Nematostella vectensis

Stephenson, 1935

This is a tiny anemone, the column rarely exceeding 15 mm in length and 1.5 mm diameter; exceptionally large specimens may attain 60 mm when fully extended.
Column elongated, the division between scapus and capitulum fairly distinct, that between scapus and physa less so. Scapus without nemathybomes or true periderm but a loose sheath of mucus and foreign material, which is easily removed, is usually present. Disc small, with a prominent hypostome.
Tentacles: Very long, the outer ones being longest; this species expands them freely even when not buried and in this state they usually exceed half the column length. Number of tentacles usually irregular due to asexual reproduction by transverse fission, 9-18, arranged in two approximately equal cycles; probably there would be 16 in a perfectly developed specimen but the commonest number is about 14. The nematosomes are visible through the transparent body wall as tiny opaque bodies; at rest they lie alongside the mesenteric insertions on the body wall but when the anemone becomes active they circulate freely within the coelenteron; their function is unknown (see Williams, 1979).
Colouration: The whole anemone is translucent and colourless except for a more or less well-developed pattern of opaque white on the column and disc, tentacles usually banded with white. These markings are variable in extent and occasionally absent altogether.

Occurs in isolated brackish lagoons, most localities having a substratum of shingle beneath a layer of fine mud. Normally the anemone burrows in the mud, often attaching to a stone by the rugae on its column; occasionally it is found attached to vegetation - Ruppia or Zostera - or may lie free on the mud surface. More rarely it occurs in tidal creeks or salt-marsh pools.

Recorded from several localities on the south and east coasts of England, not known elsewhere in Europe. In North America it has been found in California and in several localities in the east coast of USA and Canada.