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Groundwater oligochaetes (Annelida: Clitellata) of the Dinaric region (South-East Europe)

Abstract This work deals with the study of the oligochaete groundwater biodiversity in the Dinaric region, a karstic territory extending along the oriental shores of the Adriatic sea. Historical and new data depict a fauna of 123 species, 36 of which are stygobiotic. About 60% of the stygobionts are endemic to this region. Trichodrilus Claparède (Lumbriculidae) and Rhyacodrilus Bretscher (Rhyacodrilinae, Naididae) appear as highly diversified genera (13 and 10 species respectively); their diversification and radiative evolution in ground waters of the Dinaric region can be in relation with the fresh and stable temperatures in this environment, linked to isolate patches of karst. The presence of Parvidrilidae and Rhyacodriloidinae (Naididae) in this region is specially noteworthy; the parvidrilids are a groundwater Holarctic family present in Alabama (USA) and southern Europe and the rhyacodriloidines are a small Palaearctic group found in Lake Baikal and ground waters of the Limestone Alps (Italy) and the Dinaric karst of Slovenia and Croatia. The Phallodrilinae (Naididae) are represented in the Dinaric region by two species of Spiridion Knöllner and two species of Abyssidrilus Erséus; both these genera seem to be representatives of two ways of colonization of continental ground waters, the former by migration through waters of decreasing salinity, and the later following the Regression model based on sea transgression and regression. Ground waters of the Dinaric region are confirmed as one of the most important hotspots of biodiversity in the world also for the oligochaete fauna.