Yuyuanozoon magnificissimi, from the Cambrian Stage 3 Chengjiang lagerstatte, is the largest known vetulicolian, an extinct species of marine animal, with specimens up to 20 cm in length compared to 5–14 cm for other vetulicolian species.

The specific name, magnificissimi, translates as "magnificent," in reference to the great size of the holotype.

[2] Its body is non-biomineralized and consists of an elongate ovoid anterior section, with a segmented posterior section roughly one-third of the width and half the length of the anterior.

It was originally placed incertae sedis with in the phylum Vetulicolia,[2] then moved under the Vetulicolidae in a comprehensive review of the phylum,[4] and most recently reassigned to the Didazoonidae based on additional specimens that clearly show the details of the anterior opening as well as annulations on each posterior segment.

[5] A 2024 study has found the Didazoonidae to be a paraphyletic grade of the vetulicolians closest to crownward chordates as shown in this simplified cladogram:[6] Banffia† Heteromorphus† Skeemella† Nesonektris† Vetulicolidae† Didazoon† Pomatrum† Yuyuanozoon† Yunnanozoon† Cathaymyrus† Pikaia† Chordata(crown group) An earlier study in 2014 placed vetulicolians as the sister-group to tunicates, but was unable to resolve any relationships among vetulicolians as a group:[7] Vetulicola† Beidazoon† Ooedigera† Pomatrum† / Xidazoon† Didazoon† Yuyuanozoon† Banffia† Heteromorphus† Nesonektris† Tunicata