Harbor seals, Phoca vitulina, inhabit coastal waters and inland waterways of North America and northern Eurasia. It spends more time in shallow waters and on land than does any other seal. The harbor seal is a "true seal," and is more diverse and widely distributed than most marine, aquatic animals. Harbor seals are also called earless seals because they lack external ears. True seals are especially numerous in the colder waters (above 40 degrees latitude) of both hemispheres, with concentrations in the polar regions. The hind limbs of true seals are turned permanently backward and cannot be pivoted forward under the body to help propel the animals across land. Therefore, they must use a wriggling or hunching movement, rolling or sliding whenever possible, when progressing over land. Fish, crustaceans, and squid are their most important food items.