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

Species indicative of sensitivity

To assess the sensitivity of the biotope, the sensitivity of component species is reviewed. Those species that are considered to be particularly indicative of the sensitivity of the biotope, and for which research has been undertaken in detail are shown below (see selection criteria). The biology of other component species of the biotope is also taken into account wherever information is known to the researcher.

Species found especially in this biotope

  • Ocnus planci
  • Melanella alba
Community Importance Species name Common Name
Important characterizing Ocnus planci A sea cucumber


This community is characterized by the abundance of Ocnus planci (or Ocnus brunneus). Loss of the Ocnus population would result in loss of the biotope as described and, therefore Ocnus has been considered to be important characterizing.

The other species in the community are common and characteristic of the wave sheltered muddy habitats in which the biotope is found. Therefore, the dominant associated species vary with location and have little significant association with the Ocnus population itself. Reference has been made to Nemertesia ramosa to represent hydroids, Virgularia mirabilis to represent sea pens, Pomatoceros triqueter to represent tubeworms, Ciona intestinalis to represent ascidians, and Alcyonium digitatum to represent anthozoans, and Echinus esculentus, Ophiothrix fragilis, Amphiura filiformis and Neopentadactyla mixta to represent echinoderms.

Additional information

The MNCR recorded 131 species within this biotope, although not all species occurred in all records of the biotope.

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 25/11/2015]. Available from: <>