Halimeda tuna (Ellis & Solander) Lamouroux

    Thalli erect, single, light to dark-green, moderately to lightly calcified; 5-10 cm long. Thalli sparse to dense, dichotomously to trichotomously branched. Thallus attached by single, small holdfast. Basal segments strongly calcified, subcuneate to subcylindrical, remaining segments discoid to subcuneate, with a rough surface, 14-20 mm wide and 8-13 mm long. Internal structure shows two distinct regions, cortex with three to four layers of utricle, Primary utricles lightly coalescent after decalcification; polygonal in outline in surface view, with cell walls thicker than the other species, 44-55 µm in diameter (surface view) and 95-166 µm long in cross section. Every secondary utricle supports 6 or more primary utricle; secondary utricles 37-48 µm wide and 111 - 17 µm long. Medullary siphons interwoven, with extensive or short nodal fusions in groups of 2-3.