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The European Alps support several ground beetle Nebria (Nebriola) species, which are morphologically similar. A study conducted on a Nebriola population located between the Eastern Pennine and Western Lepontine Italian Alps revealed the presence of two species, Nebria (Nebriola) cordicollis and N. (Nebriola) gosteliae, and some individuals that possibly represented an unknown taxonomic unit (UTU). Therefore, to further elucidate and characterise the morphological units at the site, we completed a comparative analysis using geometric morphometrics applying the semilandmarks approach. We examined the pronotum, the right elytron, and the median lobe of aedeagus. The quantitative analysis evaluated the overall variation in shape and size of the three structures. Results supported the hypothesised presence of three distinct groups of individuals, with different morphologies for the anatomical traits examined. The pronotum and median lobe of aedeagus exhibited more marked differences among the groups, while the right elytron showed reduced differentiation. These results confirmed that the three groups were separate taxa, and were therefore correctly classified. Based on our findings, we considered the UTU a new species, which is here described as Nebria (Nebriola) casalei sp. nov.

The European Alps support several ground beetle Nebria (Nebriola) species, which are morphologically similar. A study conducted on a Nebriola population located between the Eastern Pennine and Western Lepontine Italian Alps revealed the presence of two species, Nebria (Nebriola) cordicollis and N. (Nebriola) gosteliae, and some individuals that possibly represented an unknown taxonomic unit (UTU). Therefore, to further elucidate and characterise the morphological units at the site, we completed a comparative analysis using geometric morphometrics applying the semilandmarks approach. We examined the pronotum, the right elytron, and the median lobe of aedeagus. The quantitative analysis evaluated the overall variation in shape and size of the three structures. Results supported the hypothesised presence of three distinct groups of individuals, with different morphologies for the anatomical traits examined. The pronotum and median lobe of aedeagus exhibited more marked differences among the groups, while the right elytron showed reduced differentiation. These results confirmed that the three groups were separate taxa, and were therefore correctly classified. Based on our findings, we considered the UTU a new species, which is here described as Nebria (Nebriola) casalei sp. nov.