The rotifer is a minute aquatic animal named for an optical illusion - waves of beating cilia on its head appear to be a rotating wheel. The cilia are dual purpose: they propel the swimming rotifer and direct food currents to the mouth. Behind the anterior mouth lies a feeding apparatus unique to rotifers: rigid jaws called trophi are manipulated by and embedded in the mastax - a muscular pharyngeal region between the mouth and esophagus. Trophi suck, grab, or grind food.