Sea lamprey (Petromyzon marinus). This is a jawless fish that is a parasite on many other types of fish. It attaches itself my its mouth to the skin of its prey and rasps through it with its rough tongue. It then sucks blood and flesh from its victim. An anticoagulant chemical in its saliva prevents the wound healing. The lamprey drops off its host when it is full or its host has died. It spends much of its life in fresh water. It returns to a river to breed and spends the first few years of its life as a filter-feeding larva in slow-flowing parts of a river.