The genus Cellaria includes three British species. Colonies consist of rigidly calcified branch segments, connected by very apparent narrow, chitinous flexible nodes at regularly spaced bifurcation points. The branches increase by dichotomously to form erect tufts. Occasionally a flexible node gives rise to only one descendant branch rather than two branches. Colonies are typically white.
Autozooids are lozenge-shaped or hexagonal, arranged in alternating longitudinal series around the whole branch. The opesia is barely larger than the operculum, semicircular, with a raised border proximally and two condyles laterally. Colonies are anchored by a bundle of chitinous, tubular rootlets.
Cellaria species are able to colonise a variety of substrates including shells, stones and coarse sediment in subtidal waters.
To identify the British species it is necessary to recognise “true hexagonal” areolation – the disposition of the longitudinal series of autozooids relative to each other – shown by Cellaria salicornioides as opposed to the “rhomboid” areolation present in the other two species.