A molecular phylogeny for the order Clathrinida rekindles and refines Haeckel's taxonomic proposal for calcareous sponges.

Most biological groups are still longing for a phylogenetically sound taxonomic organization. In this article, we aimed to verify the consistency of morphological characters in calcarean sponges of the well-known non-monophyletic order Clathrinida using a molecular phylogeny. For this we included 50 species, including six type species, currently assigned to eight different genera. A maximum likelihood topology was generated for the nuclear ITS marker using the General Time Reversible model and the bootstrap reliability test. Our topology indicated 10 clathrinid clades that included species with consistent morphological characters. In the present study, we defined nine of these clades as clathrinid genera, including four newly described and two newly diagnosed genera. Recent studies have indicated that not much phylogenetic information may be found in morphology, but our findings contradict this general assertion. Our study confirms the suitability of skeleton and body anastomosis as valid characters in a phylogenetically sound taxonomy for the order. Interestingly, we have also found that, apart from the Calcinea/Calcaronea split and a few minor details, Haeckel's original proposal is remarkably similar to our own, which was based on a molecular phylogeny 140 years later.