Halimeda opuntia (Linnaeus) Lamouroux 1816

    Thalli strongly calcified, white-green with thick prostrate clumps, 9- 20 cm in long, attaching to substratum by multiple felt-like holdfasts. Branching dense, polystichous and overlapping. Segments variable in shape, usually trilobate, flattened to cylindrical, sometimes twisted, auriculated to crenulated 12-18 mm in wide and 6-9 mm long; Distal margin slightly to deeply lobed. Internal structures of the segments show distinct cortex and medulla regions. Cortex composed of 3-5 layers of utricles, dichotomously branched; primary utricles rounded to polygonal, 17-42 µm in diameter. Secondary utricle elongated 58-70 µm long and every utricle supports 2 primary ones. Medulla siphons long, interwoven, fused in pairs, rarely in groups of 3-4, with short nodal fusions.