Patterns of septal biomineralization in Scleractinia compared with their 28S rRNA phylogeny: a dual approach for a new taxonomic framework

A molecular phylogeny of the Scleractinia is reconstructed from approximately 700 nucleotides of the 5'end of the 28S rDNA obtained from 40 species. A comparison of molecular phylogenic trees with biomineralization patterns of coral septa suggests that at least five clades are corroborated by both types of data. Agaricidae and Dendrophylliidae are found to be monophyletic, that is supported by microstructural data. Conversely, Faviidae and Caryophylliidae are found to be paraphyletic: Cladocora should be excluded from the faviids, whereas Eusmilia should be excluded from the caryophylliids. The conclusion is also supported by the positions, sizes and shapes of centres of calcification. The traditional Guyniidae are diphyletic, corroborating Stolarski's hypothesis 'A'. Some results from our most parsimonious trees are not strongly statistically supported but corroborated by other molecular studies and microstructural observations. For example, in the scleractinian phylogenetic tree, there are several lines of evidence (including those from our data) to distinguish a Faviidae-Mussidae lineage and a Dendrophylliidae-Agaricidae-Poritidae-Siderastreidae lineage. From a methodological standpoint, our results suggest that co-ordinated studies creating links between biomineralization patterns and molecular phylogeny may provide an efficient working approach for a re-examination of scleractinian classification. This goal is important because in the evolutionary scheme proposed by Wells that presently remains the basic framework in coral studies, patterns of septal microstructures are involved. Validating from molecular phylogenies a given microstructural character state as a potential synapomorphy for a clade is the only way to include fossils in the coral classification, an approach that should allow the unity of coral classification to be maintained up to the origin of the phylum in the Triassic times.