cavy, name for 14 species of South American rodents of the family Caviidae, including the domestic guinea pig. The wild cavies are usually small, rounded, and tailless, with fur of a uniform shade of brown. Nocturnal animals, they occupy a variety of habitats, especially dense vegetation. An unusual, large species is the Patagonian cavy, or mara (Dolichotis patagonum), a long-legged, harelike animal that reaches a length of about 21/2 ft (76 cm) and lives in arid regions. The capybara belongs to a related family. Some cavies are hunted for food in South America. Cavies are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Caviidae.