The Early Cambrian Halkieria is a mollusc

Authors


Jakob Vinther, Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen, Denmark. E-mail: vinther@stud.ku.dk

Claus Nielsen, Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark. E-mail: cnielsen@zmuc.ku.dk

Abstract

Halkieria evangelista was originally interpreted as a stem-group brachiopod. It was later proposed that the brachiopods evolved from a halkieriid ancestor that curved ventrally, lost the foot and radula, developed a lophophore as a new feeding organ, and modified the sclerites to chaetae. Molluscan affinities have been discussed by a number of authors. We have studied some of the original material of Halkieria and found that all the characters that can be observed with certainty are compatible with characters in living molluscs. The combination of characters observed in Halkieria does not fit with any of the living classes of molluscs, so we propose placing it in a new class, Diplacophora. Living polyplacophorans have hairs secreted by a number of epithelial cells and containing nerve cells; they are clearly not homologous with annelid chaetae. Thus, there is no support for theories that regard Halkieria as belonging to the stem group of either the annelids or brachiopods.

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