NICHOLS, S. A.; University of California, Berkeley: Does the existing classification reflect the relationships within demosponges? A molecular phylogenetic approach.

Demosponges are hypothesized to belong to the most basal metazoan clade. The majority of marine sponges and all freshwater sponges are included in the Demospongia. Despite their importance to our understanding of metazoan evolution and aquatic ecology, we have only a rudimentary knowledge of the internal relationships of major demosponge clades. Sparse knowledge of demosponge phylogeny can be attributed to a dearth of complex morphological characters useful for cladistic analyses. Furthermore, our interpretation of the available characters is often confounded by eco-phenotypic plasticity and suspect homology. The combination of sponge antiquity and morphological simplicity may result in excessive taxonomic �lumping� that could mask early phylogenetic divergences of demosponge lineages. Thus, the existing morphologically-based sponge taxonomy may not accurately reflect relationships in many instances and may underestimate overall biodiversity within the clade. Here, I present a phylogeny of demosponges based upon approximately 900 bp of 28rDNA data. In particular, I examine the position of taxa long considered to belong to the ‘order’ Hadromerida. These data illustrate inconsistencies between phylogeny and taxonomy and address general questions of character homology and demosponge biodiversity.