Diadumene cincta

Stephenson, 1925

Diameter of base up to 10 mm, height to 35 mm; specimens twice this size have been recorded. A small delicate anemone, usually orange in colour; not infrequent on the shore and occurring on all coasts.
Base lightly or moderately adherent, a little wider than the column, often with an irregular outline due to basal laceration. Column elongated, cylindrical, almost vermiform in full extension; divided into scapus and a fairly long capitulum, with a parapet and shallow fosse. In full extension the fold of the parapet (and thus the fosse) smooths away completely, although scapus and capitulum remain reasonably distinct through differences in texture. Contraction of the column is characteristically jerky and often asymmetrical, resulting in a lop-sided appearance in the semi-contracted state. Cinclides irregularly scattered on the scapus, appearing as dark, slightly raised dots; acontia emitted fairly readily. Disc small, little wider than the column.
Tentacles: Tentacles slender, long in full extension, usually irregularly arranged but may be hexamerous, up to about 200.
Colouration: General colouration orange, in some specimens with a distinct greenish tinge. Scapus usually opaque, capitulum translucent with the mesenteric insertions forming opaque lines. Disc translucent, orange or colourless, sometimes greenish, occasionally with white markings. Tentacles translucent orange, sometimes with a pale bar at the base. Actinopharynx and lips deep orange, the former showing clearly through the capitulum. A pale buff form of this species is known from the Plymouth area, otherwise little variation occurs.
Reproduction: Basal laceration is habitual and frequent.
Nematocysts: p-mastigophores of acontia 41-60 x 6.0-8.0 µm, b-mastigophores of acontia 13-18 x 1.5-2.0 µm. Macrobasic p-mastigophores of tentacles 42-52 x 7.0-12 µm. This latter category of nematocyst is not known to occur in any other British anemone: as their occurrence appears to be invariable - no specimen has yet been examined which lacked them - they can be considered as characteristic of D. cincta in Britain.
Catch-tentacles: These occur commonly in some populations of this species, yet have never been observed in others. When present they are unmistakable due to their frosty opacity, stoutness in contraction - clearly thicker than normal tentacles, and their great length when extended - often exceeding the column.

Attached to any available hard substratum, particularly mussels or other bivalves. Occurs on the shore in pools and caves, not usually in places left dry at low water, and in the shallow sublittoral down to about 40 m. Tends to form very localized, often dense aggregations.

Recorded from many localities in the British Isles, on all coasts. Also known from Holland and the Atlantic coast of France; records from the Mediterranean may result from confusion with Metridium senile. May well be widely distributed throughout the north-east Atlantic.