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

Abstract

Cloudina, an important Ediacaran index fossil, is considered as one of the earliest biomineralizing 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, ultrastructure and biomineralization suggest that Cloudina is not closely related to any recent skeletal annelid (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 origin (base) in Cloudina is also compatible with the hypothesis of an animal of cnidarian grade.