Gravel Sea Cucumber
Body elongate, cilindric, attenuating towards the ends, up to 250 mm in length; coloured yellowish-violet or whitish with brown pigment.
There are 10 large and 10 small tentacles. The tentacles are often darker than the body.
In younger specimens the tube-feet form regular double series. In larger specimens the tube-feet are more crowded in the middle part of the body, forming up to 6 double rows and leaving only a narrow naked part in the interradii.
The skin contains numerous calcareous deposits, consisting of tables with a large, smooth edged disk which are perforated by many holes, and which bear a spire composed of 4 columns. In the tentacles, the calcareous deposits consist of slender rods, which are slightly widened and perforated at the ends (N. mixta spicules).
The species lives on muddy and sandy bottoms, but also on stony bottoms and coarse gravel, at depths of about 30-200 m.
Northeastern part of the North Sea, near the British Isles including the Faeroes. Locally common in tide-swept areas of coarse shell gravel.