It is found on the middle and lower regions of the shore, under stones and in shingle and is common round the coasts of Britain and Ireland.

The dorsal surface of the body is rounded and brown with longitudinal streaks and a faint iridescence.

It is usually beneath stones and boulders, in rock crevices and fissures, among the holdfasts of Laminaria, among the byssus threads of Mytilus colonies or on a variety of soft substrates including sand, silty-sand, shelly-gravel and shingle.

Movement is performed by small waves of muscular contraction that flow along the body from tail to head.

Several waves may occur simultaneously and the worm glides forward slowly and smoothly, the swellings running evenly along the body.