Didinium

Didinium is a genus of unicellular ciliates comprising at least ten accepted species, all of them free living carnivores. Most species live in fresh and brackish water, though three marine species are known. Their diet consists largely of the ciliate Paramecium, although Didinium will also attack and consume other ciliates; some species, such as Didinium gargantua, also feed on non ciliate protists including dinoflagellates, cryptomonads and green algae.