Serenius ceylonicus (Laurie, 1906) (Fig. 5E–H) Zozymus gemmula var. ceylonica Laurie, 1906: 395, pl. 1, fig. 7 (type locality: Trincomalee, Ceylon). Zozymus gemmula ceylonica.— Sakai 1939: 450, pl. 89, fig. 2. Zosimus gemmula var. ceylonica.— Buitendijk 1960: 290. Zosimus gemmula ceylonica.— Guinot 1962a: 234, fig. 2 a–c. Serenius ceylonicus.— Guinot 1976: 276, fig. 46 d, pl. 17, fig. 7. Zosymus ceylonica.— Sakai 1976: 403, fig. 213.— Muraoka 1998: 38. Zosimus ceylonicus.— Miyake 1983: 104, pl. 35, fig. 4. Material examined. 2 males (4.6 × 3.2 mm, 5.9 × 4.1 mm) (NIO /BOD/AB/BRY/00003), RVSS 3, west of Vijaydurg, Arabian Sea, 16.48°N, 72.11°E, 28 m depth, Van Veen grab, coll. R. Periasamy, 6 January 2014. Diagnosis. Carapace sub-hexagonal, wider than long; regions, except 1L, clearly distinguished by shallow grooves, and lined with short tomentum on their anterior margins; frontal margin horizontal, bilobed; anterolateral margins with 4 flattened lobes behind external orbital angle, not separated by conspicuous grooves; (Fig. 5E). Maxilliped 3 merus with distal margin concave (Fig. 5F). Cheliped propodus tuberculate on outer and upper surfaces, largest tubercle on posterior proximal part flattened and projecting posteriorly inwards, all tubercles surrounded by short thick tomentum, fingers smooth, with acuminate distal tips (Fig. 5E, F, G). Pereopod 2–5 dactyli terminating in claw-shaped spine, propodus triangular; propodus and carpus with prominent ridges; carpus with transverse ridge on posterior surface. P4 merus serrated on upper surface (Fig. 5E, F, H). Colouration. Preserved specimen: carapace margins whitish, carapace regions 1F, 2F, 1M, inner 2M, 1L–5L, 1R, 2R, 1P and 2P brownish with darker tomentum on their anterior margins (Fig. 5E); cheliped fingers dark brown with white distal tips (Fig. 5F, G) Biology. Known to inhabit Pocillopora coral (Guinot 1962a). The present specimens were collected from rocky substratum, at 28 m depth, in the vicinity of corals and the sponge Phyllospongia sp. Remarks. Laurie (1906) described Zozymus gemmula var.ceylonica from 2males and 1 female from Trincomalee (Sri Lanka). He differentiated it from Z. gemmula De Man, 1852 (= Serenius gemmula (Dana, 1852)) on the basis of differences in the cheliped and pereopods 2–5. Buitendijk (1960) considered S. ceylonicus as a variety of Z. gemmula, distinguished from the latter in the presence of sharp-edged, flattened, and much less distinctly granular propodal tubercle on the cheliped projecting backwards and inwards. Guinot (1976) provided line illustrations of G1 and the dorsal view of the habitus to establish S. ceylonicus as a distinct species from S. gemmula. The Indian specimens conform to the type description of S. ceylonicus (Laurie 1906) (and differ from S. gemmula (Dana, 1852)) in the presence of a prominent posterior tubercle on the dorsal margin of the cheliped palm with its flattened surface and mesially projecting crest, the denticulated dorsal margins of the pereopod 2–5 meri, and the elevated dorsal crests of the pereopodal carpi and propodi forming a continuous line. Alcock (1898) reported its congener, Serenius pilosus (A. Milne Edwards, 1867) from the Angria Bank, Arabian Sea. The present specimens differ from S. pilosus in the carapace being less lobulated, with the lobes of the anterolateral margins not separated by distinct grooves (Buitendijk 1960). Geographical distribution. Gulf of Mannar off Sri Lanka, Japan, Maldives (Guinot 1976); eastern Arabian Sea off India (present study). The present observation is the first record from Indian waters indicating westward extension of the known geographical range.

Published as part of Padate, Vinay P., Periasamy, Rengaiyan, Rivonker, Chandrashekher U. & Ingole, Baban S., 2023, Coral reef-associated brachyuran fauna (Crustacea: Decapoda: Brachyura) from Angria Bank off the west coast of India, pp. 398-422 in Zootaxa 5357 (3) on page 409, DOI: 10.11646/zootaxa.5357.3.4, http://zenodo.org/record/10063288