Lampreys are jawless fish that belong to the class Petromyzontida. They have elongated, eel-like bodies and a distinctive round mouth filled with sharp, tooth-like structures. Lampreys are found in both freshwater and saltwater environments and are known for their parasitic behavior, attaching to other fish to feed on their blood and bodily fluids. These creatures have a unique life cycle, starting as larvae called ammocoetes, which live in sediment for several years before transforming into adults. Lampreys play a significant role in their ecosystems, but some species are considered invasive and can harm local fish populations.