It is interesting to point out that in this province, as well as in Sicilian and Sardinian ones, the amphipods of the genus Niphargus strongly decrease, and they are gradually replaced by species of the "orcinus" complex, such a diminution being accentuated in the southern Apennines where for the most part populations of Niphargus longicaudatus can be found. The explanation for this southward rarefaction could be related to the greater distance for the origin center of the genus, as well as to the more recent (post-glacial) colonization of the south and insular ground waters of Italy.
The northern part of the province is characterized by less stygobiontes in comparison with the central part, as well as by a high frequency of northern elements, such as gastropods of the genera Avenionia and Pseudavenonia, cyclopid copepods of the "rassenkreise" Diacyclops languidoides, triclad turbellarians of the genus Polycelis, some amphipods of the genus Niphargus, and asellid isopods.
The central Apennines have a rich and diverse invertebrate stygofauna, with a balanced proportion of northern and southern elements; moreover, in this region we can find elements with West-European affinities, such as the gastropod Arganiella pescei that is close to the french species Valvata exilis, species that show trans-adriatic affinities, viz. the amphipods of the "orcinus" complex and other taxa, such as the asellid isopod Proasellus vignai and the cyclopid copepod Graeteriella unisetigera showing affinities with north-west Apennine or Alpine taxa.
This part of the Apennines is characterized by a striking number of endemic or rare species, distributed among the following groups: asellid isopods (Proasellus acutianus, Proasellus adriaticus, Proasellus micropectinatus, Proasellus amiterninus, Proasellus vignai); cyclopid copepods (Eucyclops subterraneus, Acanthocyclops venustus italicus, Diacyclops languidoides aprutinus, Diacyclops languidoides italianus, Diacyclops cristinae, Diacyclops maggii, Diacyclops paolae, Diacyclops paralanguidoides); syncarids (Meridiobathynella rouchi); triclad turbellarians (Dendrocoelum benazzii) and oligochaetes (Frearidrilus pescei, Haber monfalconensis, Haber zavreli and Trichodrilus strandi).
Besides the above groups and species, a most significative feature of this region is the high number of stygobiont harpacticoid copepods, many of them endemic for the central apennines: Nitocrella juturna, Nitocrella achaiae, Nitocrella stammeri, Nitocrella morettii, Parastenocaris pasquinii, Parastenocaris proserpina, Parastenocaris amyclaea, Parastenocaris veneris, Parastenocaris etrusca, Elaphoidella tiberina, Kliopsyllus minutus, Ichnusella pasquinii, Apodopsyllus lynceorum.
The southern part of the province includes a composite stygofauna, that is characteristically very scarce in stygobiontes, some groups, such as the amphipods of the genus Niphargus, the asellid isopods, the gastropods and the triclad turbellarians becoming very rare. On the other hand, some stygophilic and "thalassoid" taxa, as well as some stygobitic species may be found among the copepods (Acanthocyclops agamus, Speocyclops italicus, Diacyclops languidoides nagysalloensis, Pseudectinosoma sp.), the microcerberid isopods (Microcerberus arenicola) and the water mites (Lobohalacarus weberi).
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