Rotifer and cyanobacteria. Polarised light micrograph of a rotifer, Ptygura melicerta (centre), amongst filaments of cyanobacteria of the genus Rivularia. Rotifers are common multicellular animals found in pond water. Ptygura melicerta builds a protective tube from its own secretions and surrounding detritus, from which a corona of beating hair-like cilia protrudes, creating a current that sweeps food into the mouth. Cyanobacteria, also known as blue-green algae, are bacteria that obtain their energy through photosynthesis. Magnification: x200 when printed 10 centimetres wide.