Limpets have a single oval shell. They look like tiny bowls when they are empty. They are often seen in great numbers on intertidal rocks. They move about grazing on seaweed at high tide and return to exactly the same position at low tide. They grip strongly onto the rock so they can’t be washed away by powerful waves. Their strong grip also reduces gaps where their body fluid might escape as the rocks are baked by the hot sun.
Many empty limpet shells are washed up onto the beach. There are many different kinds of molluscs that are called limpets. The true limpets started with an oval shell. Other molluscs have evolved from other groups to also have oval shells.