Meeting Abstract

66.2  Tuesday, Jan. 6  Development and Evolution of Ptychoderid Hemichordates SWALLA, B.J.; Univ. of Washington bjswalla@u.washington.edu

Hemichordata are the sister group to Echinodermata, yet share some morphological features with Chordata, including gill slits. Hemichordates contain both solitary enteropneust worms and colonial pterobranchs, but molecular phylogenies suggest that the colonial pterobranchs are a sister group to the direct developing Harrimaniidae, including the saccoglossid worms. We have been investigating the relationships within and between Ptychoderidae, the enteropneust family that includes Glossobalanus, Balanoglossus and Ptychodera. These complex enteropneusts have ciliated feeding larvae, similar to echinoderm larvae. Their metamorphosis converts a planktonic larva into a benthic, burrowing worm. We are identifying external and internal morphological characters that typify the three genera of ptychoderids, in order to construct taxonomic keys for identification of these enteropneust worms. In addition, we following the developmental origins of morphological characters in the larva and following metamorphosis. For example, ptychoderid worms have a complex collar nervous system that contains giant cells, and may or may not contain hollow cavities within it. Ptychoderid enteropneust worms also show increased ability to regenerate anterior structures when amputated, compared to saccoglossid worms. We believe that understanding the developmental origin of specific tissues and structures will allow insight into their possible homologies with chordate characters.