In this study, we delved into the interaction between corallivorous marine gastropods, the muricid Coralliophilinae Chenu, 1859, and their cnidarian food targets. Coralliophilinae is a subfamily of specialised corallivorous caenogastropods that feed by browsing on octocorals or hexacorals. Only sparse information is available on the phylogenetic relationships and the degree of specificity of the trophic relationships within this corallivorous lineage. To address these gaps, we generated the largest molecular dataset to date, comprising two mitochondrial (cox1 and 16S rDNA) and one nuclear gene (ITS2 rDNA) from 586 specimens collected worldwide. The coral hosts of coralliophilines were identified through an integrative approach, combining literature data with new records, employing morphological and/or molecular markers, and incorporating data from DNA barcoding of the snail stomach content. Our comprehensive approach unveiled the existence of numerous cryptic species in Coralliophilinae, while the phylogeny showed that most of the currently accepted genera are not monophyletic. The molecular dating confirmed the origin of the Coralliophilinae in Middle Eocene, with diversification of most lineages during the Miocene. Our results indicate that the subfamily’s ancestor evolved in shallow waters in association with Scleractinia. Through the evolutionary history of Coralliophilinae, multiple host shifts to other cnidarian orders were observed, not correlated with changes in the depth range. The results of diversification analyses within the subfamily further suggest that the association with the host has influenced the evolutionary patterns of Coralliophilinae, but not vice versa.

Introduction: Host-parasite associations provide very useful models to study adaptive processes. We investigated the interaction between carnivorous marine gastropods, the Ovulidae or egg-cowries, and their cnidarian food targets. Ovulidae (Fleming, 1828), is a family of specialized carnivorous caenogastropods that feed by browsing on octocorals (Anthozoa: Octocorallia: Malacalcyonacea and Scleralcyonacea) or, to a much lesser degree, on antipatharians (Anthozoa: Hexacorallia: Antipatharia) and Stylasteridae (Hydrozoa: Hydroidolina: Anthoathecata). Very scanty information is available on the phylogenetic relationships and the degree of specificity of the relationship with the cnidarians of this corallivorous lineage, especially for deep-water taxa.Methods: To assess taxonomic identifications and investigate cnidarian/ovulid relationships in the context of their evolution, we generated an extensive molecular dataset comprising two mitochondrial (cox1 and 16S rDNA) and one nuclear gene (28S rDNA) from 524 specimens collected worldwide. The coral hosts of the ovulid species have been identified by integrating literature data with new records, employing morphological and/or molecular (the mitochondrial 16S rDNA and mtMSH, and the nuclear ITS2) markers.Results: We obtained a molecular phylogenetic framework for the Ovulidae, time-calibrated with nine reliable fossil records. An ancestral state reconstruction allowed to identify Hexacorallia or Hydroidolina as the most likely ancestral cnidarian host for the Ovulidae.Discussion: Our phylogenetic hypothesis revealed the existence of groups that do not completely correspond to the currently employed subfamilial arrangement. Concerning trophic ecology, while only pediculariines (Pedicularia and allied) are associated with hydrozoans (Stylasteridae), our results suggest that some ovulid lineages shifted independently between octocorals and hexacorals.

The corallivorous snails Coralliophila meyendorffii and its coral host Parazoanthus axinellae are appealing candidates for studying symbiotic interactions at the microbiome level. In this study, we investigated for the first time the microbial community in the stomach of C. meyendorffii and in the polyps of its coral host P. axinellae using as markers multiple regions of the 16S rRNA gene. The bacterial community in the stomach of another corallivorous snail, Babelomurex cariniferus, that feeds on Cladocora hexacorals, was also investigated for comparison. The obtained results indicated the phylum Proteobacteria as the most abundant among the analysed samples, with Alphaproteobacteria and Gammaproteobacteria as the main classes. Among the investigated communities, some bacterial taxa were recognised in line with previous findings in the microbiota of marine invertebrates. As both organisms are exposed to the same bacteria in their habitats, this might suggest shared environmental influences for their microbiota composition. Most of the detected taxa found exclusively or predominantly in P. axinellae samples suggest the presence of holobiont components within the microbial community of this coral, mirroring those identified in other corals, while the stomach microbiome of C. meyendorffii did not indicate a primary role in parasitism. Finally, we provide evidence that many of these bacterial taxa are horizontally transferred between Parazohantus and Corallliophila.

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.

Accurate species delimitation is essential for understanding the evolutionary processes that generate and maintain biodiversity, particularly in marine systems characterized by high connectivity and widespread distributions. Reef-associated fishes of the Indo–West Pacific provide an ideal framework to investigate these dynamics, yet many taxa remain poorly resolved due to morphological conservatism and cryptic diversity. Here, we present a comprehensive molecular assessment of the genus Lethrinus (Teleostei: Lethrinidae), integrating morphological data with mitochondrial markers (COI and Control Region) across 430 specimens spanning the Indo–Pacific, with a focus on the Western Indian Ocean. Using an integrative framework combining species delimitation analyses, genetic distances, and phylogenetic reconstruction, we investigate patterns of lineage diversification and species boundaries within this widespread reef fish lineage. Our results reveal substantial hidden diversity and deep genetic structuring within several nominal species, indicating that species richness in Lethrinus is currently underestimated. In particular, the L. nebulosus complex comprises two highly divergent lineages with distinct geographic distributions, whilst additional cases highlight previously unrecognised evolutionary lineages and range expansions within the south-western Indian Ocean. These patterns suggest that regional environmental factors and oceanographic barriers may play a key role in shaping population structure and diversification across the Indo–West Pacific. Overall, our findings demonstrate that morphology alone is insufficient to resolve species boundaries in this group and that integrative taxonomy approaches are essential for accurate biodiversity assessment. These results have important implications for marine biodiversity monitoring and fisheries management, highlighting the need to incorporate molecular tools into environmental and conservation frameworks in data-deficient regions.