I thank you for your answer; however I'm searching who eats temnocephalas,not what temnocephala eat. I do think that they should have a natural predator but I did find nothing in literature.
A very interesting question! Unfortunately, I can't remember having read anything about this subject. It depends, of course, of the host of the temnocephala.
The literature on predators of ectoparasites in general is scarce. Some cases are well known. Monogeneans on fish are eaten by cleaner fish. Ticks on cattle are actively eaten by specialized birds. But which predator eats fleas and lice on mammals, apart the host itself?
I have noticed cannibalism in the laboratory. Furthermore, infected crustaceans (in this instance freshwater crabs) climbed out of the water and the parasites became desiccated, they did not survive that.
Have you tried to keep it with fish? I have observed fish pick parasites from other fish in freshwater, even catfish.
my research is actually bibliographical, so I'm not doing experiments. However your suggestion is similar to an idea I had, because in bibliography (like this research by Martìnez-Aquino et al.) there are examples of Raphidascaris inside temnocephalas, and these nematodes are usually parasites of fishes.
Article LOS TEMNOCÉFALOS: simbiontes dulceacuícolas
Dear Mattia, Stuart R. Gelder has done some experiments in our laboratory years ago, and showed that branchiobdelids eat temnocephalids. Obviously, this was an in vitro experiments, but may be of some help: