Coypu: Myocastoridae

The coypu, sometimes called the South American beaver or nutria, looks like a muskrat, only larger. It has a stout body that is highly arched and a large, somewhat triangular head. It has small eyes and ears on the upper part of its head. Coypus have a head and body length of 1.4 to 2.1 feet (43 to 63.6 centimeters), and a tail length of 0.8 to 1.4 feet (25.5 to 42.5 centimeters. They weigh from 11 to 37 pounds (5 to 17 kilograms).

They have short, hairless legs with the hind feet longer than the front feet. Each hind foot has five toes, four of which are connected by webbing. The fifth toe is used for grooming. The front feet have four long, flexible toes without webbing, and a non-functioning thumb. Their tails are long, round, and hairless. One of the coypu's most distinguishing features is its large, wide, bright orange incisors, the flat, sharp-edged teeth at the front of the mouth used for gnawing and cutting and tearing food. They can close their lips behind the incisors, allowing them to gnaw while underwater. Their ears, nose, and nostrils are located near the top of the head so they are above water when the coypu is swimming.

Coypus have two types of hair; soft, dense under fur, and outer fur of long, course, bristly hair, called guard hair. The undercoat is dark gray and the outer coat is various shades of red, brown and yellow. The stomach fur is soft and dense and usually a pale yellow. The fur on the chin and around the nose is usually white.