(Düben & Koren, 1845)
Body elongate and tapering at both ends, usually bending upwards in a U-shape; especially the posterior end is long and thin; up to 150 mm in length and about 10 mm thick; usually coloured dark-brownish.
There are 10 short, sparsely branched tentacles (T. elongata tentacles).
The tube-feet are not quite retractile and are arranged in 5 distinct rows, towards the ends more zigzag.
The skin contains 3 kinds of calcareous deposits: (1) In the deeper parts of the skin there is a close layer of somewhat irregular, smooth plates with numerous small holes. (2) Above this layer some smaller, rounded plates with few holes are scattered. (3) In the superficial layer there are numerous small cup-shaped bodies. Transitional forms between plates have also been found (T. elongata spicules).
This species lives on muddy bottoms where it lies burried with only the anterior and posterior ends above the surface; from 0-65 m.
In the North Sea this species is found from the Shetland Islands down to Durham on the British east coast, and Helgoland. Elsewhere it is distributed from Norway to the Mediterranean.
Unique in shape, cannot be confused with any other species.