The upper parts are grayish black and the underparts are grayish white. The feet are long, and the middle toes of the hind feet are elongated. All the claws are long.
Females have eight mammae.
Excellent swimming ability and agility in climbing onto tall plants contribute to its success in such areas. It does not seem to make runways of its own, but follows any open route through the vegetation and frequently uses the runways of Cavia. It digs to obtain food but apparently does not excavate burrows. It may dig shallow depressions under vegetation, in which it builds nests and bears its young. It is mainly nocturnal and crepuscular, but some specimens were collected during the day.