Hyastenus cracentis Griffin & Tranter, 1986

(Fig. 2A–D)

Hyastenus diacanthus.— Griffin & Tranter 1974: 170 [Not Pisa (Naxia) diacantha De Haan, 1839].

Hyastenus cracentis Griffin & Tranter, 1986: 125 (identification key), 138, figs. 44, 47c, d (type locality: Java Sea, Gasper Straits).— Loh & Ng 1999: 64, fig. 4.— Ng et al. 2008: 103 [list].— Windsor & Ahyong 2013: 726 (identification key).

Material examined. 1 juvenile male (2.2 × 2.8 mm) (NIO /BOD/AB/BRY/00001), RVSS 1, west of Vijaydurg, Arabian Sea, 16.45°N, 72.08°E, 27 m depth, Van Veen grab, coll. R. Periasamy, 5 January 2014.

Diagnosis. Carapace pyriform, longer than wide. Rostrum almost as long as post-rostral CL; rostral spines slender, horizontal, separate from near base, lacking accessory spine (Fig. 2A). Dorsal carapace smooth; protogastric, mesogastric, cardiac and anterior branchial regions lacking tubercles; short epibranchial spine present (Fig. 2A). Orbits reduced, with narrow supraorbital eave (produced into weak, horizontal preorbital spine), a cupped postorbital process; upper orbital hiatus keyhole-shaped (Fig. 2B). Basal antennal article narrow anteriorly or sub-rectangular, almost as broad as long, anterolateral spine separated from flagellar base by notch (indicated by arrowhead in Fig. 2C), proximal portion of lateral margin produced into convex lobe. Maxilliped 3 merus triangular, as long as wide, length 0.5 × ischial length (Fig. 2D). Pterygostomian margin with 2 tubercles. Cheliped slender, dactylus short, curved; propodus sub-cylindrical, merus with 5 or 6 spines on posterior margin (Fig. 2A). Pereopods 2–5 dactyli bearing row of ventral spines (Fig. 2A).

Colouration. Fresh specimen: mottled red, chelae greyish (Fig. 2A). Preserved specimen: light red (Fig. 2B).

Biology. Known to inhabit sandy substrates; 28–52 m (Griffin & Tranter 1974, 1986). The present specimen was collected from sandy substrate, at 27 m depth, covered with macroalgae.

Remarks. Griffin & Tranter (1986) described H. cracentis from a male from Gaspar Strait, Indonesia. This species closely resembles H. bispinosus Buitentijk, 1939, H. inermis (Rathbun, 1911) and H. minutus Buitentijk, 1939 in the absence of ornamentation on the mesogastric and anterior brachial regions of the carapace, a relatively broad upper orbital hiatus, and the presence of a sharp spine on the anterolateral angle of the basal antennal article. However, H. cracentis differs from H. bispinosus in having the preorbital and antorbital angles equally produced laterally (vs. distinct preorbital angle of eave in the latter species), and from H. inermis and H. minutus in relatively longer rostral spines> two-thirds post-rostral carapace length (vs. only half or less in the latter two species). The Indian specimen largely conforms to the description of the holotype (Griffin & Tranter 1986) in the elongated rostrum (> two-thirds of carapace length) keyhole-shaped upper orbital hiatus, absence of mesogastric tubercle on the carapace; and the anterolateral angle of basal antennal article produced forwards and slightly outwards as a short spine. On the other hand, the present specimen of H. cracentis differs from the holotype in the absence of a tubercle on the hepatic region of the carapace.

Geographical distribution. Red Sea, Bay of Bengal (India), Java (Indonesia) (Griffin & Tranter 1986); Hong Kong (Loh & Ng 1999); eastern Arabian Sea off India (present study).