Asplanchna sp. rotifer swimming. Asplanchna rotifers are strong swimmers and feed predatory on other rotifers, ciliates and copepods but are also likely to feed on large algae. The huge, sack-like body of this younger individual is nearly empty, an epiphytic ciliate on the outside below the ciliated corona on the right side can be seen. Microscopic contrast technique : Differential interference contrast. Magnification 90x when printed 10 centimetres wide.