The nineteen species in the genus Marmosa are relatively small Neotropic members of the family Didelphidae. This genus is one of three that are known as mouse opossums. The others are Thylamys (the "fat-tailed mouse opossums") and Tlacuatzin, the grayish mouse opossum. Members of the genus Marmosops used to be called "slender mouse opossums", but are now just called "slender opossums". The six members of the Marmosa subgenus Micoureus, known as "woolly mouse opossums", were formerly considered to be a separate genus, but were moved into Marmosa in 2009. Based on a comparison of sequences of one mitochondrial and three nuclear genes, three new subgenera, Eomarmosa, Exulomarmosa and Stegomarmosa, were recognized by Voss et al. in 2014. Eomarmosa and Exulomarmosa, as well as Marmosa and Micou