Carapace large, 0.6-0.7 mm long, thin-shelled, relatively high in proportion to length, finely pitted. Post-ocular and dorsomedian sulci distinct, posteroventral alar protuberances weak. Colour buff, dark brown or sometimes white in living specimens. Both free corners of distal process of male copulatory appendage produced and acuminate, ventral margin almost straight anteriorly, strongly convex posteriorly; free end of ejaculatory duct and proximal finger-like process relatively long (L. castanea 6 ).
An exclusively brackish-water species, found extensively in estuarine and salt-marsh environments, associated with mud and algae.
It occurs on NW European coasts from the Bay of Biscay to Norway and the Baltic; we have also seen specimens from southern Greenland.