Three species are known, found in northern Argentina, southern Brazil, Paraguay and Uruguay.

[1][2] They are as follows: Species are semiaquatic, living in and near marshes and other bodies of water.

They reach a body length of 15 to 20 cm and a tail length of 13–17 cm, and weigh 110-200 g. Fur color is dark gray on top and light gray on the underside.

Their diet consists mainly of insects; they also consume other invertebrates and plant material.

The three species differ in karyotype, with aquaticus having 2n = 32, tumidus 2n = 24[1] and meridionalis 2n = 34/36.