Left:
Young, un-eroded specimen, diameter 5 mm with Maltese cross juvenile outline.
Four wall plates with grey central furrow (1), other species in Britain have six wall plates.
Operculum completely shut. Thin blackish triangle on scuta (2).
Cavity in tergum (3) accommodates a protrusion of the scutum.
4: carina.
5: rostrum (actually two fused rostro-lateral plates taking the place of a rostrum lost in evolution).
6: wide flat edge of rostrum creates pentagonal outline for the aperture, but on some specimens the aperture comes to a point here, creating a diamond outline/
On Fucus spiralis on sea wall near MHW, Mersey Estuary. England. October 2010.
Right: adults and juveniles. North Wirral coast, Cheshire, England. 2011.