Developing a novel basal animal model for use in exploring the development of early sensory systems

Freshwater and marine sponges are members of the phylum Porifera, which split off of the animal lineage before the Cnidarian and the Bilaterian split (Peterson and Davidson, 2000). This makes sponges the most basal extant animal species and an excellent candidate for looking at the evolutionary conservation of ancient genes in animals. As basal animals, sponges do not have true developmental tissue layers although they do have 11 different cell types, some of which may function together (Simpson, 1984; Manconi and Pronzato, 2002). Sponges are filter feeders, and move water through their bodies so that they can absorb particles in the water column to eat. They have ciliated cells that function to move the water to the channels that run through their bodies. Water enters the sponge body through holes in the tissue called ostea, moves into choanocyte chambers, and then is moved through the body by the canals until it exits through a chimney-like osculum (Simpson, 1984; Manconi and Pronzato, 2002). Due to their role in moving water through the sponge, the choanocyte chambers are an important part of the structure and function of a sponge. These chambers are composed of flat, ciliated cells arranged in a ring (Elliot and Leys, 200). Groups of these chambers surround the ostea where the water enters the sponge (Elliot and Leys, 2009)