- any of several small, squirrellike, South and Central American monkeys of the genera Callithrix, Cebuella, etc., having soft fur and a long, nonprehensile tail: some species are endangered.
- any small South American monkey of the genus Callithrix and related genera, having long hairy tails, clawed digits, and tufts of hair around the head and ears: family Callithricidae
- a related form, Cebuella pygmaea: the smallest monkey, inhabiting tropical forests of the Amazon
