MOLECULAR PHYLOGENY OF CALCAREOUS SPONGES USING 18S RRNA AND 28S RRNA SEQUENCES

Abstract

In a recently published work, the phylogeny of Calcispongia was investigated using 18S rRNA data and morphological characters, supporting the monophyly of Calcispongia and their subdivision into Calcaronea and Calcinea, and proposing parsimony-based evolutionary scenarios for a few morphological characters. In a search for a better understanding of body plan evolution in Calcispongia, especially regarding symmetries and the organization of the aquiferous system, the present study analyzes a new dataset of 28S rRNA sequences, alone and in combination with the 18S rRNA data. Independent analyses of the two datasets provide corroboration of the monophyly of Calcispongia, Calcinea and Calcaronea, and of several clades within Calcaronea. The combined analyses of 18S and 28S rRNA provide a better resolution of the phylogeny which leads us to refine hypotheses of morphological character evolution. The asconoid aquiferous system would be primitive for the Calcispongia, with independent acquisitions of the syconoid and leuconoid types within Calcinea and Calcaronea. There is confirmation of the primitive nature of axial symmetry in Calcispongia, with two independent inferred losses, within Calcinea and Calcaronea.