Thaliacea

Thaliacea is a class of marine chordates within the subphylum Tunicata, comprising the salps, pyrosomes and doliolids. Unlike their benthic relatives the ascidians, from which they are believed to have emerged, thaliaceans are free-floating (pelagic) for their entire lifespan. The group includes species with complex life cycles, with both solitary and colonial forms. Because of their pelagic and gelatinous nature they are extremely rare in the fossil record, with the first unambiguous thaliacean fossil only being reported in 2026 from the mid-Cambrian Huayuan biota.