudinal ridge on ventral surface of external orbital angle.

Epistome ( Figure 36 (a)) relatively long, posterior margin with 3 triangular lobes, lateral lobes sharply pointed, directed anteroventrally, median lobe directed ventrally. Endostomial ridge developed from mesial margin of posterolateral lobe of epistome.

Eye ( Figures 35 (a), 36(a)) large; cornea dilated. Antennule with narrow, vertically high basal article. Antenna with small basal article, distolateral lobe narrow, short; antenna entering orbit through space between inner orbital tooth and front.

Mxp3 ( Figure 35 (b)) leaving wide gape between mesial margins of ischiaand meri; ischium rectangular, as long as merus; merus ovoid, with oblique depression mesially lined with setae, setose around base of carpus; dactylus missing. Exopod reaching distal third of merus, with long flagellum reaching mesial margin of merus.

Chelipeds ( Figures 35 , 36 (a)) subequal and similar. Meri with trigonal cross section; upper margin weakly cristate, granulate; except for distal end; lower-inner margin sparsely serrate; lower-outer margin weakly cristate, sparsely serrate distally; outer surface with short rows of granules; inner surface smooth, with one longitudinal row of soft setae near lower margin. Carpi ( Figure 36 (c)) rhomboidal in upper view, inner angle rounded, inner margin with tuft of long setae on posterior to inner angle. Palm of chela swollen; upper surface ( Figure 36 (a,c)) with short to long, interrupted longitudinal rows of weak granules on upper surface extending from hinge with carpus to inner base of dactylus; granules scattered on upper to outer surfaces larger than those forming longitudinal rows; outer surface ( Figure 36 (b)) generally convex, granulated (granules becoming smaller on lower part) except for slightly depressed area around base of fingers, low oblique protuberance proximal to this depressed area; inner surface convex, upper half smooth, lower half granulated, bearing C-shaped row of large tubercles extending from inner side of distal upper corner to median part of inner surface of palm; 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. Immovable finger almost straight, directed slightly downwards, gradually tapering, occlusal margin with 2 large teeth submedially, slightly smaller tooth subdistally, and much smaller teeth on proximal quarter; movable finger gently arched, occlusal margin bearing large tooth subdistally, smaller teeth on proximal twofifths, margin between subdistal and proximal teeth concave; upper margin sparsely lined with low granules over proximal half; tips of both fingers corneous, sharply pointed but weakly hoof-like on occlusal side; largest tooth of movable finger located posterior to second largest tooth of immovable finger when fingers closed.

Ambulatory legs ( Figures 35 (a), 36(d,e)) very long, slender, P3 and 4 longest. Small tufts of soft setae on anterior surfaces of P2–5 coxae. Meri strongly compressed, and then upper surface narrow; distal anterior corner of merus forming strong triangular projection, anterior and posterior margins bearing sharp subdistal tooth on each P2–5, followed proximally by weak, sparse serration in P2–4, smooth in P5. Carpi outer margin sparsely lined with weak granules. Propodi each with subparallel inner and outer margins; inner surfaces lined with rows of long setae. Dactyli very short, proximally bent inward almost perpendicularly, extensor surface covered with dense mat of brushlike, stiff setae.

Male thoracic sternum ( Figure 35 (b)) transversely wide, thoracic sternites 1–4 fused, sternites 2/3 and 3/4 demarcated superficially by anteriorly convex and concave grooves, respectively. Sternopleonal cavity reaching proximal half of bases of cheliped coxae; margin of sternopleonal cavity on somite 4 rimmed except for posterior end, posterior end of this rim thickened; lateral slope of sternopleonal cavity posterior to non-rimmed part of sternite 4 depressed, accomodating distal end of G 1 in situ. No sternal button for locking mechanism on sternite 5. Penis sternal.

Male pleonal somites 1, 2 short, similarly wide; somite 3 widest, somite 3 to proximal two-thirds of somite 6 gradually narrowed, lateral margins almost straight; telson rounded distally, slightly longer than somite 6 ( Figures 35 (b), 37(a)).

G1 ( Figure 37 (b,c)) short, stout, slightly constricted medially, slightly curved outward distally, terminal process corneous, rectangularly beak-like, directed distolaterally. G2 ( Figure 37 (d)) short.

Colouration

Living colouration not known.

Distribution

Known only from the type locality, Papua New Guinea. In describing this species, Calman (1925, p. 454) stated only that

The specimen described below was collected in New Guinea by Mr. P.J. de Verteuil and was presented to the Museum by the Imperial Bureau of Entomology. Unfortunately, there is no information as to the exact locality, habitat, or habits of the crab.

A search of the literature shows that there was a well-known geologist by the name of J. P. de Vertueil who worked in the eastern part of the island of New Guinea (today Papua New Guinea) searching for oil and gas deposits in the 1920s to 1930s ( Gray and de Verteuil 1930; Mayo and de Verteuil 1930a, 1930b, 1930c; Mayo et al. 1930a, 1930b; de Verteuil 1930). This is almost certainly the same man as Calman’s ‘P.J. de Verteuil’, and as such, we are quite certain the type specimen of this species was collected somewhere in the eastern part of what is today Papua New Guinea.

Ecological note

Calman (1925, p. 456) writes: ‘the remarkable furred moccasins on its feet are unlike anything known to me among the Brachyura, and have the appearance of being an adaptation to running over soft mud’. Serène and Soh (1970) noted that the dense brushes of setae on the ambulatory dactyli were not different from those in species at that time assigned to Labuanium , but they are incorrect. The ambulatory setae are much denser and concentrated on the extensor margin of the dactylus in Namlacium (vs more evenly spread and denser on the flexor margins in Labuanium s.l.). It is not known whether N. crepidatum has arboreal habits, but the short ambulatory dactyli would suggest so. So far, all sesarmid species which have short to very short ambulatory dactyli are known to have arboreal tendencies or habits (see also Schubart et al. 2009; Li et al. 2018).

Figures

Figure 35. Namlacium crepidatum (Calman, 1925). Holotype, NHM 1925.1.29.1, male, 12.5 × 15.4 mm (New Guinea). a, habitus, dorsal view; b, cephalothorax, ventral view.

Figure 36. Namlacium crepidatum (Calman, 1925). Holotype, NHM 1925.1.29.1, male, 12.5 × 15.4 mm (New Guinea). a, cephalothorax and chelipeds, frontal view; b, right chela, outer view; c, right chela, upper view; d, left P3 to P5, upper view; e, left P3 to P5, lower view.

Figure 37. Namlacium crepidatum (Calman, 1925). Holotype, NHM 1925.1.29.1, male, 12.5 × 15.4 mm (New Guinea). a, pleon and telson; b, left G1, ventral view; c, distal part of left G1, ventral view; d, G2, ventral view. Scale bars: a= 3 mm; b–d = 1 mm.