Heliozoa in Rio Tinto. Light microscopy footage of Heliozoa, a group of microscopic predatory protozoa also known as sun animalcules. This predator uses its long sticky filaments to move and to catch its zooplankton prey such as Euglenoides (seen at the end of the clip). Heliozoans feed in the same way as amoebas, by engulfing their prey. The Rio Tinto river flows through an area rich in minerals, and contains extremophile bacteria that feed on iron and sulphide minerals, creating an acidic environment. Over many kilometres this river has a pH of 2 and the reddish tint for which it is named. Despite the toxic environment, this river contains many microbe and algae species that are adapted to survive in such conditions.