Evolution of Biomineralization in Lophophorates

Abstract

Abstract: Improved knowledge of the fossil record, com-bined with molecular trees describing the phylogenetic rela-tionships between recent phyla, is gradually advancing ourunderstanding of the evolution of biomineralized marineinvertebrates. However, relationships between the threeextant ‘lophophorate’ phyla – Brachiopoda, Bryozoa andPhoronida – have yet to be resolved, and the monophyleticstatus of Lophophorata has been called into question. Here,we review the phylogeny and biomineralization of lophoph-orates, along with some extinct groups that have been sug-gested to be lophophorates on the basis of skeletalstructure and ultrastructure. We conclude that biomineral-ized skeletons are not homologous in lophophorates, theskeletons of brachiopods being plesiomorphic, whereasbiomineralization in bryozoans is apomorphic and hasevolved independently twice from soft-bodied, ctenostome-grade bryozoan ancestors. Phoronida nests within Brachio-poda, according to the molecular tree, and between twoclades (rhynchonelliformeans and craniiformians) havingcalcareous shells, in which case stem-group phoronidswould likely have possessed calcareous skeletons too.Both the solitary, vermiform Tentaculitoidea (Ordovician–Jurassic) and the colonial, bryozoan-like Hederelloidea(Silurian–Permian) are here considered to be biomineral-ized stem-group phoronids.