<Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2017) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2017) (Learn how and when to remove this template message) </Td> </Tr> <P> Many arthropods have sclerites, or hardened body parts, which form a stiff exoskeleton made up mostly of chitin . In crustaceans, especially those of the class Malacostraca (crabs, shrimps and lobsters, for instance), the plates of the exoskeleton may be fused to form a more or less rigid carapace . Moulted carapaces of a variety of marine malacostraceans often wash up on beaches . The horseshoe crab is an arthropod of the family Limulidae . The shells or exuviae of these arachnid relatives are common in beach drift in certain areas of the world . </P> <P> Some echinoderms such as sea urchins, including heart urchins and sand dollars, have a hard "test" or shell . After the animal dies, the flesh rots out and the spines fall off, and then fairly often the empty test washes up whole onto a beach, where it can be found by a beachcomber . These tests are fragile and easily broken into pieces . </P>

How many more animals have fur than shells