web-footed marsh rat

This is a medium sized species compared with other members of the genus; the head-and-body length is between 167 and 211 mm (6.6 and 8.3 in) and the tail length is between 183 and 214 mm (7.2 and 8.4 in). The fur is luxuriant and dense. The dorsal colour is cinnamon, the flanks are a brighter orange and the underparts a paler orange, apart from a white throat and chest and some white in the unguinal area.

H. brasiliensis is semiaquatic and occurs in eastern and southern Brazil, Uruguay, eastern Paraguay and northeastern Argentina in the Atlantic Forest Ecoregion. It is typically found in swampy grassland and woodland areas bordering rivers in the rainforest, both on the coastal plain and inland.

A nocturnal species, H. brasiliensis moves freely on land and in the water. It is seldom caught in live traps but is frequently caught by barn owls and mammalian carnivores. It feeds on tender shoots and mostly breeds after rains in spring and summer, with litters of three to six young having been recorded. It can be a pest in sugar cane and rice crops.