(Linné, 1758)
Description (shell):
Shell solid, with five or six slightly tumid whorls; last whorl more distinctly tumid, spire prominent, and flat-sided. Surface with numerous irregular growth lines covered by well-developed periostracum; a surface bloom, rather like that on black grapes, is a feature of all but the youngest shells. Aperture somewhat narrow, tapering sharply towards adapical region. Outer lip meets body whorl tangentially, with a thin periostracal extension along margin and a low ridge internally; inner lip reflected over columella region; both lips grooved. No umbilicus.
Size:
Up to 9 x 7 mm.
Colour:
Commonly black or dark brown; last whorl occasionally with spiral banding or vertical stripes. Uniformly pale shells may also occur. Operculum and interior of aperture dark.
Animal:
Body essentially similar to Littorina littorea ; cephalic tentacles lack transverse stripes and have two longitudinal dark lines on dorsal surface.
Habitat:
In crevices and empty barnacle cases on upper shore and in splash zone; often several metres above EHWST on exposed shores.
Distribution:
Distributed from Black Sea to western Norway. Absent from southern North Sea; on British Channel coast it does not penetrate eastwards beyond Isle of Wight. Local distribution may be patchy (Distr. M. neritoides).