An aquatic respiratory organ is a specialized organ in aquatic animals that allows them to breathe underwater. However, there are several synonyms used to describe these organs in different animals. Gills are the most common respiratory organ in fish, whereas aquatic arthropods like crabs, lobsters, and shrimps use gills as well as branchiostegal lungs or book lungs. In some species of amphibians like frogs and salamanders, the term buccal cavity is used to describe the respiratory organ, while turtles and some aquatic reptiles use lungs modified for underwater breathing. Some marine mammals like whales and dolphins have blowholes for respiratory purposes. Overall, despite the different structures and names of aquatic respiratory organs, they all serve the same critical function.