Gravel Sea Cucumber

Gravel Sea Cucumber

Latin name: Neopentadactyla mixta
Global Distribution: South, west and north coasts of the British Isles, the Faeroe Islands, the west coast of Norway (Molde) and the Atlantic coasts of France
UK Distribution: West coast of Scotland to Orkney and Shetland. A few isolated records from the east coast. Also from SW England, SW and NW Wales. In Ireland, particularly Kilkieran Bay, round the north and north-east, also the SE and SW corners
Size: Up to 20cm
Diet: Suspension feeder
Habitat: Coarse, typically mobile shell, sand, gravel or maerl where tidal flow is quite strong.

The gravel sea cucumber lives in the substratum with only its tentacles visible when extended. It can quickly pull them in if threatened. Its body has numerous calcareous deposits on the skin and tapers towards either end.  Around the mouth, there are profusely branching tentacles. The cucumber mops the surface on which it is feeding with its mucus-covered tentacles before drawing them back, one at a time, into the mouth to be sucked clean of any particles. The gravel sea cucumber can move along the seabed by using its ‘tube feet’ which are fluid-filled muscular tubes with suckers.

If this sea creature wants to squeeze through narrow cracks, it can make its body soft and very flexible and if it wants to bury its body in the seabed, it can make its body hard and stiff. It does this by using a compound in their skin called catch collagen – this tissue is under neurological control and is capable of changing from a ‘liquid’ to a ‘solid’ form very quickly. When a sea cucumber is really threatened, it can respond by ingesting a great volume of water and physically rupturing (literally exploding) the hind gut to expel these tubules and a soup of defensive chemicals that are intended to prevent the predator from ever wanting to prey on a sea cucumber again.

Fun facts

  • For some unknown reason this sea cucumber undergoes some sort of hibernation during the winter.