The Orange-striped anemone. Diameter of base up to 25 mm, height to 40 mm, but usually about half this size in British examples.
Base moderately adherent, usually a little wider than the column. Column divided into scapus and a long capitulum, with a parapet and fosse which are clearly defined and permanent in all states of expansion. Scapus tall in full extension, with inconspicuous cinclides on the endocoels; acontia fairly readily emitted. Capitulum up to half the length of the scapus in full extension, flaring out to the disc, which is wider than the parapet.
Tentacles: Long, very long in small specimens, hexamerous, or more usually, irregular in arrangement, up to about 100.
Colouration: Scapus olive green, brown or greyish, rarely pink; usually bearing prominent longitudinal stripes on the endocoels. The stripes may be orange, yellow or white, single or double; in some populations they are absent but such specimens are unknown in Britain. Capitulum and disc translucent grey-green, the latter often with white markings and occasionally with irregular blotches of reddish brown or crimson. Tentacles very translucent, colourless or pale grey-green, usually irregularly flecked with white or grey.
Reproduction: Longitudinal fission is habitual and frequent; after fission the regenerating part of the column is usually pink.
Nematocysts of acontia: Large p-mastigophores 29-48 x 5.0-6.0 öm, small p-mastigophores (amastigophores) 12-20 x 3.0-4.5 öm, b-mastigophores 12-21 x 2.0-3.0 öm.
In sheltered bays, harbours, or estuaries, rarely in the open sea; typically an intertidal species but may also occur in the shallow sublittoral. Attaches to any suitable hard substratum - rocks and stones, shellfish, wooden pilings and wharves, etc. Tolerant of extreme temperature and salinity variations, frequently occurring in brackish creeks or lagoons.
Reported from many localities in Britain, on all coasts; elsewhere widely distributed throughout Europe, including the Mediterranean, and the northern hemisphere in general.