A phylogenomic and morphometric reassessment of Ovulidae highlights host-related shell shape evolution

The egg-cowries comprise a family of specialised carnivorous caenogastropods (Ovulidae Fleming, 1828) that feed by browsing on octocorals, hexacorals and stylasterid hydrozoans. A recent phylogenetic study, employing a Sanger-based multilocus nucleotide dataset, revealed numerous instances of morphological-molecular incongruence and raised the need for a revision of the current classification. To test alternative hypotheses of ovulid classifications, we applied a phylogenomic approach relying on an Exon-capture methodology to 41 samples from 26 genera and 41 species, representative of the subfamily- and genus-level diversity. Tree reconstructions were performed using both Maximum Likelihood and Bayesian inference methods, resulting in a total of five well-supported subfamily-level clades. The genera Jenneria and Pseudocypraea formed a monophyletic clade, sister to Pedicularia, altogether here considered as forming the subfamily Pediculariinae. The monophyly of Ovulinae was upheld, incorporating Quasisimnia. Prionovolvinae as traditionally recognised proved to be a melting pot of diverse genera and species, including Ovula isibasii, challenging conventional morphology-based classifications. To further investigate morphological variation within Ovulidae, we conducted 2D geometric morphometric analyses to assess shape differences. Groups emerging from Principal Component Analysis (PCA) aligned with the traditional, morphology-based classification. The weak phylogenetic signal associated with the morphometric patterns suggested that phylogeny had only a marginal influence on the morphological evolution of this clade, in contrast to the much stronger role played by host adaptation. This phylogenetic reassessment based on robust genomic data, not only helped to refine our taxonomic framework but also underscores the power of molecular insights in investigating complex evolutionary relationships within families such as the Ovulidae. Furthermore, the morphometric multivariate analysis proved efficient in revealing patterns and addressing eco-evolutionary links.