Aquatic animal

An aquatic animal is an

animal

, either vertebrate or invertebrate, which lives in the water for most or all of its lifetime. Many insects such as

mosquito

es,

mayflies

,

dragonflies

and

caddisflies

have aquatic larvae, with winged adults. Aquatic animals may breathe air or extract oxygen that dissolved in water through specialised organs called

gills

, or directly through the skin.

Natural environment

s and the animals that live in them can be categorized as aquatic (water) or terrestrial (land). This designation is polyphyletic.

Description

The term aquatic can be applied to animals that live in either fresh water or

salt water

. However, the adjective marine is most commonly used for animals that live in saltwater, i.e. in oceans, seas, etc.

Aquatic animals (especially freshwater animals) are often of special concern to conservationists because of the fragility of their environments. Aquatic animals are subject to pressure from overfishing, destructive fishing, marine pollution and climate change. Many habitats are at risk which puts aquatic animals at risk as well. Aquatic animals play an important role in the world. The biodiversity of aquatic animals provide food, energy, and even jobs.

Air-breathing aquatic animal

In addition to water breathing animals, e.g., fish, most mollusks etc., the term "aquatic animal" can be applied to air-breathing aquatic or sea mammals such as those in the orders

Cetacea

(

whale

s) and

Sirenia

(sea cows), which cannot survive on land, as well as the pinnipeds (true seals, eared seals, and the walrus). The term "aquatic mammal" is also applied to four-footed mammals like the river otter (''Lontra canadensis'') and beavers (family Castoridae), although these are technically amphibious or semiaquatic. There are up to one million types of aquatic animals and aquatic species.

Amphibians, like

frog

s (the order

Anura

), while requiring 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

.

Certain

fish

also evolved to breathe air to survive oxygen-deprived water, such as ''

Arapaima

'' (family Osteoglossidae) and walking catfish.

Most mollusks have gills, while some fresh water ones have a

lung

instead (e.g. ''Planorbidae'') and some amphibious ones have both (e.g. ''Ampullariidae''). Many species of aquatic animals lack a backbone or are invertebrates.

Importance on environment

Aquatic animals play an important role on the environment as well as human's daily usage. The importance of aquatic animals comes from the fact that they are organisms that provide us with sources such as medicine, food, energy shelter, and raw materials that are used on a humans's daily life.

Each aquatic species plays a different role to help us make every day easier, healthier, and also more productive. They also help with the atmospheric pressure and global climate change.

See also

* Aquatic mammal
* Aquatic plant
* Freshwater snail
* List of semiaquatic tetrapods
* Marine biology
* Marine invertebrates
* Marine mammal

References

{{DEFAULTSORT:Aquatic Animal

Animals by adaptation