Sarcodictyon roseum

(Philippi, 1842)

Stolon consisting of a flattened band up to 2.5 mm wide at the anthosteles, usually narrower between them, forming branching and anastomosing networks on the substratum. Often the stolon is laterally expanded to form a membranous encrustation by filling-in of gaps in the network. Polyps arise at irregular intervals along the stolon, tending to be more closely packed at the expansions. In contraction the anthosteles form low, rounded protruberances, usually with a few shallow radial grooves indicating the mesenteric insertions. Expanded anthocodia are about 6 mm tall with tentacles about 5 mm long.
Colouration: Typically the sclerites of the stolon and anthosteles are red or pink, occasionally yellowish or colourless. A thin layer of brownish, horn-like periderm covers this region, tending to darken the colour imparted by the sclerites. Expanded anthocodia are translucent white, their sclerites usually being colourless.
Sclerites: The densely packed sclerites of the anthosteles diminish fairly abruptly at the lower limit of the anthocodia, rarely forming triangular flaps between the mesenteric insertions. On the anthocodia the number of sclerites is variable: some are always present on the column, these usually being colourless but occasionally a ring of coloured ones occurs just below the tentacles.

Grows on rocks, stones, shells, etc; in some regions, e.g. the Mediterranean, this species may also occur on gorgonian axes. Occasionally found on the shore in shaded places but typically a sublittoral form occurring down to at least 100 m.

Common on all British coasts, occurring southward around south-west Europe to the Mediterranean, and northward to Scandinavia.