An otter is any of 13 living species of semiaquatic (or in the case of the sea otter, aquatic) mammals that feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals.
The otter subfamily Lutrinae forms part of the family Mustelidae, which also includes weasels, badgers, wolverines, and polecats.
Read more about Otter: Nomenclature, Life Cycle, Characteristics, Species