Revision shock in Pacific oysters taxonomy: the genus Magallana (formerly Crassostrea in part) is well-founded and necessary

Abstract

Abstract The description of the genus Magallana provoked taxonomic ‘revision shock’ among Bayne and colleagues, who criticised: (1) the supporting evidence for this taxonomic change, (2) the procedure used and (3) its impact on the nomenclatural stability of oysters. Here, we demonstrate that the description of the genus Magallana fulfils the norms of taxonomic and indexing revisions, and is well-founded on a scientific basis. The clade named Magallana is supported by a robust phylogeny based on comprehensive taxon sampling, independent datasets and varied analytical methods. A new maximum likelihood phylogenetic analysis of oysters, based on mitochondrial gene order data (representing molecular phenotypes above the sequence level), has provided additional support for this classification. These results are fully consistent with all previously published phylogenetic studies, thus providing an unambiguous indication of the stability of the clade that meets all the currently accepted criteria for naming clades as taxa. We show that, while the criterion of ‘morphological diagnosability’ is not applicable at any level of oyster classification, several striking molecular phenotypes are diagnostic of Magallana, both at the nuclear and the mitochondrial genome level. The classification with three genera Magallana, Crassostrea and Talonostrea reflects the evolutionary diversity of Crassostreinae and is consistent with taxonomic ranking criteria adopted for other oyster subfamilies.