Guiyu oneiros is the earliest articulated bony fish discovered. The generic name Guiyu is a transliteration of the Mandarin 鬼魚 guǐyú "ghost fish" and the specific name oneiros is from Greek ὄνειρος "dream". Fossils of Guiyu have been found in what is now Qujing, Yunnan, China, in a late Silurian marine strata, about 419 million years old. Guiyu remains have been found articulated, missing only the caudal fin. The living fish is estimated to have been 33 cm long.