Size up to about 70 mm across the base with a tentacle span of up to 180 mm. Base lightly but closely adherent, broader than column.
Column variable in height, often short and hidden by the tentacles but capable of becoming taller than wide; smooth, with small, roughly conical acrorhagi on the parapet.
Tentacles: Tentacles long, fairly stout and flexuous, irregularly arranged in correlation with habitual reproduction by longitudinal fission, up to about 200 in number. The tentacles are rarely retracted but they can be completely retracted into the column (A. viridis tentacles).
Colouration: Column reddish or greyish brown, usually darkest above, sometimes with irregular pale streaks, acrorhagi matching the ground colour. Disc brown or greyish, usually with white radial lines, tentacles grey-brown or bright grass-green with purple tips. Some tentacles may bear a median longitudinal pale line, more rarely they are suffused with crimson, mainly on the aboral sides, which may extend onto the column. Occasionally pale specimens - whitish or yellowish - may occur.
In pools, attached to rocks or various algae, on Zostera leaves etc., usually in well-lit situations. Occurs mainly on the shore, from about mid-tide level downwards, mostly in localities exposed to strong wave action but also in sheltered places, and in the shallow sublittoral down to about 20 m. A conspicuous species and, if present, may well be the first anemone to catch the eye.
A. viridis is unable to tolerate prolonged conditions of extreme cold; in the exceptionally cold winter of 1963-64 it disappeared from many localities.
Locally abundant on south and west coasts of the British Isles, extending north to mid-Scotland. Common on all south-west coasts of Europe and in the Mediterranean.
The common name "snakelocked anemone" or "snakelocks" was first applied by Gosse to another species, Sagartiogeton undatus, but has been taken over by popular usage for the present species.