Systematic and Taxonomic Revision of Ostrea stentina Species Complex (Bivalvia: Ostreidae): New Insights From a Topotype‐Based Integrative Approach

ABSTRACT Cryptic marine species complexes with plastic morphology, shallow divergence, and broad distributions are among the hardest taxonomic problems in zoology. The Ostrea stentina complex, reported across the Atlantic, Mediterranean, and Indo‐Pacific, is a striking example. We present the first topotype‐anchored integrative revision of this complex, combining multilocus data (COI, 16S, H3, ITS2, 28S), morphometric assessment of shell variation, and a global georeferenced synthesis of molecularly validated occurrences. Single‐locus analyses and concatenated mitochondrial phylogenetic inference under maximum likelihood and Bayesian frameworks recover three well‐supported species‐level lineages, whereas the low‐variation nuclear loci show extensive haplotype sharing consistent with shallow divergence. Topotypic evidence demonstrates that Ostrea equestris , encompassing both the amphi‐American and Indo‐Pacific lineages, includes O. aupouria and O. spreta as junior synonyms, whereas Mediterranean topotypes indicate that O. neostentina is a junior synonym of O. stentina . A third Atlantic lineage, clearly distinct from O. stentina , is assigned to Ostrea capsa . Quantitative morphology based on 12 shell traits shows extensive phenotypic overlap and no reliable shell‐based diagnostic characters, explaining the long‐standing instability of names in the group. Anchoring lineages to topotypic material also clarifies biogeographic structure, separating core native ranges from disjunct records likely influenced by human‐mediated dispersal. Beyond resolving a globally distributed oyster complex, our study provides a general framework for tackling cryptic marine invertebrate radiations in which nomenclature, morphology, and geography have become decoupled.