The cotton-top tamarin is part of the most diminutive family of monkeys, Callitrichidae, the marmosets and tamarins; it weighs 432 g (15.2 oz) on average. Its head–body length is 20.8–25.9 cm (8.2–10.2 in) while its tail—which is not prehensile—is slightly longer at around 33–41 cm (13–16 in).[11] The species is not sexually dimorphic, the male and female are of a similar size and weight.[4] Members of the Callitrichinae subfamily (including this species) have sharp nails (tegulae) on all digits except the big toes, which have the flat nails (ungulae) common to other primates. Tegulae resemble a squirrel's claws and help with movement through trees.