Any of various primates of the suborder Strepsirrhini (formerly Prosimii), considered the most primitive primates. Prosimians have a moist, bare muzzle and a retina that lacks a fovea but is backed by a reflective layer that increases night vision. Unlike other primates, female prosimians do not menstruate because the lining of their uteri is not built up each month to prepare for possible pregnancy. Prosimians are mostly small in size, and include the lemurs, aye-ayes, indris, and lorises. The tarsiers were once classified as prosimians but are now considered more closely related to the monkeys and apes. Compare simian.