Leelumnus Mendoza & Ng, 2011, gen. nov.

Leelumnus gen. nov.

Type species. Leelumnus radium sp. nov., by present designation.

Diagnosis. Carapace transversely subhexagonal, broader than long; regions poorly defined; dorsal surface convex, smooth, sparsely setose. Front moderately projecting, bilobed; anterior margins gently concave, granulate, mesial angles more advanced than lateral, no lateral lobule visible. Fronto-orbital margin, epistome and buccal field relatively narrow transversely; fronto-orbital width about 0.4 times maximum carapace width. Orbits relatively short, rounded; eyes with short ocular peduncle. Anterolateral margin granulate; divided into 4 teeth; first tooth smallest, connected to exorbital angle by broad, horizontal, granulate crest; subsequent teeth projecting laterally, curving anteriorly, second tooth broadly triangular, third and fourth teeth narrower, acute. Chelipeds distinctly unequal, external surface of male major chela smooth, glabrous. Ambulatory legs smooth, without granules on margins of all articles; densely setose on carpi, propodi and dactyli. Male thoracic sternum and abdomen relatively broad; male telson triangular. G1 slender, slightly sinuous; distal tip flared/widened, flattened, covered with several simple, stiff, spiniform setae.

Etymology. The new genus is named in honor of Dr Lee Seng Tee. Through the Lee Foundation, he has been instrumental in helping the Raffles Museum and the National University of Singapore build a new natural history museum for the country. The genus name is formed by an arbitrary combination of his family name Lee and Pilumnus. Gender masculine.

Remarks. Although there is general consensus that the Pilumnoidea is a monophyletic entity (Ng et al. 2008), the classification of the various families is not satisfactory. On the basis of the carapace and general features, Leelumnus gen. nov. is best classified in the Pilumnidae Samouelle, 1819, primarily due to the presence of complete, well-defined longitudinal ridges on the endostome (endostomial crests), a relatively broader male abdomen with a semicircular telson, the G1 being long and sinuous, and the G2 is very short and sigmoid in shape (Ng 1998; Davie 2002; Ng et al. 2008). Leelumnus gen. nov. is superficially similar to Latopilumnus Türkay & Schuhmacher, 1985, and Aniptumnus Ng, 2002, in the following features: 1) the general form of the carapace, which is transversely subhexagonal, dorsally convex, relatively smooth and sparsely setose; 2) the absence of a lateral lobe on the frontal margin; 3) the quadridentate carapace anterolateral margin, where the two anterior teeth are relatively low and broad while the posterior two are more developed and acute; 4) the distinctly unequal chelipeds; and 5) the relatively broad male thoracic sternum and abdomen.

Leelumnus gen. nov. differs from Aniptumnus by 1) the absence of prominent granules on the distal border of the basis-ischium and the ventral border of the merus of P5 (Fig. 5 E) (vs. present); 2) having the anterior margins of the frontal lobes concave (Fig. 1, 2 A) (vs. straight or slightly convex); 3) having a relatively longer and more horizontal granulate crest between the first anterolateral tooth and exorbital angle (Fig. 1, 2 A) (vs. shorter and more oblique); 4) the proportionately narrower fronto-orbital margin, epistome and buccal fields, short and rounded orbits with proportionately smaller eyes, the fronto-orbital width being about 0.4 times the maximum carapace width (Fig. 2 A, B) (vs. wider, with relatively larger eyes, fronto-orbital width about 0.5 times maximum carapace width); 5) the relatively sharper, more angular internal infra-orbital tooth (Fig. 2 B) (vs. more rounded); 6) the relatively low orbital margins (Fig. 2 A, B) (vs. raised, appearing cristate); 6) the more triangular male telson with almost straight lateral margins (Figs. 2 C, 5D) (vs. semicircular with lateral margins rounded); 7) the distinctly flared/widened and flattened distal tip of the G1 (Fig. 5 G, I–J) (vs. blunt, but not flared or flattened); and 8) the proportionately smaller vulvae which do not reach sternal suture 5/6 and only have a small sternal cover (Fig. 4 A) (vs. relatively larger vulvae, touching sternite 5 with a large sternal cover; Fig. 4 B) (see Garth & Kim 1983: 706, fig. 11; Ng 2002: 213, fig. 1; Ng & Clark 2008: 901, 904, figs. 13, 14, 19–21).

Leelumnus gen. nov. is similar to Latopilumnus in the absence of prominent granules on the distal margin of the basis-ischium and the ventral margin of the merus of the last ambulatory leg (Fig. 5 E). In addition to the differences in the condition of the front, anterolateral margin, orbits, male telson and vulvae noted above for Aniptumnus, Leelumnus gen. nov. differs from Latopilumnus in having 1) the external surface of the major chela smooth (Fig. 3 A) (vs. prominently granular); 2) the dorsal margin of the ambulatory meri smooth (Fig. 5 E) (vs. granular or denticulate); 3) the ambulatory carpi without a distinct granulate, submedian, longitudinal ridge (vs. present); and 4) the distal tip of the G1 distinctly flared/widened and flattened (Fig. 5 G, I–J) (vs. tapering to a sharp point, sometimes recurved) (see Garth & Kim 1983: 709, fig. 12; Türkay & Schuhmacher 1985: 56, 58, figs. 1, 2, pl. 1, figs. 1– 4; Ng & Clark 2008: 886, figs. 1–12).

The relatively narrow front and general carapace features of Leelumnus gen. nov. superficially resemble species of the Indo-Pacific pilumnoid genus Parapanope De Man, 1895. However, members of this genus do not have endostomial crests, the anterolateral teeth are broader and more lobiform, the male abdomen is relatively more slender with the telson more elongate, and the G1 is more sinuous (Guinot 1985; Guinot & Ng 1988). Moreover, Parapanope is currently placed in the Galenidae Alcock, 1898 (Ng et al. 2008).

Comparative material. Aniptumnus quadridentatus (De Man, 1895): 6 males (6.7 × 4.4 mm – 14.6 × 10.0 mm), 6 females (7.9 × 5.3 mm – 11.0 × 7.1 mm) (ZRC 1989.3649–3660), from barnacle clumps on kelong pole, with mussels, Lim Chu Kang mangroves, Singapore. Aniptumnus vietnamicus Ng & Clark, 2008: Holotype male (7.9 × 5.7 mm) (ZRC 1970.1.10.1), paratype female (8.8 × 6.5 mm) (ZRC 1970.1.10.2), Nhatrang Bay, Vietnam, coll. R. Serène, 10 Apr. 1966. Latopilumnus conicus Ng & Clark, 2008: 2 male paratypes (3.3 × 2.3 mm, 3.9 × 2.8 mm), 2 females (4.8 × 3.3 mm, 5.0 × 3.4 mm) (ZRC 2003.0343), Conic Island Cave, 22º21´54˝N, 114º23´22˝E, Hong Kong, coll. 25 Oct. 2002. Latopilumnus malardi (De Man, 1914): paralectotype female (7.4 × 5.2 mm) (RMNH-D2187), in clumps of Balanus tintinnabulum (Cirripedia), Madagascar, coll. L.M. Malard, no date.