Horse
Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus".
Zebra
There are three species of zebras: the plains zebra, the mountain zebra and the Grévy's zebra. The plains zebra and the mountain zebra belong to the subgenus "Hippotigris", while Grévy's zebra is the sole species of subgenus "Dolichohippus". The latter resembles an ass, to which zebras are closely related, while the former two look more horse-like. All three belong to the genus "Equus", along with other living equids.