Meeting Abstract

116.1  Monday, Jan. 7  Can greater relative complexity in skeletal structure explain why hexactinellid molecular-based phylogenies correspond better to traditional systematics, as compared to other sponge groups? COLLINS, A.G.*; DOHRMANN, M.; National Systematics Lab; Smithsonian collinsa@si.edu

Continuous efforts over the past two decades let us improve the systematics of sponges through the simultaneous consideration of phylogenetic hypotheses and the distribution of morphological characters. For Demospongiae and Calcarea, molecular studies suggest that a fairly large number of higher-level taxa are not monophyletic. In contrast, for Hexactinellida (glass sponges) there is a relatively closer match between clades suggested by molecular analyses and traditionally defined taxa. One hypothesis to explain these contrasting situations is that hexactinellids exhibit a more complex set of characters used in traditional taxonomy, as compared to other sponges. Defining and measuring complexity is far from simple, but we attempt to quantify the relative complexity of those characters (body form, skeletal architecture, and spicule form) used in traditional taxonomy of sponges. We focus on structural complexity, as opposed to functional, emphasizing pattern over process, and attempt to measure the overall differentiation of these characters within clades. We quantify, albeit crudely, sponge skeletal complexity, defined as the length of the shortest complete description of an entity, by tabulating the number of terms used to describe it. Somewhat against expectations, we find that the lexicon used to describe demosponge skeletal structure is more than two times that of hexactinellids, suggesting the demosponges are both more diverse (structurally) and species rich than hexactinellids. If one normalizes by species richness, hexactinellid complexity greatly exceeds that of both demosponges and calacareans, which could explain why molecular phylogenies better reflect traditional glass sponge taxonomy.