Carabus (Cathoplius) aliai was described as a separate species by Escalera in 1944 but since the 1950-60s it has been considered as a subspecies of Carabus (Cathoplius) stenocephalus Lucas, 1866. This downgrading was adopted after examining only a few specimens, due to their rarity in collections. In recent years, an important population of this taxon was rediscovered in the Tan-Tan area in southern Morocco. By combining field observations with laboratory breeding experiments including hybridization trials, and through the morphological examination of a representative number of individuals, it is confirmed that Carabusaliai is indeed a valid species. Despite close geographic distribution, the morphological and biological characteristics of Carabusaliai and Carabusstenocephalusifniensis Zarco, 1941, its northern substitutive taxon, are very different. Carabusaliai adults are characterized by a smaller size, a slender silhouette, a more brilliant aspect, a narrower pronotum, a coarser elytral sculpture, longer legs, and a wider and a little more curved apex of the median lobe of the aedeagus. Carabusaliai larvae are also characterized by a much smaller size and the Carabusaliai pupa has a narrower thoracic area and a different chaetotaxy compared to that of Carabusstenocephalusifniensis. Contrary to this, Carabusaliai has a life cycle belonging to the annual univoltine winter semelparous type. Moreover, the duration of its development cycle is shorter. Carabusaliai is a sabulicolous steppe-wandering species with an intensive running activity, while Carabusstenocephalusifniensis is a more sedentary taxon. Crossbreeding experiments showed a marked reproductive isolation between Carabusaliai and Carabusstenocephalusifniensis. When F1 hybrids were crossed with one another, a very high mortality rate during embryonic, larval and pupal development was evident and no vital F2 neo-adults were obtained. Morphological and biological differences, together with the reproductive failure in Carabusaliai × Carabusstenocephalusifniensis hybrids, clearly indicate that Carabusaliai is a separate Cathoplius species that is distributed in an area south of the Anti-Atlas chain, from Plage Blanche (Guelmim) to Lemsid and Bou Kra (south of Laâyoune). Carabusaliai is therefore both a Saharan desert endemic and an Atlantic resident. Moreover, it is the southernmost Carabus species of the western Palaearctic region.
Keywords: Atlantic element; Carabus ground beetles; Saharan desert endemism; hybridization; life cycle.