Male, female and young all of different form; each with only five pairs of ambulatory pereiopods. Cephalon fused with two pereion segments, limbs of the second fused segment modified as flattened pylopods, which cover the mouthparts ventrally. Adult male pylopod of 2 or 3 articles. Male with the front of the cephalon having a median tooth bordered by a shallow concavity on each side; lateral corners square. Cephalon broader than long and with a pronounced ridge over each eye. Lateral tooth of mandible somewhat indistinct. Last pereion segment reduced and without limbs; best seen in males, where it is narrow and equal in width to the pleon segments. Male with large mandibles, which project in front of the cephalon and are forceps-like. Females and late pranizas (young ones) with the pereion segments 3 to 5 fused and inflated, particularly in females, which incubate the eggs internally. Male body length 2.4 to 5.4 mm; females 3.9 mm.
Most records are from dredged material among which it is probably the most common gnathiid.
Ranging northwards to the Barents Sea and southwards to the Mediterranean.