Los loris perezosos (Nycticebus) son un género de primates perteneciente al suborden Strepsirrhini. Habitan en el sur y el sudeste de Asia, desde Bangladés y el noreste de India en el oeste hasta Filipinas en el este, y desde la provincia china de Yunnan en el norte hasta la isla de Java en el sur. Si bien varias clasificaciones anteriores reconocían menos especies, en 2013 se consideraban válidas ocho: N. coucang, N. bengalensis, N. pygmaeus, N. javanicus, N. menagensis, N. bancanus, N. borneanus y N. kayan. Sus parientes más cercanos son los demás lorisiformes, es decir, loris esbeltos, potos, falso poto, anguantibos y gálagos. Más lejanamente, se relacionan con los lémures. Su historia evolutiva es incierta debido a que el registro fósil es escaso y los estudios mediante reloj molecular han dado resultados inconsistentes. Los loris perezosos poseen una cabeza redondeada, un hocico pequeño, ojos grandes y patrones de coloración en el pelaje diferentes en cada especie. Su tronco es largo, y las extremidades anteriores y posteriores tienen casi la misma longitud, lo que les permite girar y alcanzar ramas cercanas. Sus manos y pies poseen adaptaciones para asir objetos con prensión de pinza y mantenerse agarrados a las ramas por largos periodos de tiempo. Su mordida es venenosa, una característica muy inusual en los mamíferos y que comparten solo con otros lorísidos. El origen del veneno es una toxina producida por una glándula en el brazo. Cuando el primate lame la glándula, la secreción se mezcla con la saliva y se activa. Muerden para disuadir a posibles depredadores, e incluso aplican veneno en el pelaje de las crías con el fin de protegerlas. Se desplazan despacio y silenciosamente, parándose y permaneciendo inmóviles cuando se sienten amenazados. Sus únicos depredadores documentados —aparte de los humanos— son las serpientes, las águilas-azor variable (Nisaetus cirrhatus) y los orangutanes de Sumatra (Pongo abelii), aunque se sospecha que también lo son los gatos, civetas y osos malayos. Su estructura social es aún desconocida, aunque se sabe que se comunican mediante marcas olfativas. Los machos son altamente territoriales. La gestación de los loris perezosos es prolongada y su desarrollo lento, por lo cual las crías dependen del cuidado de sus padres. Son omnívoros y comen animales pequeños, fruta y goma, entre otros alimentos. Cinco de las especies del género están clasificadas como vulnerables o en peligro de extinción en la Lista Roja de la UICN. La caza para su utilización en medicina tradicional y para su venta como mascotas exóticas representa la principal amenaza a su supervivencia, aunque también les afecta la destrucción y la fragmentación de su hábitat. Se han tomado varias medidas para preservarlos, como prohibir su venta y protegerlos del comercio internacional incluyéndolos en el Apéndice I de la CITES. Sin embargo, aún son vendidos abiertamente en mercados en el sur de Asia y trasportados como contrabando a otros países.

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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), pygmy slow loris (N. pygmaeus), Javan slow loris (N. javanicus), Philippine slow loris (N. menagensis), Bangka slow loris (N. bancanus), Bornean slow loris (N. borneanus), and Kayan River slow loris (N. kayan). 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 trunk 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 to lorisid primates. The toxin is obtained by licking a gland on their arm, and the secretion is activated by mixing with saliva. Their toxic bite is a deterrent to predators, and the toxin is also applied to the fur during grooming as a form of protection for their infants. The secretion from the arm contains a chemical related to cat allergen, but may be augmented by secondary toxins from the diet in wild individuals. Slow lorises move slowly and deliberately, making little or no noise, and when threatened, they stop moving and remain motionless. Their only documented predators—apart from humans—include snakes, changeable hawk-eagles and orangutans, although cats, civets and sun bears are suspected. Little is known about their social structure, but they are known to communicate by scent marking. Males are highly territorial. Slow lorises reproduce slowly, and the infants are initially parked on branches or carried by either parent. They are omnivores, eating small animals, fruit, tree gum, and other vegetation. Each of the slow loris species that had been identified prior to 2012 is listed as either "Vulnerable" or "Endangered" on the IUCN Red List. The three newest species are yet to be evaluated, but they arise from (and further reduce the ranks of) what was thought to be a single "vulnerable" species. All four of these are expected to be listed with at least the same, if not a higher-risk, conservation status. All slow lorises are threatened by the wildlife trade and habitat loss. Their habitat is rapidly disappearing and becoming fragmented, making it nearly impossible for slow lorises to disperse between forest fragments; unsustainable demand from the exotic pet trade and from traditional medicine has been the greatest cause for their decline. Deep-rooted beliefs about the supernatural powers of slow lorises, such as their purported abilities to ward off evil spirits or to cure wounds, have popularized their use in traditional medicine. Despite local laws prohibiting trade in slow lorises and slow loris products, as well as protection from international commercial trade under Appendix I, slow lorises are openly sold in animal markets in Southeast Asia and smuggled to other countries, such as Japan. Due in part to the large eyes that are an adaptation to their nocturnal lifestyle, they have also been popularized as 'cute' pets in viral videos on YouTube. Slow lorises have their teeth cut or pulled out for the pet trade. They make poor pets that are difficult to care for, and often die from infection, blood loss, improper handling or inadequate nutrition.

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