Among these, the tuco-tucos (Ctenomys) are characterized by their burrowing habits, almost rudimentary ears, small eyes, short tails and the kidneyshaped grinding-surfaces of their cheek-teeth.
Brazil has three groups of animals similar to the common rat - the Capromydae, Loncheridae and Psammoryctidae- the best known of which is the " tuco-tuco " (Ctenomys brasiliensis), a small burrowing animal of Rio Grande do Sul which excavates long subterranean galleries and lives on roots and bulbs.
The rodents are the most numerously represented order, which includes the coypu or nutria (Myopotamus coypus), the chinchilla (Chinchilla laniger), the tuco-tuco (Ctenomys brasiliensis), a rabbit, and 12 species of mice - in all some 12 genera and 25 species.
The typical genus is represented by the degu (Octodon degus) and several nearly related species; other genera being Ctenomys, Octodontomys (Neoctodon), Aconaemys, Spalacopus and Abrocoma; the latter taking its name from its unusually soft fur.