Inconsistencies in proposed annelid affinities of early biomineralized organism Cloudina (Ediacaran): structural and ontogenetic evidences

Cloudina, an important Ediacaran index fossil, is considered as one of the earliest biominera-lizing organisms. Its biological affinities have not been fully resolved and phylogenetic links with both annelids and cnidarians have traditionally been suggested. Differences in tube morphology, ultra-structure and biomineralization suggest that Cloudina is not closely related to any recent skeletal anne-lid (e.g., serpulids, sabellids and cirratulids) and their skeletons are not homologous. The way of asexual reproduction in Cloudina resembles more that of cnidarians. The presence of a closed tube ori-gin (base) in Cloudina is also compatible with the hypothesis of an animal of cnidarian grade-