The thick shell is external and white to whitish transparent in colour, usually with an elongate cylindrical shape, the outline narrows towards the hind and front when viewed from above. The opening is wide. The top of the shell (apex) is sunken, and the oldest part of the shell (protoconch) extends slightly out of the shell (mammilate), but not beyond its first whorl. At the bottom of the shell an umbilicus is present. The shell surface is smooth. The length of the shell varies between 3.7–5.8 mm.
The body is white in colour. The foot is branched towards the hind, and the cephalic shield has tentacle-like lobes in the hind part.
The radula consists of 11 rows of teeth, with one inner lateral tooth on each side and one central (rachidian) tooth. The inner lateral teeth are long and the inner edge carries denticles. The central tooth has two flat lobes that bear denticles; the lobes are separated by a gap which has a small pointed structure. The radula is asymmetrical as the left laterals are much smaller than the right lateral teeth, and carry one large denticle on the tip. The male reproductive system consists of a long, thin penis chamber and a rounded prostate emerging from the penis chamber at a right angle, the external sperm groove continues as an open groove along the entire penis chamber.
Occurs on mud, sand, silty sand, shell sand, clay, foraminiferans, gravel and silt at depths of 559–4268 m. It is most abundant below 2000 m depth and therefore considered a deep sea (abyssal) species.
Occurs in the Norwegian Sea, the Faroe Islands, the Denmark Strait, the North Atlantic and the Mediterranean Sea.
Ohnheiser LT og Malaquias MAE (2014). The family Diaphanidae (Gastropoda: Heterobranchia: cephalaspidea) in Europe, with A redescription of the enigmatic species colobocephalus costellatus M. Sars, 1870. Zootaxa 6(3774): 501-522. http://zoobank.org/References/1C4C791C-09D7-4711-9D05-1ABE3DB24916 DOI: 10.11646/zootaxa.3774.6.1.