Hippopotamuses, often abbreviated to hippopotami or hippos, are stout, naked-skinned, and amphibious artiodactyl members (and the only living members) of the family Hippopotamidae possessing 3-chambered stomachs and walking on 4 toes on each foot. While they resemble pigs physiologically and are pseudoruminants like camels, their closest living relatives are actually the cetaceans (whales and dolphins).
There are two living species of hippopotamus in two genera; the pygmy hippopotamus (Choeropsis liberiensis) of the forests of west Africa, and the hippopotamus (Hippopotamus amphibius).
Hippopotami appear in several episodes (and 1 joke).
Several more hippos appeared in "Funny Faces".
Hippos also appear in "Crocodilian".