Vellumnus, Ng, Peter K. L., 2010

Ng, Peter K. L., 2010, On the Planopilumnidae Serène, 1984 (Crustacea: Brachyura: Pseudozioidea), with diagnoses of two new pilumnoid genera for species previously assigned to Planopilumnus Balss, 1933, Zootaxa 2392, pp. 33-61 : 50-51

Vellumnus new genus

Type species. Pilumnus labyrinthicus Miers, 1884 , by present designation.

Diagnosis. Carapace broader than long ( Figs. 13A , 14A , 15 A); carapace, pereiopods covered with dense, short, soft pubescence as well as scattered long plumose setae completely obscuring surfaces ( Figs. 13A , 14A , 15 A); dorsal carapace regions convex, separated by shallow grooves ( Figs. 13A , 15 A); epigastric, mesogastric, postorbital cristae short, distinct but not always easily separated from other carapace ridges or swellings ( Figs. 13A , 15 A); posterolateral, posterior carapace, sub-branchial regions with scattered granules or ridges but never forming discrete channels ( Fig. 15 A). Frontal margin with 2 subtruncate lobes separated by fissure or cleft; separated from supraorbital margin by distinct lateral lobule; supraorbital margin gently concave with single fissure ( Figs. 14A , 15 A). Suborbital margin concave with low inner, outer teeth, not cristate ( Figs. 13B , 16 A). Anteroexternal angle of third maxilliped distinct but not auricuiliform ( Figs. 14C , 16 B). External orbital tooth triangular, usually low; anterolateral margin with 3 subequal teeth, sometimes appearing sublobiform ( Figs. 13A , 14A , 15 A). Chelipeds in adult males, females subequal or with one chela larger ( Figs. 13A , 15 A); surfaces of articles with scattered granules, without prominent ridges; usually covered with dense short, long setae almost completely obscuring surfaces; fingers glabrous ( Figs. 13A , 15 B). Ambulatory legs without distinct crests or ridges; surfaces completely obscured by numerous long, short setae ( Figs. 13A , 15 A). Anterior thoracic sternum relatively narrow, surfaces relatively smooth, or with scattered small granules ( Figs. 14B , 16 C); sternites 1, 2 completely fused without trace of suture; s2/3 complete; s3/4 almost complete but medially very shallow, almost undiscernible; s4/5, s5/6, medially interrupted; s6/7, s7/8 complete; longitudinal median groove present from sternites 6-8; male press button distinct, positioned on anterior part of sternite 5. Male abdomen relatively narrow, outer surfaces almost smooth; all abdominal somites, telson mobile ( Fig. 16 D). G1 very slender, sinuous, distal part tapering to sharp or rounded tip ( Figs. 15 C–E, 16E–G, I, J). G2 about one fifth or less length of G1 ( Figs. 15 F, 16H).

Etymology. The name is derived from the Latin "vellus" for fleece; in arbitrary combination with the genus Pilumnus . The gender of the genus is masculine.

Remarks. Five species are referred here to Ve ll u mnu s new genus: V. labyrinthicus ( Miers, 1884) , V. vermiculatus (A. Milne Edwards, 1873) , V. penicillatus ( Gordon, 1930) , V. minabensis ( Sakai, 1969) , and V. pygmaeus ( Takeda, 1977) . On the basis of their original descriptions and/or examination of material, there is no doubt they are pilumnids as defined by Ng et al. (2008). The slender S-shaped G1 with the very short and sigmoidal G2 is particularly diagnostic. The labyrinth-like pattern of setae on the dorsal surface of the carapace is most pronounced in V. labyrinthicus ( Fig. 13A ), and the ridges underlying these setae are also strongest in this species ( Fig. 15 A). In other species, notably V. penicillatus , the setae are neither as dense or the underlying ridges as strong as in V. labyrinthicus . Vellumnus vermiculatus is peculiar in that the carapace setae are longer and concentrated along the anterolateral and frontal regions, with the surfaces below relatively more swollen rather than ridge-like. The figures provided for Pilumnus vermiculatus by A. Milne- Edwards (1873: 247, pl. 9 fig. 6) are somewhat schematic and do not show all the features of the species well. The types of V. vermiculatus examined actually more closely resemble species of Heteropilumnus De Man, 1895 , and to some degree, Cryptocoeloma Miers, 1884 (see Ng 1987, 1989). Interesting, A. Milne-Edwards (1873: 247, 248) in his description and discussion, compares the species with Pilumnus fimbriatus H. Milne Edwards, 1834 , a taxon currently placed in Heteropilumnus . However, the form of its carapace and the presence of well defined anterolateral teeth suggest that transferring this species to the Pilumnidae may be premature. For the moment, it is retained in Vellumnus as an atypical member of the genus

Comparative material. Vellumnus penicillatus ( Gordon, 1930) : 1 male (6.7 × 5 mm)( ZRC 1965.7.8.13), dredge, 20–30 m, Pulau Pawai, Singapore, coll. Nov. 1933; Vellumnus vermiculatus ( A. Milne-Edwards, 1873) : syntypes, 3 dried females (1 ovigerous) ( MNHN B2848), New Caledonia, coll. Balansa.

Figures

FIGURE 15. Vellumnus labyrinthicus (Miers, 1884). A, B, paralectotype male (9.0 × 8.0 mm) (NHM 1882: 93); C – G, 1 male (9.0 × 8.0 mm) (ZRC 1983.10.14.1). A, overall view (carapace partly denuded); B, outer view of left chela; C, left G 1 (ventral view); D, distal part of left G 1 (ventral view); E, distal part of left G 1 (dorsal view); F, left G 2; G, distal part of left G 2. Scales: C, F = 0.5 mm; D, E, G = 0.07 mm.

FIGURE 16. Vellumnus labyrinthicus (Miers, 1884). A – D, male (13.5 × 10.8 mm) (ZRC 1999.397); E – H, lectotype male (8.5 × 6.8 mm) (NHM 1882.165); I, J, male (13.9 × 10.0 mm) (ZRC). A, frontal view showing orbits, epistome, antennule and antenna (denuded); B, right third maxilliped (denuded); C, right side of anterior thoracic sternum (denuded); D, abdomen (denuded); E, left G 1 (ventral view); F, I, distal parts of left G 1 s (ventral views); G, J, distal parts of left G 1 s (dorsal views); H, left G 2. Scales: A, C – E, H = 2.0 mm; B = 1.0 mm; F – H, I, J = 0.5 mm.

FIGURE 13. A, B, Vellumnus labyrinthicus (Miers, 1884), paralectotype female (15.8 × 13.0 mm) (NHM 1882.165 b); C, Colerolumnus fuscus (Balss, 1933), lectotype male (7.3 × 5.4 mm) (ZMB 23359. A, C, dorsal overall views; B, frontal view of carapace.

FIGURE 14. A – C, Vellumnus labyrinthicus (Miers, 1884), male (13.5 × 10.8 mm) (ZRC 1999.397); D, Colerolumnus fuscus (Balss, 1933), lectotype male (7.3 × 5.4 mm) (ZMB 23359). A, D, right side of denuded dorsal surfaces of carapaces; B, anterior thoracic sternum (denuded); left third maxilliped (denuded).