Turbellaria is a class in the phylum Platyhelminthes (flatworms). They are dorsoventrally flattened and have a simple nervous system concentrated at the head end. They separated from the evolutionary tree quite early, so most of the species do not have an anus, developed breathing system (they breathe through their skin) nor a vascular system.
In the Croatian underground, there are Turbellaria from orders Temnocephala and Tricladida.
Five species belonging to the Scutariellidae family (order Temnocephala) have been recorded in Croatia so far. Four species live on the shrimp from the genus Troglocaris, where some feed on smaller water species, while others live as ectoparasites. Only the species Stygodyticola hadzii was recorded living on an amphipod from genus Niphargus. It is interesting that, from five species discovered so far, three have been described from Croatia (Bubalocerus sketi, B. undulatus and Troglocaridicola istriana) and all three species are stigobiotic.
Temnocephala is a poorly-researched group of animals and it is assumed that there is potential for discovering new species for science in the Croatian underground.
In the first half of the 20th century, three species from order Tricladida (Dendrocoelum subterraneum, D. plesiophthalmum and Dugesia absoloni) were recorded in Croatia. It is considered that D. subterraneum and D. absoloni are troglobionts, but species were not found for a long time after description and their ecological and taxonomic status was questionable. However, recent research has found a stigobiotic species from the genus Dendrocoelum in the Žumberak area and other Tricladida specimens were discovered at other localities. Analysis of those specimens is underway.
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