Hydras are freshwater relatives of saltwater anemones and corals that live in the open sea. Their bodies are tubular, translucent, and may vary in color. Hydras attach to rocks by a single foot on one end. The other end has a small opening, which can ingest nutrients and expel wastes, surrounded by many stinging tentacles. The tentacles are used in a variety of ways to stun, capture, and maneuver prey. Because their bodies are very elastic, hydras can catch and eat animals much larger than themselves.