This subfamily consists of two species in two separate genera;
Genus Heterotis : Heterotis niloticus
Genus Arapaima : Arapaima gigas
Heterotis niloticus 2 (Cuvier, 1829) is the only species of the genus but gives the name to the subfamily whose other member is Arapaima gigas. It has a terminal mouth and long unpaired fins nearly equal in length. It grows up to about 90 cm and is a nest-builder and an air-breather like Arapaima, but lives in Africa instead of South America. Remarkable is the fourth gill arch which is spiral shaped and works as a filter apparatus to concentrate the tiny phytoplankton, its diet, and wrap it into a layer of mucilage before swallowing it.
Arapaima gigas 2 (Cuvier, 1829), also is the only species of the genus. Its snout looks duck-like and in the females the head bears pale, milky fields of glands which secrete a food for the fry. (Arapaima gigas head ) The colour is a dark metallic-green. With a size of about 4 meters this is one of the largest living freshwater fishes and may reach 200 kg in weight.