There is one living species in this family, the nutria (Myocastor coypus), also known as the coypu.

They are native to Central and South America, but they have been introduced to parts of the United States, especially the southeastern United States. The nutria has also been introduced in Asia and Europe.

Nutrias are large aquatic rodents. They are about three feet in length and weigh around 30-35 pounds. They have thick, reddish-brown fur; short legs; webbed rear feet; small ears; and small eyes. They have big heads with a squared muzzle; long, round, lightly haired, pointed tails; and whiskers.

Nutrias are found near lakes, ponds, swamps, rivers, and marshes. A nutria can stay submerged underwater for several minutes, and sometimes it floats in the water with just its nose and eyes above the water.

The nutria eats land plants and aquatic plants.