The finding brings the number of recognized species of the teacup-size creatures -- specimens of the new species weigh less than 3 ounces -- to 20.
Because these shy, nocturnal primates look so much alike, it's only possible to tell them apart with genetic sequencing, researchers said.
"You can't really tell them apart just looking at them through binoculars in the rainforest," Peter Kappeler of the German Primate Center in Goettingen, who earned his doctorate a Duke University in North Carolina, said.
One of the new species has been name the Marohita mouse lemur, after the forest where it was found. In Malagasy, the word "marohita" means "many views," a Duke release said Tuesday.
Much of the forest home of the mouse lemur has been cleared for logging and agriculture in the last decade, prompting the International Union for the Conservation of Nature to classify the new species as "endangered" even before it was formally described.
"Despite its species' name, this mouse lemur is threatened by ongoing habitat destruction, and 'many views' of its members are unlikely," the researchers wrote in the International Journal of Primatology.