Antedon petasus

(Düben and Koren, 1846)

Body cup-shaped with ten feathery arms, arm length is typically 70-100 mm, sometimes over 100 mm. The arms are either brown or red and white with the colour often in large patches. Fifty to 100 cirri arising around a low hemispherical plate. The lower side of the arms has an almost smooth outline.
The distal edges of arm ossicles (brachials) are prominent. The proximal 6-7 joints of the genital pinnules with rather prominent spines at the distal outer corner; beyond these, the pinnule joints diminish rapidly in size. The genital organ is confined to the basal half of the pinnule as in Antedon bifida (A. bifida arm).

This is a free-moving species of sheltered habitats, which is often also found temporarily attached by clawed cirri to a wide range of objects, such as rocks, kelp, (sessile) animals or directly to wrecks or boulders.

Northern parts of the North Sea, along the British and Skandinavian coasts in shallow waters, also around Shetland.
Antedon petasus replaces A. bifida in the north and in deeper waters.