It is very similar in appearance to Lineus ruber, but the eyes are set further back on the head and are more neatly arranged.

[4] L. sanguineus occurs on the coasts of northwestern Europe, its range extending from Sweden southwards through the North Sea to the British Isles, Belgium and France.

It is also recorded in North America, including in the Bay of Fundy, in Brandy Cove, in the Digdeguash Estuary and in the Gulf of Maine,[1] as well as the Pacific coast.

It is typically found burrowing in muddy sand, including blackish sediment with a high content of organic matter, under stones and rocks, in crevices and among coralline algae in the intertidal zone, from mid-beach downwards.

[3][2] There is some uncertainty about the precise range because of the lack of exact identification of specimens, especially those collected several decades ago.