Molecular identification of the edible rock scallop, <i>Spondylus limbatus</i> (Bivalvia: Spondylidae) from the southwestern Gulf of California

The genus Spondylus is of great economic and ecological importance in the Eastern Pacific; however, its taxonomy has historically been complex due to the phenotypic plasticity in shells and cryptic species. This study addresses this problem through an integrative approach, combining morphological and molecular tools to analyse specimens from the southwestern Gulf of California. The markers (28S rRNA and 16S rRNA) were analysed in individuals of S. limbatus. Phylogenetic results, obtained using maximum likelihood and Bayesian Inference, confirmed the monophyly of the genus and the identity of S. limbatus as a robust and distinct clade. Interspecific genetic distances ranged from 2.5–3.4% (28S rRNA) to 7.6–15.7% (16S rRNA), while intraspecific variability was non-existent (0.0%) for the evaluated markers, reinforcing the stability of these genes for diagnosis. Unlike external ornamentation, which can disappear in adults or be masked by epibionts, constant internal characteristics were identified: an internal purple band and a finely crenulated margin. The study highlights that, given morphological ambiguity induced by environmental factors, the provided DNA sequences – the first 28S rRNA and 16S rRNA sequences for this species – are critical for population monitoring, fisheries management and conservation, raising the total number of species in the genus with global molecular data to 15%.