The origin and body plan evolution of brachiopods

Recent hypotheses regarding the origin and body plan evolution of brachiopods are reviewed. Brachiopods are firmly placed within the lophotrochozoa, one of three major bilaterian lineages revealed by molecular phylogeny. Comparisons of mitochondrial gene arrangements further suggest that brachiopods are closer to annelids than to molluscs, a scheme supported by morphological comparisons of Cambrian fossils, including those of halkieriids and wiwaxiids. Any scenario explaining the brachiopod origin may involve curling of the dorso-ventral axis along the anterior-posterior axis. This hypothesis could partly be tested by methods of molecular developmental biology. Some potential pitfalls of this approach are discussed with reference to the deuterostome-like features of brachiopods and to the ubiquity of co-option of developmentally important genes