[6] Likely an evolutionary adaptation for camouflage and the evasion of predators, Goeldi's marmosets are a dark-furred species, usually a blackish-gray or darker brown in color.

Superficially, the short hair on their head gives them a vague resemblance to the larger woolly monkey (Lagothrix); however, the back of their necks, their backside, and tails often display light, horizontal striping or highlights.

Their digits have claw-like nails, except for the hallux, which serves for clinging, scansorial (arboreal) movement and escape, and the extraction of certain food sources from trees, such as fruits, honey, seed pods, etc.

[3][2] Molecular phylogenetics shows that C. goeldii evolved from an ancestral callitrichine and shares this origin with marmosets making them sister taxa.

One evolutionary argument to account for their differences, states that C. goeldii conserves primitive traits such as single births and a third molar lost in many marmosets.

[11][5][12] Similarities in delayed embryonic development and secondary limb-bone ossification between C. goeldii and marmosets are evidence of their close evolutionary relationship.

[14] Biannual births occur regularly in captivity and less consistently in the wild and are attributed to postpartum estrus that allows the female to be ready to reproduce soon after parturition.

These singleton births provide the offspring with longer maternal care and weaning delay that results in faster growth rates and in turn earlier sexual maturity than the other marmosets.

Cooperative care in callitrichines is therefore necessary to help mothers recover from gestation, parturition, and lactation as well as to share the energetic cost of carrying the infant among the helpers and the father.

From birth to about 18 months old, callimicos grow faster than other marmosets in part because the energy they would otherwise invest on thermal regulation and activity costs if they were not carried by their mothers is instead directed to growth.

To the south, they have been found at the Centro de Investigación y Capacitación Río Los Amigos (or Los Amigos River Training and Research Center, CICRA), Manu National Park, and the Concesión de Conservación Rodal Semillero Tahuamanu (CCRST), in addition to adjacent and surrounding areas.

[19] This is perhaps because Goeldi's marmosets are not known to have the X-linked polymorphism which enables some individuals of other New World monkey species to see in full tri-chromatic vision.