Three subspecies have traditionally been recognised but their distribution is peculiarly disjunct and has been considered a biogeographical puzzle, with one population on the island of Bioko (Equatorial Guinea), a second in the Niger River Delta in southern Nigeria, and a third in the east-central Republic of Congo.

[2] The word "colobus" comes from Greek κολοβός, meaning "cut short", and is so named because of the significant reduction in size, or complete lack of an opposable thumb in comparison to other primates.

[6] To make up for this, they have four long digits that align to form a strong hook, allowing them to easily grasp branches and climb.

The colouration varies between subspecies, being black or some shade of brown with chestnut-brown or reddish face, arms and legs and pale underparts.

The nominate subspecies, P. p. pennantii is endemic to Bioko, an island 32 kilometres (20 mi) off the coast of Equatorial Guinea.

The monkeys are largely restricted to the south-west part of the island and have a total range of less than 500 square kilometres (190 sq mi).

They have specialist teeth that can macerate leaves and break up tough but pliant unripe fruit and the seeds embedded in the flesh.

They tend to select foliage with a high protein to fibre ratio and a low tannin content.