There are about 1000 species of these molluscs whose shells have eight overlapping plates surrounded by a hard girdle.

They feed on algae which they rasp from the substrate using a radula which can be as long as 1/3 of their body length.

Living on the seafloor of the tidal zone their shape allows them to cling to the substrate like limpets and if they do become dislodged they curl up into a ball like a woodlouse to protect their soft underparts.