Adult carapaces strongly dimorphic, males smaller 0.55-0.6 mm long than females 0.62-0.7 mm long; conspicuously flattened ventrally. Males moderately inflated, with greatest width at mid-length; females strongly inflated behind mid-length. Dorsal margin evenly arched in both sexes, ventral margin straight or weakly sinuous; posterior margin well-rounded in female, more angular in male. Living specimens are translucent white with a red/brown patch behind the eye. Posterior vestibulum unusually broad; posteroventral marginal pore canals short and simple.
Recorded almost exclusively from water of 20-60 metres depth, associated with coarse substrates and algae.
Frequently found around the coasts of Britain, especially in the north, and Scandinavia.