The fur of the Black-tailed Marmoset is colored dark brown, with a striking white or yellow-white hip stripe extending down front and inner thigh, with a black tail. Remarkable is its naked, flesh-colored ears which stand out from the skin. They reach a size of 18 to 28 cm and weigh from 300 to 400 g.
Black-tailed Marmosets are diurnal and arboreal, using their claws to climb trees. Originally rain forest inhabitants, plantations have caused them to expanded them their range. They spend the night in tree hollows or in very close vegetation. They live together in small groups and mark their territory with scent glands, driving out intruders by shouting or by facial expressions (lowered brows and guarded lips).
The diet of the Black-tailed Marmoset predominantly consists of tree sap. To a lesser extent, they also eat bird eggs, fruits, insects, and small vertebrates.
After a 145 day gestation period, the female bears two (or rarely three) offspring. As is the case for many callitrichines, the father and the other group members take part with the raising of the offspring. Within six months the young are weaned, with full maturity coming at about two years of age.
