Hidden species diversity of Corrosella Boeters, 1970 (Caenogastropoda: Truncatelloidea) in the Moroccan Atlas reveals the ancient biogeographic link between North Africa and Iberia

Despite the high species richness of freshwater gastropods in the western Mediterranean, the evolutionary patterns of the North African taxa are poorly understood. In a recent survey of spring habitats in the Atlas Mountains of Morocco (western Maghreb), we discovered ten snail populations anatomically resembling the genus Corrosella (family Hydrobiidae), which was supposedly endemic to the Iberian Peninsula and southern France. Through morphological and molecular investigations, we assessed the taxonomic status of these populations and their evolutionary origins. Molecular phylogenies based on three gene fragments (COI, 16S rRNA and 28S rRNA) from snails of the newly collected populations and 12 additional congeners distributed across the Iberian Peninsula and southern France clustered together the Moroccan populations within Corrosella in a well-supported clade comprising six putative species: two previously identified as Hydrobia marocana and Pseudamnicola pallaryi and four unknown lineages here described as species new to science. According to a molecular clock analysis calibrated with an external rate, the Moroccan clade originated ca. 7.6 million years ago (Mya) (11–4.5 Mya) and its divergence from the southern Iberia lineages likely occurred 8.4 Mya (12.5–5.5 Mya). This suggests that the biogeography of Corrosella in the western Maghreb has been shaped by old vicariance events likely associated with the Late Miocene-Pliocene geological setting of the region and their interplay with the isolation conditions of springs. Our findings considerably expand knowledge of the diversity and geographic range of Corrosella and provide new insight into faunal relationships between North Africa and Europe.