Ammocoetes are the larval stage of lampreys, a type of jawless fish. They are typically found in freshwater environments, where they live buried in sediment. Ammocoetes have a long, eel-like body and lack the characteristic features of adult lampreys, such as the round mouth with teeth. During their larval stage, ammocoetes filter-feed on organic particles in the water. They can remain in this stage for several years before undergoing metamorphosis into adult lampreys. This transformation allows them to develop the features necessary for their parasitic lifestyle, which includes attaching to other fish to feed on their blood.