Integrative taxonomy and phylogeny of the siderastreid scleractinian corals

Integrative taxonomy is currently recognised by many as the solution to the “taxonomic crisis”. However, the use of a multi-disciplinary approach to the study of species boundaries in Scleractinia has been, so far, limited. Molecular techniques have provided new opportunities to explore taxonomic boundaries and the phylogeny of taxa traditionally identified according to incongruence of macro-morphological characters of the skeleton and have shown that the traditional coral classification is frequently not congruent with the molecular results. However, skeleton morphology remains the most commonly used tool for the identification of coral taxonomy, is the only link between extant corals and the fossil record, and thus indispensable for reconstruction of the complete scleractinian phylogenetic tree. The family Siderastreidae includes six genera (Siderastrea Blainville, 1830, Psammocora Dana, 1846, Coscinaraea Milne Edwards and Haime, 1848, Anomastraea Marenzeller, 1901, Pseudosiderastrea Yabe and Sugiyama, 1935, and Horastrea Pichon, 1971) grouped together based on frequent presence of synapticulae and the fusion of septa. We re-assessed the taxonomy and phylogeny of the Siderastreidae through a multidisciplinary approach including the morphologic study of the polyp, morphometric analysis of the corallite structures, skeletal microstructures, and the molecular analysis of both a nuclear and a mitochondrial markers. The morpho-molecular study of the Siderastreidae confirmed the partial results previously obtained by other molecular studies indicating that the genera, and some species, currently ascribed to the family belong to different phylogenetic lineages and that commonly used skeletal macro-characters are not necessarily the most informative ones. In particular, the deepest divergence detected separates Pseudosiderastrea and Siderastrea from the remaining genera, and indicates that the genera Psammocora and Coscinaraea are not monophyletic. The re-evaluation of the polyp and skeleton characters and of previously disregarded macro and microstructures have proved phylogenetically informative when combined with molecular results