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".
Empidoidea
Several species within Empidoidea are of particular interest to ethologists and ecologists, due to elaborate mating rituals and life histories involving freshwater.
The most familiar families in the group are the Empididae and Dolichopodidae, both of which occur worldwide and contain thousands of species. The smaller families were formerly included in the Empididae, but have since been accorded family status. The monophyly of most of these groups have since been confirmed by subsequent studies. The Brachystomatinae and Microphorinae are sometimes elevated to full family status, too, but this would apparently make the Empididae and Dolichopodidae paraphyletic and thus they are retained as subfamilies here. Atelestidae forming the sister group to the rest of Empidoidea is a unanimous result in all studies that have utilized molecular data.