First records of some coral reef-associated brachyuran crabs from the Nicobar archipelago, India Author Padate, Vinay P. Centre for Marine Living Resources & Ecology, Ministry of Earth Sciences, Government of India, Atal Bhavan, LNG Terminus Road, Puthuvype, Kochi, 682508, India. Author Cubelio, Sherine Sonia Centre for Marine Living Resources & Ecology, Ministry of Earth Sciences, Government of India, Atal Bhavan, LNG Terminus Road, Puthuvype, Kochi, 682508, India. Author Takeda, Masatsune Department of Zoology, National Museum of Nature and Science, Tokyo. 4 - 1 - 1 Amakubo, Tsukuba, Ibaraki 305 - 0005, Japan. text Zootaxa 2024 2024-07-29 5486 4 476 498 http://dx.doi.org/10.11646/zootaxa.5486.4.2 journal article 10.11646/zootaxa.5486.4.2 1175-5326 13210270 29F6FDC3-3166-4309-A7B2-1582358AA1FD Cavoportunus dubius ( Laurie, 1906 ) ( Figs. 2D , 6A–G , 10I–L ) Neptunus ( Achelous ) dubia Laurie 1906: 416 , fig. 9 ( type locality: Gulf of Mannar , Sri Lanka ). Portunus ( Achelous ) dubius — Stephenson & Rees 1967: 4 (list) 20, fig 3a–b, pl. 2A.— Stephenson 1972a: 15 , 38.— Stephenson 1972b: 135 .— Stephenson 1976: 16 .— Moosa 1981: 143 (list), 147.— Crosnier 1984: 401 .— Crosnier 1985: 33 , figs. 1a– e.— Zarenkov 1994: 115 .— Moosa 1996: 521 .— Poupin 1996: 31 .— Neumann & Spiridonov 1999: 19 .— Crosnier 2002: 404 .— Ng et al . 2008: 151 (list). Portunus ( Cycloachelous ) yoronensis Sakai, 1974: 90 .— Sakai 1976: 349 , figs. 189a–d.— Ng et al. 2008: 151 (list). Cavoportunus dubius — Nguyen & Ng 2010: 41 , figs. 1–4.— Komatsu 2011: 257 , fig. 19C.—Mantellato et al . 2018: 192, 194, fig. 1. Material examined. 1 male (26.9 × 20.4 mm ) (IO/SS/BRC/00191), FORVSS stn. 38811, west of Tillangchong Island , Nicobars , India , 8.44°N , 93.59°E , 69 m depth , chain bag dredge, coll. V.P. Padate , 13 August 2019 . Description. Carapace hexagonal, 1.3 times as wide as long, dorsal surface glabrous; dorsal surface microscopically granular with distinct regions, bearing scattered granules; only metagastric ridge distinct, other ridges indistinct ( Figs. 2D , 6A ). Frontal margin with 4 teeth, projecting beyond tip of internal supraorbital angle; orbits relatively large, moderately dorsally inclined, supraorbital margin with single fissure, inner supraorbital margin rounded; infraorbital margin straight, granular, with forward-directed tooth; anterolateral margin with 9 teeth, first tooth largest, second to ninth teeth smaller; posterolateral junction of carapace rounded ( Fig. 6A ). FIGURE 6 . Cavoportunus dubius ( Laurie, 1906 ) , male (IO/SS/BRC/00191, 26.9 × 20.4 mm), Andaman Sea, India: (A) carapace, dorsal view; (B) carapace, frontal view; (C) right mxp3, ventral view; (D) left chela and carpus, lateral view; (E) left chela and carpus, dorsal view; (F) left P5, dorsal view; (G) male pleon and telson, ventral view. Scale bars: A, 5 mm, B–G, 2 mm. Antennule folding obliquely; basal antennal article with lobe-like process, flagellum lodged in orbital hiatus ( Fig. 6B ); epistome triangular, anterior and posterior margins elevated. Buccal cavity subquadrate; mxp3 merus subquadrate, shorter than ischium, anterolateral margin produced into rounded lobe ( Fig. 6C ). Cheliped 1.8 times as long as CL, merus with 4 spines on anterior margin, 1 distal spine on posterior margin ( Fig. 2D ); carpus with long spine on inner angle; palm with 2 granular ridges on dorsal surface terminating in subdistal spines, short spine at carpal articulation, outer surface with 3 longitudinal granular costae on lower half; fingers slender, gently curved, as long as palm ( Fig. 6D, E ). Pereopods 2–4 dactyli longer than propodi ( Fig. 2D ); P5 merus posterior margin dentate, other segments unarmed ( Fig. 6F ). Male pleon triangular, somite 3 posterior margin with median cleft, somite 4 lateral margins convex, those of somite 5 slightly convex; telson small, triangular, 0.8 times as long as wide ( Fig. 6G ). G1 stout, S-shaped; basal part relatively slender, subdistal portion distinctly dilated into a bluntly triangular lobe; distal tip with distinct folds ( Fig. 10I–K ); G2 slender, tapering, 0.6 times as long as G1 ( Fig. 10L ). Colouration. Fresh specimen: Carapace white with densely-packed reddish reticulate markings on the dorsal surface, particularly the granules, granulated ridges and anterolateral spine tips ( Fig. 2D ). Posterolateral carapace junction, edges of first two pleonites, outer carpal spine, outer carina and dorsal spine of the cheliped palm and dorsal surface of cheliped dactylus with silvery iridescence ( Fig. 2D ). Biology. The present specimens were collected along with gorgonians and sponges from coral reef habitat at 69 m depth. Known to inhabit coral reefs ( Nguyen & Ng 2010 ), on fine coral sand ( Stephenson and Rees 1967 ) at depths from 20–500 m ( Nguyen & Ng 2010 ). Remarks. Cavoportunus dubius was originally described by Laurie (1906) from two males collected from the Gulf of Mannar and off Negombo, Sri Lanka . Stephenson & Rees (1967) reported Portunus dubius from the Philippines . Subsequently, Sakai (1974) described Portunus yoronensis from a male collected from Yoron Island, Japan . Crosnier (1984) and Nguyen & Ng (2010) synonymized Portunus ( Cycloachelous ) yoronensis Sakai, 1974 with Neptunus ( Achelous ) dubia Laurie, 1906 . Further, Nguyen & Ng (2010) transferred this species to a new genus, Cavoportunus , owing to the presence of two distinct depressions lateral to the sternal medial groove on the male sternum to accommodate a distinct G1 (with a swollen and bilobed subdistal part). The present specimen conforms to the morphology of the male pleon, third maxillipeds, left cheliped and G1 depicted by Laurie (1906 : fig. 9). However, the carapace of the Indian specimen possesses densely packed fine reddish orange reticulation on the carapace ( Fig. 2D ), as compared to reddish spots scattered on a white background in the Japanese specimen reported by Nguyen & Ng (2010 : fig. 1). Geographical distribution. Sri Lanka , Philippines , Japan , and French Polynesia ( Nguyen & Ng 2010 ). The present observation is the first record for Indian waters.