Vellumnus penicillatus (Gordon, 1930)

(Figs. 1–3)

Pilumnus penicillatus Gordon, 1930: 523 . — Gordon, 1931: 542, fig. 18. — Balss, 1933: 12.

“ Pilumnus ” penicillatus — Ng et al., 2008: 142, 145.

Material examined. Holotype female (4.2 × 2.9 mm) (NHM 1930.12.2.123), Hong Kong, Barney collection . Paratypes: male (3.6 × 2.9 mm) (NHM 1930.12.2.124), ovigerous female (5.3 × 3.7 mm) (NHM 1030.12.2.124), same data as holotype.

Diagnosis. Carapace hexagonal, wide; surface and pereiopods covered with dense, short, soft pubescence as well as scattered long plumose setae completely obscuring margins and surfaces, longer setae arranged in clumps on carapace regions, forming faint circular patterns on gastric regions (Figs. 1A, B, 2C, 3A); epigastric, mesogastric, postorbital cristae low, gastric, subhepatic, branchial regions with scattered low granules (Figs. 1A, B, 2C, 3A); frontal margin gently convex to sinuous, lateral lobe low but distinct; supraorbital margin with prominent median fissure(Fig. 3A–C); external orbital tooth triangular, subtruncate, first anterolateral tooth triangular or bilobed, third tooth smallest (Fig. 3A–C); anteroexternal angle of merus of third maxilliped distinct but not auriculiform, ischium with shallow oblique sulcus (Fig. 3E); outer surface of chelae with numerous round granules, vaguely arranged in longitudinal rows, carpus with numerous round granules, without distinct tooth on inner angle, fingers shorter than palm (Fig. 2A, B); ambulatory legs without distinct crests or ridges; surfaces completely obscured by numerous setae (Figs. 1A–C); anterior thoracic sternum with surfaces relatively smooth, no trace of separation between sternites 3 and 4 except for lateral sutures (Figs. 1C, 3F); tubercle of sterno-pleonal locking mechanism round, on anterior third of sternite 5 (Fig. 3F); male pleon relatively narrow; somite subrectangular, somites 1, 3 subequal in width, telson semicircular (Figs. 1C, 3G); G1 slender, sinuous, distal part bent laterally with sharp tip (Fig. 3H, I).

Distribution. Hong Kong (Gordon, 1930).

Remarks. Vellumnus penicillatus is here described in detail with additional figures. The dorsal surface of the carapace comprises dense setae arranged in approximate patterns (Figs. 2C, 3A) but is without underlying ridges, the surface is generally smooth with only scattered granules on the lateral parts(Fig. 1A, B).

Takeda (1977a: 131) listed a number of characters that distinguished V. penicillatus from V. pygmaeus (type locality: Ogasawara Islands): “the median gastric region is indicated by a longitudinal strand ending in a diamond, a tomentum on each protogastric region forms a circle or ocellus, the areolation beneath the tomentum is only faintly indicated, the carapace is apparently broader with the nearly truncated second and third anterolateral teeth, the latter of which forms the lateral angle of the carapace, and the male first pleopod bears a strong subdistal spine.” His carapace setal patterns, however, do not appear to be a good character because the original figure by Gordon (1931) is somewhat schematic (present Fig. 3A). The two species, however, are different; in V. penicillatus, the supraorbital and anterolateral margins are relatively longer; Fig. 3A–C (vs. supraorbital and anterolateral margins shorter in V.pygmaeus; Takeda, 1977a: fig. 5A); the hepatic region and surfaces behind the anterolateral teeth are not swollen, at most with a few granules; Fig. 3A–C (vs. hepatic region with a prominent swelling posterior to the first anterolateral tooth in V. pygmaeus; Takeda, 1977a: fig. 5A); and the G1 is more slender and sinuous with the distal part proportionately longer and more distinctly tapering; Fig. 3H, I (vs. stouter and less sinuous with the distal part shorter in V. pygmaeus; Takeda, 1977a: fig. 5B, C).

The specimen from Singapore reported as “ Planopilumnus penicillatus ” by Balss (1938: 60) and “ Vellumnus penicillatus ” by Ng (2010: 51) is not this species. This specimen was re-examined. It appears to be a male in poor condition, being damaged and extremely soft with all the appendages detached. It seems to be a young V. labyrinthicus . As such, V. penicillatus s. str. remains restricted to Hong Kong.