Molecular taxonomy in 2D: a novel ITS2 rRNA sequence-structure approach guides the description of the oysters' subfamily Saccostreinae and the genus Magallana (Bivalvia: Ostreidae)

Molecular approaches have contributed to a drastic reconsideration of organisms' systematics and evolution especially in some groups of bivalves where high levels of phenotypic plasticity have hampered morphology-based assessments. However, these insights have rarely been integrated into taxonomy and classification due to the challenge of taxon description based on DNA data alone. In this study we used, for the first time, an approach based on ITS2 rRNA sequence-structure for the diagnosis and description of new oyster taxa identified based on multi-locus phylogenetic analyses including new molecular data for Striostrea Vialov, 1936. Phylogenetic analyses and diagnostic ITS2 sequence-structure characters supported Ostreidae Rafinesque, 1815 with four subfamilies: Crassostreinae Scarlato & Starobogatov, 1979 (including Crassostrea Sacco, 1897, Talonostrea Li & Qi, 1994, and Magallana gen. nov.), Saccostreinae subfam. nov. (including Saccostrea Dollfus & Dautzenberg, 1920), Striostreinae Harry, 1985 (including Striostrea) and Ostreinae Rafinesque, 1815 (including the remaining genera). We provide a formal description of the subfamily Saccostreinae subfam. nov. and the genus Magallana gen. nov., a diagnosis for the subfamily Striostreinae, and suggest the reclassification of Striostrea circumpicta (Pilsbry, 1904) and Crassostrea zhanjiangensis Wu, Xiao & Yu, 2013 as Ostrea circumpicta and Talonostrea zhanjiangensis comb. nov., respectively. This study demonstrates the suitability of ITS2 sequence-structure characters for taxonomic diagnosis and description. The advantages of such an approach in the context of DNA taxonomy of cryptic taxa are discussed. (C) 2016 The Linnean Society of London, Zoological Journal of the Linnean Society, 2017