guinea pig (gĬn´ē), domesticated form of the cavy, Cavia porcellus, a South American rodent. It is unrelated to the pig; the name may refer to its shrill squeal. Guinea pigs were raised by the Incas and have long been used as food in South America. They were first imported into Europe from Guiana in the 16th cent. There are a number of varieties, some with short, smooth hair and others with longer hair, and a great range of color combinations, including mixtures of black and white and many shades of brown. They have rounded bodies, large heads, and blunt noses and reach a length of 6 to 10 in. (15–25 cm) and a weight of 1 to 2 lb (450–900 grams). Females produce three to five litters, usually of three or four young, per year. The guinea pig's rapid reproductive rate and high resistance to disease make it a valuable laboratory animal; it is used for testing serums and antitoxins and for experiments in genetics and nutrition. It is also sometimes kept as a pet. It is classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Caviidae.