The delicately-branched tentacles of this species are usually seen emerging from mud. The body is soft and tapered at both ends, with a short tail. Tube-feet are scattered all over the body which is brown and may be covered in shell particles. The tentacles are normally plain brown in colour, paler or darker in different individuals. The spicules are found all over the body and consist of four-holed plates with central spires. 10-20cm in length. Thyone raphanus is small (only 3-4cm), has a long tail and large flat spicules with many holes. Thyone inermis has almost transparent skin with no spicules except in the tail and tentacles. See also Thyone roscovita.