Returning to the roots: morphology, molecular phylogeny and classification of the Olivoidea (Gastropoda: Neogastropoda)

Abstract The superfamily Olivoidea is broadly distributed in the world’s oceans mostly in coastal waters at tropical and subtropical latitudes. It encompasses around 30 Recent genera and 460 species. Two families – Olividae and Olivellidae – are classically recognized within the superfamily. Their shell is very characteristic due to the presence of a modified callused anterior end and a fasciole. Prior to the present work, neither the monophyly of the superfamily nor the relationships among its genera had been tested with molecular phylogenetics. Four genetic markers [cytochrome c oxidase subunit I (COI), 16S and 12S rRNA mitochondrial genes, and Histone 3 (H3) nuclear gene] were sequenced for 42 species in 14 genera. Additionally, 18 species were sequenced for COI only. The molecular dataset was supplemented by anatomical and radula data. Our analysis recovered, albeit with weak support, a monophyletic Olivoidea, which in turn includes with 100% support, in addition to traditional olivoideans, representatives of a paraphyletic Pseudolividae. The relationships between the former families and subfamilies are drastically revised and a new classification of the superfamily is here proposed, now including five families: Bellolividae fam. nov., Benthobiidae fam. nov., Olividae, Pseudolividae and Ancillariidae. Within Olividae four subfamilies are recognized, reflecting the high morphological disparity within the family: Olivinae, Olivellinae, Agaroniinae and Calyptolivinae subfam. nov. All the recent genera are discussed and reclassified based on molecular phylogeny and/or morphology and anatomy. The homology of different features of the shells is established for the first time throughout the superfamily, and a refined terminology is proposed. Based on a correlation between anatomical characteristics and shell features and observations of live animals, we make hypotheses on which part of the mantle is responsible for depositing which callused feature of the shell. Our results demonstrate that morphological data alone should be used with caution for phylogenetic reconstructions. For instance, the radula – that is otherwise considered to be of fundamental importance in the taxonomy of Neogastropoda – is extremely variable within the single family Olividae, with a range of variation larger than within the rest of the entire superfamily. In the refined classification, Pseudolividae are nested within Olivoidea, which is partially returning to ‘the roots’, that is to