THACKER, R.W.; ERWIN, P.M.; Univ. of Alabama at Birmingham: Molecular systematics of keratose sponges (orders Dendroceratida, Dictyoceratida, and Verongida): Analyses of 18S rDNA sequences

Traditional systematics of the Demospongiae relies on morphological characteristics, including the presence and arrangement of a diverse variety of siliceous spicules in the mineral skeleton. In the keratose orders Dendroceratida, Dictyoceratida, and Verongida, the mineral skeleton is greatly reduced or absent; these sponges possess spongin fiber skeletons that can display a large amount of phenotypic plasticity. The scarcity of parsimony-informative morphological characteristics has stimulated several debates on the ordinal placement of many keratose sponge taxa, including the families within all three keratose orders. We constructed phylogenies based on 18S nuclear ribosomal DNA sequences to clarify these ordinal placements. Prior to our study, only 3 dictyoceratid, 3 dendroceratid, and 5 verongid 18S sequences had been placed in GenBank; we contributed an additional 16 dictyoceratid, 3 dendroceratid, and 8 verongid sequences. Phylogenetic analyses consistently resolved Verongida as a distinct, monophyletic order, but found Dendroceratida and Dictyoceratida to be paraphyletic groupings. These results suggest that different rates of evolution may occur in these different orders and that the taxonomic status of Dendroceratida and Dictyoceratida may need to be reconsidered. Phylogenies of additional, protein-coding genes may be required to fully resolve relationships within these two orders.