Thyone fusus

(O.F. M├╝ller, 1776)

Body ovoid, tappering at both ends but the posterior end not ressembling a long 'tail'; up to 200 mm in length; coloured whitish, pinkish or brown.

There are 10 delicately branched tentacles, all of one colour.

The tube-feet are scattered over the whole body, but may be arranged in more or less distinct longitudinal series.

The skin is very delicate, with few calcareous deposits which consist of small, smooth tables with usually 4 holes and a spire formed by 2 rods which unite at their upper end, and which sometimes bear thorns. The tables are also found in the tube-feet (T. fusus spicules).

Sheltered sites. This species is usually found on shell bottoms where it covers itself with shell fragments or/and mud; from 10-615 m.

In the North Sea this species is known from the Shetland Islands down to Northumberland on the British east coast. Elsewhere it is distributed from Norway to Madeira and the Mediterranean.

Several Thyone species are very similar in shape and some species names could turned out to be synonyms. Thyone inermis has an almost transparent skin with no spicules except in the tail and tentacles.
Pseudothyone raphanus is a considerably small species of only 30-40 mm and has a long "tail" and large flat spicules with many holes.