Description: A brown epifaunal sea cucumber with a smooth skin and 10 small tentacles. In larger specimens the tube-feet are in five double rows but a small, apparently neotenous form (called Ocnus brunneus) is known which looks exactly like Ocnus lactea but is brown. The two species often occur together. The spicules are knobbly but have more than 4 holes. Up to 8cm, neotenous form 1cm.

Habitat: Not well-defined but apparently epifaunal on algae, shells, worm-tubes and other sessile invertebrates in sheltered sites.

Distribution: Western coasts of the British Isles, Irish Sea and Dogger Bank. Further distribution includes the Mediterranean. Apparently the small neotenous form, which is believed to only reproduce by transverse division, has a more northerly distribution than the normal, sexually reproducing form. Confusion with Ocnus lactea has resulted in information about these species being mixed up.

Similar Species: See comments above about Ocnus lactea.

Key Identification Features:

• Epifaunal habit.
• Brown coloration.
• Tube-feet in 5 double rows.(Zigzag in small specimens.)
• Spicules knobbly with more than 4 holes.

Distribution Map from NBN: Ocnus planci at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Ocnus planci at iNaturalist World Species Observations database.

WoRMS: Ocnus planci at World Register of Marine Species. Accepted name: Ocnus planci (Brandt, 1835). AphiaID: 124647.

Classification: Biota; Animalia; Echinodermata; Echinozoa; Holothuroidea; Actinopoda; Dendrochirotida; Cucumariidae; Ocnus