Biodiversity & Conservation

Ocnus planci aggregations on sheltered sublittoral muddy sediment



Image Dominic Counsell - Aggregation of Ocnus planci on broken shell and cobbles. Image width ca 40 cm.
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Distribution map

SS.IMU.MarMu.Ocn recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • EC_Habitats

Text page icon Habitat description

Map icon Distribution of biotope in Britain and Ireland Recorded from Wide Firth in Orkney; Carlingford Lough, Northern Ireland, and Loch Goil, Loch Craignish, and Loch Erisort in western Scotland.
National importance Rare

Text page icon Description of biotope

For a full description of this biotope including characterizing species, distribution, survey information and references visit JNCC

Dense aggregations of Ocnus planci (or Ocnus brunneus?) on various substrata, typically muddy but sometimes with stones or shells, in sheltered conditions such as sea lochs. Associated species vary but are typical of very sheltered muddy habitats. Melanella alba, which parasitises holothurians, was found in large numbers at one site. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Additional information icon Additional information

The description of this biotope is based on only four records (Erwin et al., 1990; Connor et al., 1997a). The taxonomic status of Ocnus planci and Ocnus brunneus is under review and the species may have been confused. However, the two species are ecologically similar and have been discussed together for the sake of this review.

This review can be cited as follows:

Tyler-Walters, H. 2002. Ocnus planci aggregations on sheltered sublittoral muddy sediment. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 29/11/2015]. Available from: <>