References: Taylor, 1960: 261, pl. 36, figure 5; Jaasund, 1976: 47, figure 96; Tseng, 1984: 186, pl. 94, figure 2; Womersley, 1987: 300, figures 109A, 110A, B; Coppejans et al., 1995b: 178, figure 1; Cribb, 1996: 49, figure p. 48; Lewmanomont and Ogawa, 1995: 73; Littler and Littler, 2000: 248, figure p. 249; Payri et al., 2000: 144, figure p. 145; Skelton and South, 2002: 158, figure 19A; Littler and Littler, 2003: 178, top figure p. 179.
Type locality. Uncertain.
Vouchers. HEC 14675 azb (zF), 20 September 2001, Rivière Banane (s.s. 12); HEC 14756 a, 22 September 2001, Grand Baie (s.s. 11); HEC 14786, 25 September 2001, Passe Grand Bassin (s.s. 1).
Ecology. Epilithic, from high intertidal (rare) down to spring low water mark (more frequent).
Distribution. Aldabra Islands, Andaman Islands, Australia, Bahrain, Bangladesh, Diego Garcia Atoll, India, Indonesia, Kenya, Kuwait, Laccadives, Malaysia, Maldives, Mauritius (Børgesen, 1941: 62, 1948: 49–50), Mozambique, Nicobar Islands, Pakistan, Réunion (Montagne and Millardet, 1862: 21 ~ Hydroclathrus cancellatus Bory de Saint-Vincent), Rodrigues (Dickie, 1877a: 6), Saudi Arabia, Seychelles, Singapore, Somalia, South Africa, Sri Lanka, Tanzania.
Note. The crisp, three-dimensional thalli of H. clathratus mainly grow epilithic at about low water mark. The suppler, strap-like thalli of H. tenuis were usually entangled with other seaweeds (e.g. Sargassum) or corals, although it has also been found drifting in the lagoon. In a few instances, we observed that H. clathratus, exposed at low tide to the air, was closely associated with thalli of H. tenuis, continuously submerged in the rock pool next to it. This casts doubt on the taxonomic identity of H. tenuis. Womersley (1987: 302) states that ‘ H. clathratus is distinctive in form but varies considerably in compactness of the net, the more compact forms usually occurring in shallow water with more wave action’. He does not refer to H. tenuis.