animals that partially or wholly inhabit aquatic habitats
Aquatic is a term often used in biology and ecology. Literally, it means watery, and refers to both fresh and salt-water. So aquatic plants or animals are those that live in water: ponds, rivers, oceans. Aquatic mammals include whales, dolphins, seals, walrus, and also otters, beavers, and other river forms. Aquatic birds are even more numerous: ducks, herons, waders, kingfishers, penguins.