Horse outward similarity is an unreliable measure of relatedness. 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". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
Hyundai Equus car. The limousine was available only in South Korea and Russia. The Russian version had the same price tag as the South Korean version. It is a concept vehicle customized by Rhys Millen Racing, based on Equus with 4.6 Tau engine. It included bolt-on RMR Signature Edition air intake and stainless exhaust, increased engine power by 30 hp, RMR Signature Edition embroidered headrests and floor mats, and ostrich hide leather seats with suede accents. The vehicle was unveiled in 2010 SEMA show. It is a version of 2011 Equus sedan built by Mummbles Marketing and DUB Magazine. It included Trex