Flat Top Shell

• It is one of the species biologists use as an indicator of sea warming: its distribution has shifted northwards in recent decades.
• The open, deep umbilicus distinguishes it from other top shells of the same habitat.
• It is identified by its umbilicus: a deep, round hole in the centre of the shell's base, which gives it its name.
• Its shell carries oblique violet bands on a grey ground, a pattern easily recognised on Atlantic rocks.
• It scrapes the biofilm of microscopic algae off the rock with its radula, and its grazing keeps rock surfaces clear.
• Its northern limit is shifting as the sea warms, and it is used as an indicator of climate change on British coasts.

Skeleton type

Invertebrate - external calcareous shell (mollusc)

Habitat and environment

Mid and lower intertidal rocks of the north-eastern Atlantic

Sources consulted: da Costa (1778); Marine Life Information Network; Mieszkowska et al., programa MarClim; ScienceDirect (Hughes 1989); Science Advances, How colonial animals evolve; Wikipedia, Zooid; anatomia de Gastropoda