Slow lorises are a group of several species of nocturnal strepsirrhine primates that make up the genus Nycticebus. Found in Southeast Asia and bordering areas, they range from Bangladesh and Northeast India in the west to the Sulu Archipelago in the Philippines in the east, and from Yunnan province in China in the north to the island of Java in the south. Although many previous classifications recognized as few as a single all-inclusive species, there are now at least eight that are considered valid: the Sunda slow loris (N. coucang), Bengal slow loris (N. bengalensis), Javan slow loris (N. javanicus), Philippine slow loris (N. menagensis), Bangka slow loris (N. bancanus), Bornean slow loris (N. borneanus), Kayan River slow loris (N. kayan) and Sumatran slow loris (N. hilleri). A ninth species, the pygmy slow loris (X. pygmaeus), was recently moved to the new genus Xanthonycticebus. After the pygmy slow loris, the group's closest relatives are the slender lorises of southern India and Sri Lanka. Their next closest relatives are the African lorisids, the pottos, false pottos, and angwantibos. They are less closely related to the remaining lorisoids (the various types of galago), and more distantly to the lemurs of Madagascar. Their evolutionary history is uncertain since their fossil record is patchy and molecular clock studies have given inconsistent results.
Slow lorises have a round head, a narrow snout, large eyes, and a variety of distinctive coloration patterns that are species-dependent. Their arms and legs are nearly equal in length, and their torso is long and flexible, allowing them to twist and extend to nearby branches. The hands and feet of slow lorises have several adaptations that give them a pincer-like grip and enable them to grasp branches for long periods of time. Slow lorises have a toxic bite, a trait rare among mammals and unique among the primates. The toxin is obtained by licking a sweat gland on their arm, and the secretion is activated by mixing with saliva.