(Müller, O.F., 1776)
Description (shell):
Shell conical, apex toward anterior margin with anteriorly projecting beak (more discernible in young shells). Profile more variable than in Acmaea virginea , often showing a marked apical inflection in both posterior profile (mainly convex) and anterior profile (mainly straight). Sculpture as in Acmaea virginea (T. testudinalis-drawing).
Size:
Up to 30 x 24 x 10 mm, commonly 14 x 10 x 4 mm in littoral habitats.
Colour:
Shell with light background overlain by series of' irregularly branched brown bands radiating from apex to produce a tessellate pattern. Inside white with outside pattern visible marginally; apical region chocolate brown.
Animal:
The white animals have a large head with a pair of long tentacles and a pair of eyes at their base. Outer lips on snout with narrow, somewhat stiff, outer fringe; incomplete ventrally where a broad, lobed region bounds mouth. Mantle edge cuprous green with two staggered rows of short tentacles. The foot is oval and broad.
Habitat:
On boulders and small, smooth stones, particularly those encrusted with red algae such as Lithothamnion ; from LWNT to 50 m.
Distribution:
A circumpolar species, not in the southern North Sea (Distr. T. testudinalis).