Vellumnus intonsus, Ng & Prema & Ravichandran, 2024

Ng, Peter K. L., Prema, Mani & Ravichandran, Samuthirapandian, 2024, Descriptions of new and rare crabs associated with coral rubble and sponges from Kanyakumari, southeastern Arabian Sea, southern India (Decapoda: Brachyura: Epialtidae and Pilumnidae), Zootaxa 5476 (1), pp. 325-341 : 335-339

Vellumnus intonsus n. sp.

( Figs. 8–10 )

Pilumnus labyrinthicus .— Henderson, 1893: 365 (Gulf of Manaar); Kathirvel & Gokul, 2010: 27. (Not Pilumnus labyrinthicus Miers 1884 ).

Vellumnus labyrinthicus .— Trivedi et al. 2018: 61 (list).

Type material. Holotype: male (cw 4.3 mm, cl 3.0 mm), CASAU-CR-2021-1024, in coral rubble, Mankudy fish landing centre, Kanyakumari district, Tamil Nadu, southern India, Southeastern Arabian Sea, 8°05′29.8′′N, 77°29′02.9′′E, 50–60 m, coll. M. Prema, 5 November 2021 . Paratype: 1 ovigerous female (cw 4.3 mm, cl 3.1 mm), ZRC 2022.0999 , same data as holotype .

Etymology. The name is derived from the Latin for bearded and unshaven; alluding to the appearance of the species.

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 and cardiac regions ( Fig. 8A, B ); epigastric, mesogastric, postorbital cristae low, gastric and subhepatic regions with scattered low granules, hepatic region with low broad tubercle, may be very low ( Figs. 8C, D , 10A, B ); frontal margin distinctly convex, lateral lobule sharp, distinct, separated from frontal lobes by deep V-shaped cleft; supraorbital margin with median fissure, margin convex ( Figs. 8C, D , 10A, B ); external orbital tooth triangular, first anterolateral tooth triangular, third tooth smallest; subhepatic tooth low or distinct, may be visible in dorsal view ( Figs. 8C, D , 10A, B ); surface of merus of third maxilliped smooth, anteroexternal angle of rounded, not auriculiform, ischium relatively short ( Fig. 10C ); outer surface of chelae with numerous relatively large round granules, vaguely arranged in longitudinal rows, carpus with numerous round granules, without distinct tooth on inner angle, fingers shorter than palm ( Fig. 9B–E ); ambulatory legs without distinct crests or ridges, unarmed; surfaces completely obscured by numerous long, short setae ( Fig. 9F ); anterior thoracic sternum with surfaces relatively smooth, suture between sternites 3 and 4 shallow, medially interrupted ( Fig. 9A ); male pleon relatively narrow, subrectangular, pleonal somites 1, 3 subequal in width; telson semicircular ( Figs. 9A , 10F ); G1 slender, sinuous along entire length, distal part gently bent laterally with sharp tip ( Fig. 10G, H ).

Variation. In the holotype male, there is a distinct large but low tubercle behind the first anterolateral tooth and the subhepatic region has a distinct tooth which is clearly visible in dorsal view ( Figs. 8D , 10A ). In the paratype female, however, the surface behind the first anterolateral tooth is only slightly raised and barely visible and the subhepatic tooth is low and poorly developed, and hardly visible in dorsal view ( Figs. 8C , 10B ). The two specimens, however, agree in all other aspects and we are confident they are conspecific.

Colouration. Not known.

Remarks. Henderson (1893: 365–366) recorded one small specimen cw 5.0 by cl 4.0 mm in size (no sex indicated) as “ Pilumnus labyrinthicus ” from Rameswaram, southern India, noting that it has “the very characteristic markings or lines on its dorsal surface, which hear some resemblance to a face.” Kathirvel & Gokul (2010) subsequently listed the species based on this record from the Gulf of Mannar. On the basis of this description and distribution, this record is likely to be conspecific with V. intonsus n. sp. The records of “ Pilumnus labyrinthicus ” from the Andaman and Nicobar Islands by Dev Roy & Nandi (2012) and Dev Roy (2015) need to be clarified and their specimens examined to confirm if they are V. labyrinthicus s. str. or V. intonsus n. sp.

The small adult size (cw less than 8 mm), less obvious setal pattern on the carapace, the absence of ridges under the vermiform setal patterns, and relatively wider male thoracic sternum and male pleon allies V. intonsus n. sp. most closely with V. penicillatus (type locality Hong Kong). Vellumnus intonsus n. sp. can be separated from by the lateral lobule of the front being separated from the frontal lobes by a deep cleft ( Fig. 10A, B ) (vs. separated by a shallow concavity in V. penicillatus ; Ng & Clark 2023: fig. 3A–C); the external orbital tooth is triangular in shape ( Fig. 10A, B ) (vs. truncatiform in V. penicillatus ; Ng & Clark 2023: fig. 3A–C); the granules on the cheliped carpus and chela are proportionately larger and fewer in number ( Fig. 9B–E ) (vs. smaller and more numerous in V. penicillatus ; Ng & Clark 2023: figs. 1A, B, 2A, B); and the distal part of the G1 is distinctly curved downwards and hooked ( Fig. 10G, H ) (vs. distal part is curved laterally at approximately right angles in V. penicillatus ; Ng & Clark 2023: fig. 3H, I).

