Steps towards a revision of the Perla bipunctata Pictet, 1833 species complex (Plecoptera: Perlidae)

The traditional view of the species Perla bipunctata Pictet, 1833 and Perla grandis Rambur, 1842 as widely distributed taxa in the West Palaearctic does not stand up to a more thoroughgoing taxonomical examination. In the present study, we demonstrate that these taxa belong to unresolved species complexes, whose members are disjunctly distributed over different, often isolated, geographical areas and mountain ranges. In the first part of this study, based upon the review of specimens labelled Perla bipunctata, Perla grandis and (obsolete) Perla maxima (Scopoli, 1763), collected by the Italian plecopterologists Elisabetta Ravizza Dematteis and Carlalberto Ravizza, between 1970 and 1994 in rivers Nure, Staffora, Stura di Demonte, Stura di Ala, Soana and Tanaro, we show, by a morphological analysis of the penial armature and the sclerotized aedeagus of adult males, that these taxa fall into three distinct groups: a taxon found in the upper course of these rivers, then a second one present in their middle section and finally a third one living only in the very low reaches. The taxonomical problems related to the identification of these three alpine taxa are discussed, and a new species, named Perla ravizzaorum sp. n., is described. This same tripartite species cluster within the Perla grandis / bipunctata species group is then shown to be replicated also in other alpine and perialpine regions, and only in these. Putative specimens of Perla bipunctata or Perla grandis collected in extra-alpine regions, such as the British-Irish Isles, the Pyrenees, the Cantabrian Cordillera, the Baetic System, and North Africa, are established as taxa belonging to different species, which are in need to be re-described and renamed. Two additional new species, Perla andalusiaca sp. n., from Andalusia, and Perla pyrenaica sp. n., from the Pyrenees, are described from adults and nymphs. The species name Perla carlukiana Klapalek, 1907, is finally re-instated for specimens from the British-Irish Isles.