The genus Mercuria Boeters, 1971 in Morocco: first molecular phylogeny of the genus and description of two new species (Caenogastropoda, Truncatelloidea, Hydrobiidae)

Abstract. The western Palearctic freshwater snail genus Mercuria (Caenogastropoda: Hydrobiidae) comprises 26 species primarily distributed in lowland localities of Western Europe and North Africa. Although this genus in North Africa has received considerable attention in terms of species discoveries through morphological descriptions, its distribution and phylogenetic patterns remain unknown. Based on morphological and mitochondrial DNA (mtCOI) evidence, this study examines the three Mercuria species (M.bakeri, M.tingitana, and M.targouasensis) from Morocco identified so far. Besides expanding on information regarding the anatomy of these species, two new species (M.midarensissp. n. and M.tensiftensissp. n.) are described for this region and phylogenetic relationships inferred between these species and the European M.emiliana and M.similis. All Moroccan and European species were recovered as independent entities according to these phylogenetic inferences (uncorrected p-distances 2.8–8.5%) and DNA barcode data. Moroccan Mercuria species clustered with M.emiliana from Spain, although basal relationships within this clade were not well supported. Given that factors such as the season when specimens are collected, habitat type, and parasites could be responsible for the remarkable intraspecific variation observed in shell and penis morphology, it is proposed that the most efficient approach to delimit and identify Mercuria species is to combine morphological descriptions with genetic data.