Meeting Abstract

32.2  Tuesday, Jan. 5  Filter feeding in hemichordate worms and the evolution of the vertebrate adenohypophysis GONZALEZ, P; CAMERON*, CB**; Université de Montréal; Université de Montréal c.cameron@umontreal.ca

Observations on the hemichordate worm Protoglossus graveolens demonstrate that the gill slits, pre-oral ciliary organ and the lining of the cylindrical pharynx are used in filter feeding. Pumping of water is generated by cilia that line the lateral gill bars and the pre-oral ciliary organ directs water from the dorsal surface of the proboscis to the mouth. Particles are trapped and concentrated on the primary and secondary gill bars and transported ventrally and posteriorly by cilia that line the pharynx. Particles that passed freely through the gill pores were maximum 1.28 μm and water entered the pharynx at a rate up to 4.05 mm.s-1. The Reynolds number and propulsive efficiency of the filter-feeding structures is similar to other filter feeders. Structural and functional similarities with the cephalochordate pharynx suggest that a wheel organ/ pre-oral ciliary organ and a filter-feeding pharynx may have been present in the common ancestor to the deuterostomes. Immunohistochemical studies using antibodies against Pit1 and FSH further suggest that the adenohypophysis of vertebrates evolved from an enteropneust-like pre-oral ciliary organ/ cephalochordate wheel organ.