The earliest ‘shellly’ fossils deserve more detailed studies than they have received. Examination of the Cambrian genus Volborthella shows that it resembles in significant characters tubes of sabellariid worms, and on this basis the morphology and ecology of the animal can be reconstructed. The Cribricyathida, which include Cloudina and range from late Precambrian to lower Cambrian, are not related to Archaeoeyatha but are polychaete worm tubes with some structural characters which resemble those of serpulids. The problematic Angustiochreida (Anabarites etc.), of similar age, also show such resemblances. The first appearance in the geological record of mineralized skeletons (‘shelly fossils’), built according to various interrelated modes in annelids and in a different manner in other Metazoa, is not a suitable stratigraphic marker. The early differentiation of annelid worms can now be documented palaeontologically.

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