Urnalana angulata ( Rathbun, 1911 )

Padate, Vinay P., Cubelio, Sherine Sonia & Takeda, Masatsune, 2024, First records of some coral reef-associated brachyuran crabs from the Nicobar archipelago, India, Zootaxa 5486 (4), pp. 476-498 : 481-483

Urnalana angulata ( Rathbun, 1911)

( Figs. 2B , 4A–G )

Leucosides angulata Rathbun, 1911: 202 , pl. 15, fig. 8 [type locality: Seychelles, 31 fathoms (= 57 m) depth).

Leucosia angulata — Ihle 1918: 315 (index).— Serène 1968: 47.— Ovaere 1987: 197, figs. 3a, 6b.

Urnalana angulata — Galil 2005: 13, figs. 1A, 4A.— Ng et al. 2008: 95 (list).

Not Leucosia angulata — Tyndale-Biscoe & George 1962: 77, pl. 1 fig. 3, pl. 2 fig. 3.—Davie 2002: 263. [= U. cumingii (White, 1847) , fide Galil 2005]

Material examined. 1 juvenile (6.9 × 7.0 mm) (IO/SS/BRC/00184), FORVSS stn. 38818, south of Great Nicobar Island , Nicobars, India, 6.65°N, 93.83°E, 56 m depth, chain bag dredge, coll. V.P. Padate, 16 August 2019 .

Description. Carapace subpentagonal, slightly wider than long, regions indistinct; frontal margin projecting, bilobate; anterolateral margin angular, projecting ventrally; posterolateral margins setose; thoracic sinus with large, lozenge-shaped granule ventrally ( Figs. 2B , 4A ).

Antennule folding obliquely; antenna short, inserted between antennular fossa and orbit ( Fig. 4B, C ); buccal cavity subtriangular ( Fig. 4C ); mxp3 merus subequal in length to ischium, elongate triangular; exopod laciniate ( Fig. 4D ).

Chelipeds subequal, merus less than half as long as carapace, widened distally; anterior margin bearing row of 9 granules, including 3 large granules medially, posterior margin bearing 9 close-set smaller granules, splitting into two divergent rows distally; dorsal surface on distal half, proximal half with a cluster of 3–4 granules covered by dense tomentum ( Fig. 4E, F ); carpus outer margin carinate; palm slightly wider than long, with carinate margins; fingers carinate, slightly longer than palm. Pereopods 2–3 missing, P4 merus with 1 row of granules on posterior margin ( Fig. 4G ); carpus dorsally carinate, propodi dorsally and ventrally carinate.

Pleon subtriangular ( Fig. 4B ).

Colouration. Fresh specimen: Carapace bright orange on anterior three-fourths bearing lighter streaks, whitish posteriorly, Chelipeds whitish, with orange specks on outer margin of merus, both margins of palm and midlength of fingers ( Fig. 2B ).

Biology. The present specimen was collected from rocky substrate in the vicinity of crinoids, at 56 m depth. Known to occur on coarse sand and sandy mud substrates ( Ovaere 1987) in coral reefs at 40–57 m depths ( Galil 2005).

Remarks. Rathbun (1911) described Leucosides angulata from a male collected from the Seychelles. Ovaere (1987) reported this species from Papua New Guinea. Galil (2005) transferred this species to Urnalana Galil, 2005 owing to an urn-shaped carapace with pubescence on posterolateral margins, epimeral ledge visible in dorsal view, a pubescent patch proximally on the upper and the lower surfaces of cheliped merus, and an uncoiled shaft of G1. According to Galil (2005), Urnalana angulata differs from its closest congener U. cumingii (Bell, 1855) in having a bilobate frontal margin ( Fig. 4A ) (versus sinuous margin with shallow median depression in U. cumingii ; see Galil 2005: fig. 1C); and the large granule anteriorly in the thoracic sinus (fig. 4B) (versus small granules in U. cumingii ; see Tan 1996: fig. 5a). The Indian specimen conforms to the description of the holotype ( Rathbun 1911) in the distinctly angular hepatic margin, a bilobate frontal margin and the presence of a row of flattened tubercles on the anterior margin of cheliped merus. However, it differs from the description of the holotype in the cheliped palm being slightly wider than long and dactyli subequal to palm in length ( Fig. 4E, F ) (versus palm slightly longer than wide and dactyli slightly longer than palm; Rathbun 1911: pl. 15 fig. 8).

Geographical distribution. Seychelles, Mauritius, Sri Lanka, Papua New Guinea ( Galil 2005). The present observation is the first record from Indian waters.

Figures

FIGURE 2. Dorsal habitus photographs (A–C, E–G: fresh specimens; D: ethanol-preserved specimen): (A) Singhaplax ockelmanni (Serène, 1971), male (IO/SS/BRC/00360, 4.8 × 2.5 mm); (B) Urnalana angulata (Rathbun, 1911), undetermined sex (IO/SS/BRC/00184, 6.9 × 7.0 mm); (C) Pseudolambrus confragosus (Calman, 1900), male (IO/SS/BRC/00323, 22.2 × 18.0 mm; (D) Cavoportunus dubius (Laurie, 1906), male (IO/SS/BRC/00191, 26.9 × 20.4 mm); (E) Cyrtocarcinus truncatus (Rathbun, 1906), male (IO/SS/BRC/00193, 8.6 × 6.1 mm); (F) Visayax osteodictyon Mendoza & Ng, 2008, male (IO/SS/ BRC/00194, 5.2 × 3.6 mm); (G) Xanthias joanneae Mendoza, 2013, male (IO/SS/BRC/00197, 6.4 × 4.2 mm). Scale bars: A–B, E, G, 2 mm, C, 10 mm, D, F, 5 mm.

FIGURE 4. Urnalana angulata (Rathbun, 1911), undetermined sex (6.9 × 7.0 mm) (IO/SS/BRC/00184), Andaman Sea, India: (A) carapace, dorsal view; (B) carapace, ventral view; (C) carapace, frontal view; (D) left mxp3, ventral view; (E) right cheliped, dorsal view; (F) right cheliped, ventral view; (G) P4, dorsal view. Scale bars: A–B, E–F, 2 mm, C–D, G, 0.5 mm.