Goeldi's marmosets are blackish or blackish-brown in color and the hair on their head and tail sometimes has red, white, or silverly brown highlights.[7] Their bodies are about 8–9 inches (20–23 cm) long, and their tails are about 10–12 inches (25–30 cm) long. They weigh about 0.4835 kg in captivity and 0.500 kg in the wild. Their digits have claw like nails except for the hallux, which serve for clinging, scansorial travel, and to extract food from trees.[8][5][9]
^Rylands AB, Mittermeier RA (2009). "The Diversity of the New World Primates (Platyrrhini)". In Garber PA, Estrada A, Bicca-Marques JC, Heymann EW, Strier KB (eds.). South American Primates: Comparative Perspectives in the Study of Behavior, Ecology, and Conservation. Springer. pp. 23–54. ISBN978-0-387-78704-6.