The slow loris shouldn't be a difficult object of study. For one thing, it's slow—very slow (think sloth slow). And these small primates, which are unique in possessing a toxic bite to ward off predators, are charismatic due in large part to their compelling, wide-eyed faces. But they are also nocturnal, and they tend to live in hard-to-reach places, such as the rainforests of Borneo. Which might be why until recently, scientists had lumped all the slow lorises (Nycticebus) into just two species.

Currently, three more species—including the Bornean loris (N. menagensis)—and many more subspecies of this omnivore are recognized. Now a new research effort has discovered three distinct species within the formerly singular Bornean loris species. The project also uncovered one entirely new species, which has even "longer, fluffier body hair," the team of researchers noted in the study describing the find, which was published online December 13 in the American Journal of Primatology.

"Although the number of recognized species of primates has more than doubled in the past 25 years and our understanding of what defines a species has improved, some species, particularly the nocturnal ones, remain hidden to science," the researchers noted in the study. Nocturnal species are not only more difficult to study in the wild than are diurnal ones (we human primates are typically diurnal, of course), but they also often lack the distinctive markings of animals that are meant to be visible in the daytime.

So the research team, led by Rachel Munds, of the department of anthropology at the University of Missouri, Columbia, examined color photographs and museum specimens of the Bornean loris that had associated collection location information. The Bornean loris can range from 265 to 610 grams, and different proposed subspecies have been found in different, non-overlapping areas of Borneo proper (which includes parts of Indonesia, Malaysia and Brunei) as well as smaller nearby islands (belonging to the Philippines and Indonesia).

To study these slow lorises, scientists honed in on mask-like markings on the lorises' faces—especially patches of white fur. The scientists' observations on these markings support elevating two previous subspecies to distinct species (N. bancanus and N. borneanus) in addition to the actual N. menagensis. They also described an entirely new species, the exceptionally fluffy N. kayan. Its type specimens are housed at the American Museum of Natural History in New York and were collected in 1935 by Baron V. von Plessen. As the researchers noted, "the fluffiness of hair is not attributed to seasonal responses, as museum specimens observed in this study were collected throughout various times of the year." This species also has "a sharply contrasting dark black and white facemask" and hair-covered ears, which is different from the more gradated face markings of the other species and their "predominantly naked" ears. Further research could use genetic sampling of wild lorises to support these new designations.

But going into the field does not always yield easy results. "Survey work in Borneo suggests the new species are either very difficult to locate or that their numbers may be quite small," Munds said in a prepared statement. Or it could be both.

Lorises live primarily in rainforests, which are under threat of destruction. Bornean lorises are currently listed as "vulnerable" by the International Union for Conservation of Nature.

The slow lorises might seem to have their looks going for them. But their big eyes and enchantingly languid moves have made them a popular—if often illegal—pet. Vendors often reduce the toxic potential of these animals' bites by pulling out the animal's front teeth, which can cause infection, excessive bleeding and premature death. "The pet trade is a serious threat for slow lorises in Indonesia," said study collaborator K.A. Nekaris, of the department of anthropology and geography at the Oxford Brookes University in the U.K., in a prepared statement.

The addition of new species to the loris list, especially those with only the slightest distinctive features, can actually complicate regulation and protection of these animals. "Recognition of these new species raises issues regarding where to release confiscated Bornean slow lorises, as recognition by non-experts can be difficult," Nekaris noted.

Eventually, however, the new formal designations should help in protecting these unusual animals. "This finding will assist in conservation efforts for these enigmatic primates," Munds said.

The animals, however, are not entirely helpless, given their unusual toxic bite. The loris possesses a gland on its arm that produces toxins. These toxins contain inhibitors that render the toxins inert. But the animal's saliva breaks down these inhibitors so that when the animal licks the gland, the toxin is activated, giving it the potential to harm potential predators, which can include snakes, large birds and other primates (including humans). With their sharp little teeth, a bite can transfer toxin to an assailant (although it usually doesn't pose a large health risk for adults). Perhaps more a more imminent threat, however, is their debilitating adorableness in online viral videos.