The Gerbil belongs to the Rodentia (rodent) Family. There are several types of gerbils, suck as the Mongolian (The most common species in captivity), Berbera, and Dongola species.
Gerbils make great pets, too.
"A gerbil is a rodent halfway between a rat and a mouse in size. They're usually 2-4 oz, and have a slightly different facial shape than a mouse or rat. Their long tails are covered with fur and end in a tuft. Their eyes are deep black or ruby red, and they come in dozens of different colors, from regular agouti (wild rabbit brown with white belly), to black, to shades of orange, gold, cream, to color points like Siamese and Burmese! Gerbils make fun and entertaining pets for both young and old.
Gerbils are fun to watch. Their antics and family interactions can entertain you for hours. They are also incredibly friendly pets. They can be taught to climb up your shoulder and can sit there, or on your head!
Gerbils require a minimum of care. Their homes take up little space, they are low-maintenance, create little odor, and they do not need frequent vet visits. They are very friendly, social, and rarely bite, as is the case with some rodents that will remain anonymous."
-- The AGS website's Gerbil Care Handbook