Yunnanozoon lividum (Yunnan + Greek ζῷον zôion (animal), with species name Latin lividum; (lead-coloured), referring to preserved colour of specimens[1]) is an extinct species of bilaterian animal from the Lower Cambrian Chengjiang biota of Yunnan province, China.

The front half of the body had rod-like structures running along the top and bottom, which were probably sclerotized.

[2] Yunnanozoon was described by Hou, Ramskold & Bergstrom in 1991, who considered its placement to be incertae sedis within Metazoa.

However a comprehensive study of yunnanozoans in 2015 found that the number of filamentous arches and circular structures were the same in all yunnanozoans examined and that the supposed "pharyngeal teeth" were instead remnants of other structures, suggesting that there was only one species, Yunnanozoon lividum, with both Haikouella species being junior synonyms of it.

[6] A 2024 study motivated by a reinterpretation of the fossil Pikaia placed Yunnanozoon as a transitional stem-chordate form between a paraphyletic Vetulicolia and the more crownward Chordata as shown on this simplified cladogram:[7][8] Banffia† Heteromorphus† Skeemella† Nesonektris† Vetulicolidae† Didazoon† Pomatrum† Yuyuanozoon† Yunnanozoon† Cathaymyrus† Pikaia† Cephalochordata Tunicata Metaspriggina† Myllokunmingia† Vertebrata Yunannozoon is suggested to have used its filamentous arches to feed with the openings on the side of the body being used to expel water.