Otters are the most aquatic members of the weasel family, the Mustelidae, which contains around sixty species divided into five subfamilies: martens and weasels, badgers, the honey badger, skunks, and otters. Mammals in this family have short legs and rather long bodies, and are the characteristic small carnivore of the northern hemisphere. They're found on every continent except Antarctica; humans introduced them to Australia. The giant otter and the sea otter are the largest of all mustelids.

Like Weasels, Only Different
Aquatic though they may be, otters are still unmistakably weasels, sharing their long, streamlined body shape and an upward spinal flex at the hips that causes that typical "humpbacked" gait on land.