What structure quickly shoots water out to propel a mollusk forward in water?

The structure that quickly shoots water out to propel a mollusk forward is called the siphon. Mollusks, particularly cephalopods like squids and octopuses, use their siphon to expel water forcefully, creating a jet propulsion mechanism that allows for rapid movement through the water. This method enables them to escape predators and navigate efficiently in their aquatic environments.