Gastrotrichs: Gastrotricha

Gastrotrichs glide by beating the hairlike fibers on their bellies and use muscles to change direction while gliding. Sea-dwelling species move toward and along solid objects such as sand or gravel and use sticky tubes to attach to the bottom. Some species use creeping movements like those inchworms make. Most gastrotrichs move away from light.

Gastrotrichs make both sperm and eggs. They place sperm in each other while mating. Fertilization (FUR-teh-lih-ZAY-shun), or the joining of egg and sperm to start development, takes place inside the body, but the embryos, or fertilized eggs, are released and develop outside the body. When they hatch, the young gastrotrichs look like small adults. There is no larva stage. A larva (LAR-vuh) is an animal in an early stage that changes form before becoming an adult.