Given the various wtf posts about tarsiers, and marmosets, and glowing rhesus macaques, here's one about a genus of primates you might not have heard about before.
Douroucoulis, small South American primates also known as Night Monkeys, & Owl Monkeys, of the genus Aotus. Aotus means earless, and their ears are indeed quite small. On the other hand, they do have large eyes, because they're the world's only nocturnal monkeys. There are plenty of nocturnal prosimians out there - tarsiers, galagos, aye-ayes, lorises, and so on, but only the Aotidae have gone back to nocturnalism from amongst the true monkeys. They're so specialised to feed and move at night they've lost all their colour vision.
They're of considerable interest medically, as well, since they're vulnerable to the same species of malaria that we are.
Douroucoulis are very affectionate monkeys too, with strong pair-bonding. Further, they're one of the few monkeys in which the father does most of the parental care, only handing the baby back to mum when it needs to be fed. One of the ways they maintain the pairbond is by kissing. A lot of kissing. A constant orgy of liplocking, a surfeit of suck-face. They can hardly keep their hands off each other. That doesn't stop other owl monkeys ( of either gender) trying to muscle in, and ousting the resident adult. THAT can get quite brutal. But since the new pair stays as monogamous as they were with the old partner, and they'll only have one baby a year, owl monkeys are also unusual in having a very low sperm count. Why waste time making more?