WOODIN, S.A.*; MERZ, R.A.; Univ. South Carolina, Columbia; Swarthmore College, Pennsylvania: Setal function, phylogeny, and lifestyle revelations among the worms
The distinct and diverse morphology of polychaete setae and their orientations and distributions on the bodies of worms are both physical evidence of the relatedness of these worms and, depending on setal type, an indication of the lifestyle of their bearers. Being able to view setae in these two ways makes it particularly intriguing to understand the relationship between the patterns of setal diversity, their functions and the mode(s) by which setae develop. The rich cladistic analysis that now exists of the Polychaeta gives us a hypothetical evolutionary map of setal diversity. Our understanding of the functional morphology of setae gives us an intimate insight to how these worms live. It also provides us with predictions about the lifestyles of basal forms. Morphologically, the two major innovations of setal design after the development of simple capillaries are hooks (which function primarily for attachment to the insides of tubes or the bodies of symbionts) and joints (which have been shown to increase the efficiency of stepping locomotion probably by allowing setal tips to conform to the irregularities of the substratum). These morphological modifications are associated with the three major radiations (sensu Rouse and Fauchald, 1997) within the polychaetes. To further understand the functional bauplan of polychaetes across different lineages and the true relationship amongst polychaete groups, we ask whether either hooks or joints arose more than once. We need to understand what genes are involved in setal production and how they differ amongst the major groupings of polychaete families.