Brankocleistostoma fossulum
Creators: name: Lasley Jr, Robert M.
name: Anker, Arthur
name: Naruse, Tohru
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Varunidae
Brankocleistostoma
Brankocleistostoma fossulum

description: Brankocleistostoma fossulum (Barnard, 1955)
(Figs. 5–8)
Paracleistostoma fossula Barnard, 1955: 24.
Brankocleistostoma fossulum.— Števčić 2011: 134; Ng 2012: 63.— Naruse 2015: 212.
Material examined. FLMNH UF 69027, 1 male (6.3/4.0), BOMAN-14541, Oman, Masirah west (channel-side) coast, between Ghab Beach and southern tip of island, stn MASA-33, 20.210314°N, 58.634534°E, near-shore sandflat with coarse and fine sand, depth 0.5–1 m, suction pump, coll. A. Anker & V.N. Peinemann, 18.11.2022; FLMNH UF 36973, 1 male (6.7/4.1), BDJRS-2612, Saudi Arabia, Farasan Islands, Tiger Head Island, 16.79097°N, 42.19865°E, subtidal sandflat between corals, depth 1–3 m, suction pump, coll. A. Anker et al., 11.03.2113; FLMNH UF 36972, 1 female (6.4/4.0), BDJRS-2611, same collection data as for previous specimen; FLMNH UF 36769, 1 female (8.1/4.9), BDJRS-2063, Saudi Arabia, Farasan Islands, Naf Shuma, 16.75273°N, 41.60488°E, subtidal sandflat between corals, depth 1–3 m, suction pump, coll. A. Anker et al., 09.03.2113; FLMNH UF 36767, 1 female (8.9/5.5), BDJRS-2060, same collection data as for previous specimen; FLMNH UF 36860, 1 male (cw/cl indet.), BDJRS-2317, same collection data as for previous specimen.
Diagnosis of male. Carapace (Fig. 5A) transversely rectangular; dorsal surface with 2 parallel transverse ridges, fading medially; anterolateral margin with 2 low, broad teeth. Mxp3 (Figs. 5B–C, 6C) forming broad median gape when closed; merus joining ischium obliquely; dactylus with numerous long setae reaching beyond base of merus to thoracic sternite 3. Chela each with subventral, longitudinal ridge; fingers gaping, with cutting edges bearing row of small teeth, cutting edge of dactylus armed with additional prominent tooth at mid-length. Thoracic sternum (Fig. 5C) wide; sternites 1 and 2 fused, granular, demarcated from sternite 3 by row of setae and granules; sternites 1–3 concave to accommodate setae of Mxp3; sterno-pleonal cavity reaching anterior margin of sternite 4, with anterior line of granules; sternal condyle on anterior margin of sternite 5 located at cavity margin. Penis sternal, appearing in sterno-pleonal concavity on sternite 8. Pleon (Figs. 5C, 6D) moderately wide; pleonite 1 divided by longitudinal ledge, distally raised; pleonite 2 very short; pleonite 3 wider than pleonite 2, of approximately same width as pleonite 1; pleonites 4–6 functionally fused, with sutures clearly demarcated; lateral margin of pleonite 6 convex, with socket for sternal condyle on inner surface. Telson (Figs. 5C, 6D) subtriangular, wider than long, with rounded distal margin. G1 (Fig. 6A, B) stout, subtriangular in cross-section, relatively straight but curving against sterno-pleonal cavity towards distal tip; base of chitinous distal beak emanating near rounded dorsal lobe; tip concave with anteroventral point, partially obscured by short, stiff, simple setae. G2 short, stout, with truncate tip.
Colour pattern. Somewhat variable. Carapace dorsal surface pale yellowish with more or less distinctive, brownish, red-brown or brown-grey-green marbling and small white chromatophores; post-cardiac area typically with small, oval- or butterfly-shape, dark brown or brown-red patch. Sternum whitish. Ocular peduncles without spots; cornea silvery with reddish line. Chelipeds and ambulatory legs pale or greyish with dark brown spots and blotches and patches of conspicuous white chromatophores sometimes forming transverse bands, especially on ambulatory legs; ventral side of legs without marked pattern (Figs. 7, 8; see also Ng 2012: fig. 2).
Distribution. Western Indian Ocean: Mozambique, Madagascar (Barnard 1955; Ng 2012), and Red Sea (Saudi Arabia) and Oman (Masirah Island) (present study).
Ecology. Madagascar: “ 5−15 m, sand and algae” (Ng 2012). Saudi Arabia and Oman: nearshore sandflats close to coral reefs, at depths between 0.5 m and 3 m; in burrows of unknown hosts (presumably symbiotic, but may also excavate own burrows).
Remarks. None of the males of B. fossulum from Saudi Arabia and Oman have two short, oblique ridges on each hepatic region of the carapace, as illustrated for the female from southern Madagascar by Ng (2012: fig. 3C). Similarly, Barnard (1955) did not observe, or at least did not illustrate, the two pairs of short hepatic ridges in the female holotype from Mozambique. The males in the present material seem to be intermediate in size (6.7/4.1 and 6.3/4.0 for two measured males) between Barnard’s (1955) female (5.0/3.3) and Ng’s (2012) female (8.1/4.6), and it is possible that these hepatic ridges may appear only after a certain size. However, since Ng’s (2012) specimen was collected in significantly deeper water (5−15 m vs 0.5−3 m) and in a region with known endemism, a molecular comparison of his female with the present material is desirable. The chelae are only slightly stouter and have more gaping fingers in males than in females (Fig. 5D, E; Barnard 1955: fig. 7d; Ng 2012: fig. 5D).
description: Published as part of Lasley Jr, Robert M., Anker, Arthur & Naruse, Tohru, 2024, Two new species and a new record of infaunal crabs (Decapoda: Brachyura: Pinnotheridae and Varunidae) from Oman and Saudi Arabia, pp. 207-229 in Zootaxa 5476 (1) on pages 215-218, DOI: 10.11646/zootaxa.5476.1.19, http://zenodo.org/record/12726911