Otter is a common name for a carnivorous mammal in subfamily Lutrinae. The 13 extant otter species are all semiaquatic or aquatic, with diets based on fish and invertebrates. Lutrinae is a branch of the weasel family Mustelidae, which also includes weasels, martens, minks, polecats, Eurasian and American badgers, honey badgers and wolverines.