The disc is saucer-shaped with an undulating margin and there are up to 200 tentacles arranged irregularly, often arching over the edge.

This may be used, as it is in some other sea anemone species, to prevent competing organisms from settling and occupying space nearby.

When it is disturbed, a large number of white threads known as acontia are discharged from cells on the column [2] and from the mouth.

[4] In the Netherlands the population fluctuates widely, with decreases occurring after severe winters with cold sea temperatures.

Other organisms found in the same habitat include the breadcrumb sponge, Halichondria panicea[5] and the soft coral, Alcyonium digitatum.

This causes a burning and itching sensation followed by erythema and blisters, the symptoms of "sponge fishermen's disease".