Planc's Brown Sea Cucumber

Overview

Planc's Brown Sea Cucumber is a distinctive echinoderm often found in sheltered marine environments. It is recognized by its cylindrical, leathery body and specialized feeding tentacles used to capture suspended organic matter.

Distribution & habitat

This species is native to the temperate waters of the northeastern Atlantic Ocean and the Mediterranean Sea. It typically inhabits soft, muddy sediments, but it is also frequently observed attached to hard substrates such as pebbles, cobbles, shells, or the fronds of algae in areas with moderate to weak water flow.

Appearance

The body is cylindrical and can reach up to 15 cm in length, with a smooth, leathery texture that may appear slightly angular. Its coloration is generally russet or dark brown, sometimes marked with irregular dark patches or lines. It features ten branched, leaf-like feeding tentacles—eight large and two small—which are typically lighter in color than the body. The tube feet are retractile and arranged in five double rows along the body.

Biology & behavior

Planc's Brown Sea Cucumber is a suspension feeder, using its branched tentacles to trap plankton and detritus from the water column. It is generally not very mobile and often lives in groups. A notable biological feature is the existence of a smaller, neotenous form historically referred to as Ocnus brunneus. This smaller variant, which retains juvenile characteristics like a single row of tube feet, is believed to reproduce asexually through transverse division, whereas the larger, sexually mature form reproduces via external fertilization.