Black-tufted or black-pencilled marmosets are found in the central and coastal region of Brazil but relatively far inland from the ocean. They live high up in rainforest trees, and are seldom seen far below the upper canopy or anywhere near the ground. This species is usually found in gallery forest: the trees that grow in narrow strips beside rivers, and which are frequently flooded. It grows to be between 7 and 9 inches (18 – 23cm) long and weighs about 12 ounces (350g) on average.

The marmoset has large black tufts behind its ears. The head is black or brown mixed with gray and white patch on the forehead and the body is gray/brown. The long tail is ringed with black and grey. The tail is used to help the monkey balance as it moves around in the tree tops. Their preferred food is tree sap but they will eat some insects, fruit or eggs in a pinch.

The males and females form monogamous pairs. They often live in family groups with their offspring. They breed twice a year, and the older offspring assist their parents in raising their younger brothers and sisters. The young are sexually mature after just 18 months (and live around 15 years) but they can take their time choosing a suitable mate and moving off to their own range. It is also thought that the marmosets migrate to find optimal zones to inhabit depending on the environment and wet and dry seasons. In some cities of Brazil the marmosets have adapted to urban environments either as pets or other looser relations with humans.

Black-tufted marmosets mark their territory with aromatic secretions produced by glands on their chests and near the anus. This is primarily to deter other species of monkey from feeding in the area. Group members alert each other to danger, using specific cries to warn against different types of predator. Common predators are snakes, birds of prey and wild cats.