Shell description

The thin shell is external and white to whitish transparent in colour, usually with a globose-elongate shape and wide aperture. The top of the shell (apex) is blunted; the oldest part of the shell (protoconch) extends out of the shell. At the bottom of the shell an umbilicus is present. The shell surface is smooth, but may have faint growth lines. The length of the shell varies between 2–3.3 mm.

Animal description

The body is white in colour. The foot is branched in the hind part, and the cephalic shield has tentacle-like lobes in the rear part.

Anatomy

The radula consists of 12 rows of teeth, with one inner lateral tooth on each side and one central (rachidian) tooth. The outer lateral teeth are absent. The lateral teeth are long and the inner edge carries denticles. The central tooth has two lobes that bear coarse denticles; the lobes are separated by a gap. The radula is asymmetrical as the left laterals are slightly smaller than the right lateral teeth. The male reproductive system consists of a short, elongate penis chamber that splits to form a prostate with two coiled branches. One branch is thick and has a blunt end, while the other is thin and has a bulky lump at the end.

Ecology

This species can be found from the intertidal down to 350 m in tide pools, on mire, pebbles, mud, sand, clay, shell gravel, algae and stones with Corallina (calcareous algae).

Geographical distribution

Occurs in Norway along the entire coastline; the British Isles southwards to the Mediterranean Sea and the Canary Islands. This species is circumpolar occurring from New England, USA, over Greenland, Iceland, the Barents Sea, White Sea, Kara Sea, Laptev Sea to the east Siberian Seas, down to Japan, and British Columbia, Canada. 

References

Ohnheiser, L. T. & Malaquias, M. A. E. 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.