Isopodes aselloïdes stygobies d’Espagne, IV – Stenasellidae: taxonomie, histoire évolutive et biogéographie

The entire family Stenasellidae Dudich, 1924 is composed of ancient stygobitic strains sharing a thalassoid and thermophilic origin. Its presence in Europe is dependent on two factors, the permanent existence of emerged continental shields during long geological periods (at least Tertiary + Quaternary), and its conservation in favourable areas during the different glacial crises. The iberian peninsula seems to have been the most suitable european region for the survival of this stygofauna. Some 119 samples from 116 different localities -scattered over 19 Spanish provinces- have been studied. All aquitanian and iberian stenasellids belong to the traditional genus Stenasellus Dollfus, 1897. We must notice that the stenasellids seem to be absent in the betic region as well as in coastal North Africa, lending to the conclusion that the continental evolutive histories of the ibero-aquitanian and of the West African strains are entirely independent. Two multispecific lineages are recognised in the ibero-aquitanian region: an Atlantic strain ( S. breuili group), restricted to the iberian Meseta shield, and a tyrrhenian one (S. virei group), typically limited to the early Tertiary shield Catalonia-Corbières- Corsica-Sardinia. In each strain, we can note the existence of two types of forms: one being rather ancient, endemic, and stenotope, the other more recent, rather interstitial, eurytope and very expansive. Consequently, the original distribution areas of the two strains grew secondarily, with the active colonisation of the alluvial channels of four large hydrographic systems: the Ebro, the Douro and the Garonne-Dordogne systems for the ‘virei’ group, the Guadalquivir system for the ‘breuili’ ’ group. ously responsible for these secondary expansions. This explains, for example, the presence of The quaternary phases of coarse alluvial deposition that followed each low sea-level glacial phase are obvi- Stenasellus virei nobrei in the lower basin of the Douro River basin, far away from the middle Ebro settlement. These expansions seem to be responsible for the differentiation of non-contemporaneous geographical forms inside the ‘virei’ phyletic cluster, some at the level of independent species, some others as subspecies. So, it would be appropriate to consider Stenasellus virei Dollfus, 1897 the status of a superspecies, two endemic new forms of which: S. virei margalefi and S. virei rouchi, are described herein.