Greek: bounos = little hill; deros = skin protrusion; Latin: inconstans = not stabile. This genus description refers to the fact that these parasites may protrude their anterior end. These trematodes, which parasitize in the intestine of perch, pike, and trout, reach a length of only 4–5 mm, although their operculated eggs are comparably large (100 × 50 μm). Intermediate hosts are mussels and small crustaceans (Cyclops). Diseases occur due to inflammations and necrosis along the intestinal wall. Treatment can be done in aquaria by the water soluble praziquantel product Tremazol® (Fa. Alpha-Biocare, Düsseldorf).