Aquatic in habits, this animal is related to the English water-rat and therefore included in the sub-family Microtinae (see Vole).
In the water-rat and agoutis it is.
All rodents, with the sole exception of the dormice, have a caecum, often of great length and sacculated,, as in hares, the water-rat and porcupines; and the long colon in some, as the hamster and water-rat, is spirally twisted upon itself near the commencement.
A third type, Prometheomys, from the Caucasus, is represented by a species of the size of a small water-rat, chestnut-brown in colour, with lighter feet, and the minute eyes covered with skin.
Voles, as typified by the water-rat and the tailed fieldmouse, are stouter built and shorter-nosed rodentsthan the typical rats and mice, with smaller ears and eyes and shorter tails; all being good burrowers.