Rotifer Floscularia ringens feeding. Its rapidly beating cilia (hair-like structures) bring water that contains food to the rotifer. The “wheel animacules” were first described by Leeuwenhoek (ca.1702); when their cilia beat, they look like they have two wheels spinning on top. They live in reddish-brown tubes made of spherical “bricks.” Differential interference contrast microscopy. Charles Krebs, Issaquah, WA, USA.