Vellumnus intonsus n. sp. also resembles V. pygmaeus (type locality Ogasawara Islands) and V. pictus (known only from one female from the Persian Gulf) and most of the differences between them are shared with V. penicillatus . Vellumnus pygmaeus can be separated as it has the supraorbital margin prominently more convex ( Takeda, 1977: fig. 5A) (vs. supraorbital margin gently convex with median fissure in V. intonsus n. sp.; Fig. 8C, D , 10A, B ); and the G1 is relatively stouter with the distal part curved laterally ( Takeda, 1977: fig. 5B, C) (vs. G1 slender, sinuous with the distal part gently bent laterally, with a sharp tip in V. intonsus n. sp.; Fig. 10G, H ). Compared with V. pictus , V. intonsus n. sp. also has the merus of the third maxilliped smooth with the anterolateral angle gently rounded ( Fig. 10C ) (vs. surface with granules and the anterolateral angle is auriculiform in V. pictus ; Fahimi & Naderloo, 2023: fig. 1D); and there are relatively more numerous granules on the outer surface of the chela ( Fig. 9B–E ) (vs. fewer and less evenly distributed in V. pictus ; Fahimi & Naderloo, 2023: fig. 1C).

Vellumnus intonsus n. sp. also differs from the type species, V. labyrinthicus , in the vermiform setal pattern being only evident on the gastric and cardiac regions and when denuded, the underlying surface is smooth ( Fig. 8A–D ) (vermiform pattern more pronounced in V. labyrinthicus with the setae is present on most of the carapace regions, and there is an ridge under these setae when denuded; Ng 2010: figs. 13A, 14A, 15A); the anterolateral teeth are relatively shorter with the last tooth directed obliquely anteriorly ( Fig. 8C, D ) (anterolateral teeth stronger and longer with the last tooth directed laterally in V. labyrinthicus ; Ng 2010: fig. 14A); the male anterior thoracic sternum is proportionately wider ( Fig. 9A ) (proportionately narrower in V. labyrinthicus ; Ng 2010: fig. 14B); the male pleon is relatively wider, especially across somites 3 and 4 ( Fig. 10F ) (entire pleon distinctly narrower in V. labyrinthicus ; Ng 2010: fig. 16D); and the G1 is more distinctly sinuous with the proximal half strongly curved ( Fig. 10G, H ) (the proximal half is only gently curved with the G1 relatively less sinuous in V. labyrinthicus ; Ng 2010: figs. 15C, 16E, F).

Vellumnus intonsus n. sp. can be separated from V. minabensis and V. tki by its proportionately wider male anterior thoracic sternum ( Fig. 9A ) (vs. anterior thoracic sternum proportionately narrower in V. minabensis and V. tki , e.g., Ng & Clark 2023: fig. 6E); the median lobe of the posterior margin of the epistome is distinctly triangular in shape ( Fig. 10D ) (vs. median lobe is lower and more lobiform in V. minabensis and V. tki , e.g., Ng & Clark 2023: fig. 6B); the ischium of the third maxilliped is relatively shorter ( Fig. 10C ) (vs. ischium distinctly longer in V. minabensis and V. tki , e.g., Ng & Clark 2023: fig. 6C); there are fewer but larger granules on the outer surface of the cheliped ( Fig. 9B–E ) (vs. more numerous smaller granules in V. minabensis and V. tki , e.g., Ng & Clark 2023: fig. 5B, C); and the distal part of the G1 is distinctly more elongate ( Fig. 10G, H ) (vs. G1 distal part shorter in V. minabensis and V. tki , e.g., Ng & Clark 2023: fig. 6H, I).

Distribution. Only known from the type locality.

Figures

FIGURE 8. Vellumnus intonsus n. sp., holotype male (cw 4.3 mm, cl 3.0 mm) (CASAU-CR-2021-1024), India: (A, B) overall habitus (carapace gently brushed with right side denuded); (C, D) right side of carapace (denuded); (E) frontal view of cephalothorax; (F) antennules, antenna, orbit and epistome; (B, D) paratype ovigerous female (cw 4.3 mm, cl 3.1 mm) (ZRC 2022.0999), India.

FIGURE 9. Vellumnus intonsus n. sp., holotype male (cw 4.3 mm, cl 3.0 mm) (CASAU-CR-2021-1024), India: (A) anterior thoracic sternum and pleon; (B) dorsal view of left cheliped; (C) dorsal view of right cheliped; (D) outer view of left chela; (E) outer view of right chela; (F) left P5. B, C, and D, E, photographed to same magnification.

FIGURE 10. Vellumnus intonsus n. sp., holotype male (cw 4.3 mm, cl 3.0 mm) (CASAU-CR-2021-1024), India: (A, B) right side of carapace (setae denuded); (C) left third maxilliped (denuded); (D) posterior margin of epistome; (E) left P5 dactylopropodal lock; (F) pleon; (G) left G1 (ventral view); (H) left G1 (dorsal view); (I) = left G2. Paratype ovigerous female (cw 4.3 mm, cl 3.1 mm) (ZRC 2022.0999), India. (I) right side of carapace (setae denuded); B) paratype ovigerous female (cw 4.3 mm, cl 3.1 mm) (ZRC 2022.0999), India. Scales: A–F = 0.5 mm; G–I = 0.1 mm.