Goeldi's Marmoset or Goeldi's Monkey (Callimico goeldii) is a small, South American New World monkey that lives in the upper Amazon Basin region of Bolivia, Brazil, Colombia, Ecuador, and Peru. It is the only species classified in the genus Callimico, and the monkeys are sometimes referred to as "callimicos".
Goeldi's Marmosets are blackish or blackish-brown in color. Their bodies are around 8 to 9 inches long (about 22 cm), and their tails are 10-12 inches long (25-30 cm).
Goeldi's Marmoset was first described in 1904, making it one of the last monkey genera to be described. In older classification schemes it was sometimes placed in its own family Callimiconidae and sometimes in the (now abandoned) family Callitrichidae, the family containing marmosets and tamarins. More recently, it has been classified into Cebidae, which now contains all the marmosets and tamarins, as well as the capuchin and squirrel monkeys.
Females reach sexual maturity at 8.5 months, males at 16.5 months. The gestation period lasts from 140 to 180 days. Unlike other New World monkeys, they have the capacity to give birth twice a year. The mother carries a single baby monkey per pregnancy, whereas most other species in the family Cebidae usually give birth to twins. The infant is weaned after about 65 days. The life expectancy in captivity is about 10 years.
Goeldi's Marmosets prefer to forage in dense scrubby undergrowth; perhaps because of this, they are rare, with groups living in separate patches of suitable habitat, separated by miles of unsuitable flora. In the wet season, their diet includes fruit, insects, spiders, lizards, frogs, and snakes. In the dry season, they feed on fungi, the only tropical primates known to depend on this source of food. They live in small social groups (approximately six individuals) that stay within a few feet of one another most of the time, staying in contact via high-pitched calls. They are also known to form polyspecific groups with tamarins, perhaps because Goeldi's Marmosets are not known to have the X-linked polymorphism which enables some indiviuals of other New World Monkey species to see in full tri-chromatic vision.