Antedon petasus has a conical disc with five pairs of arms, each up to 10 cm (3.9 in) long and fringed with pinnules, giving it a feathery appearance.

[2][3] Antedon petasus is found on the coasts of north west Europe, the range extending from Scandinavia south to Britain.

[2] It can be found clinging to rocks and boulders, kelp and sessile invertebrates with its clawed cirri, preferring positions with a strong current.

[3] Antedon petasus is a suspension feeder, catching detritus and plankton with the tube feet on its pinnules.

Both male and female A. petasus liberate gametes into the water column from their genital organs situated at the base of certain specialised arms.