Animal environments are classified as either aquatic (water),
terrestrial (land), or
amphibious (water and land). 'Aquatic animals' require a watery
habitat, but do not necessarily have to live entirely in water. This term can be applied to
aquatic or sea mammals such as those in the order
Cetacea (
whales), which cannot survive on land, as well as four-footed
mammals like the river
otter (
Lutra canadensis) and beavers (family
Castoridae). It also includes aquatic
birds that either swim, wade or dive on the water itself and live outside the water. These include the seabirds, such as gulls (family
Laridae), pelicans (family
Pelecanidae), and albatrosses (family
Diomedeidae), and the anseriforms, such as ducks, swans, and geese (family
Anatidae).Aquatic animals can release nitrongenous wastes as ammonia.
Amphibious and amphibiotic animals, like
frogs (the order
Anura), while they do require water, are separated into their own environmental classification. The majority of amphibians (class
Amphibia) have an aquatic
larval stage, like a
tadpole, but then live as terrestrial adults, and may return to the water to
mate.
Aquatic animals are often of special concern to
conservationists because of the delicacy of their environments.