Crinoids were very common in warm, shallow seas in the past. Their stems are abundant as fossils around Cincinnati, and entire specimens can sometimes be found in limestones near Brookville Lake. Sea lilies are living crinoids that remain in tropical seas, using their arms to capture plankton for food. Sea stars, while commonly called starfish, are not fish and live in diverse colors and shapes, using tube feet and a water vascular system to feed on bivalve mollusks.