The red-bellied titi monkey, Callicebus moloch, is the first species of titi monkey that has been described. Count (Graf) Johann Centurius Hoffmann von Hoffmannsegg described it in 1807 from specimens originating from Pará, Brazil. The species was described as being “mouse-grey; temples, sides of the face and undersides rust-coloured. Tail brown, on the tip like the hands, whitish”.
It has a large distribution range in Brazilian Amazonia, south of the Rio Amazonas, in the States of Pará and Mato Grosso.
The species is variable in colouration, and many species that have been described can probably be synonimized with Callicebus moloch,including emiliae, remulus, vieira, bernhardi and geoffroyi. If Callicebus moloch is used in literature, one should be prudent with the identification of the mentioned animal, as before 1990 many species of titi monkeys were considered as subspecies of C. moloch.