The aquatic animals They are those that inhabit the bodies of water of the world, such as seas, oceans, rivers, lakes and ponds. For this they have characteristics that allow them to survive in the particular conditions of a medium composed of water..
Regarding respiration, aquatic animals employ various strategies, such as the gills of fish and other organisms. Another form is pulmonary respiration in marine mammals, or cutaneous diffusion respiration in eels and other species..
Aquatic animals can be classified in different ways, for example by their habitat (marine or freshwater) or by their ability to move. In this case they are called plankton when they are carried away by the current, nekton those that swim and benthos those fixed to the bottom.
However, the most appropriate way to classify the different types of aquatic animals is according to the zoological group to which they belong. Aquatic animals are sponges, cnidarians, echinoderms, crustaceans, fish, most mollusks, partially amphibians, some insects, reptiles, birds and mammals..
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Due to the density of water, aquatic animals can float around, letting themselves be carried away by currents. They can also actively move by swimming, propelling themselves with specialized appendages, either fins or modified legs..
The fins are the most functional adaptation for swimming, since they allow to propel large bodies of water, especially the tail fin. Many bony fish have a specialized tissue in the shape of a bag to accumulate gas and float (swim bladder) and sharks do not have it, they need to keep moving to avoid sinking.
Salinity is a relevant factor in the sea, which is the most extensive aquatic environment on the planet. Aquatic animals that inhabit an environment with a high salt content need to balance their own salt content with the external environment..
If there is a higher concentration of salts inside the body than outside in the water, the water enters swelling it, if it has less, it would come out dehydrating it. Marine aquatic animals have various physiological mechanisms to solve this by maintaining a balance with the environment..
For example, the kidneys expel or retain water to regulate the concentration of salts in the body. Also in some fish the gills have cells that produce chlorine, incorporating chlorides (salts) into the blood and others have a urea content in their blood similar to that in the seawater that surrounds them..
Temperature is another limiting factor in the aquatic environment, varying with both latitude and depth. The further from the equator, the less temperature the body of water will have, as well as the greater the depth..
Similarly, in the case of rivers and lakes, the altitude affects the temperature, since in high mountains the temperature drops. Given this, there are aquatic animals that use physiological mechanisms to maintain their constant temperature despite changes in the environment..
These are homeotherms, like aquatic mammals that use energy to maintain their temperature. Among the strategies used is the dilation of blood vessels to reduce the temperature or contract them to increase it and the development of thick layers of fat and double layer of hair..
Other animals metabolically regulate their temperature, such as tuna, which is capable of raising it 10 ºC above that of the water. They are animals whose internal temperature varies according to the temperature of the water (poikilotherms).
In addition, there are some fish in the Arctic that have special proteins with an anticoagulant function, to avoid freezing at extreme low temperatures.
As depth in a body of water increases, the pressure it exerts on a body increases. In this sense, aquatic animals that inhabit great sea depths have adapted to the increased pressure by developing gelatinous bodies..
On the other hand, the deeper the lower the amount of dissolved oxygen and therefore the animals must be more efficient in the absorption and accumulation of oxygen..
Aquatic animals can breathe through different types of respiration:
This system is highly efficient in absorbing oxygen, which is scarcer in water than in air. The base of this respiratory system are the gills, structures composed of numerous filaments filled with capillaries..
These are small veins through which the blood circulates carrying COtwo waste to exchange it for oxygen (Otwo). The animal sucks in water and it passes through the filaments, absorbing the COtwo and releasing the Otwo what happens to the blood.
Unlike the branchial system, the pulmonary system evolved on land and is adapted to extract oxygen from the air. In such a way that those aquatic animals that use the pulmonary system to breathe, come from ancestors that evolved on land.
These animals are forced to emerge to be able to breathe in the air, since they are unable to extract oxygen from the water. In this case, the respiratory system consists mainly of a pair of sacs (lungs) of specialized tissue where the exchange of O is carried out.two and COtwo.
It is a simple system, consisting of pores and channels that exchange gases through the skin, releasing COtwo and absorbing the Otwo of the water. This type of respiration is carried out by animals with very thin skin such as the electric eel..
Aquatic animals can be classified from many points of view, either by the type of body of water they inhabit or by their mobility. In the first case, there are animals that inhabit rivers and lakes (freshwater) and those that live in the oceans (marine).
While by mobility there are dragged by the currents (plankton), swimmers (nekton) and fixed to the bottom (benthos). However, the most natural way to classify the types of aquatic animals is by their belonging to zoological groups..
Sponges are aquatic animals that are fixed on the seabed without moving (sessile), and filter seawater to obtain food. They are made up of sacs or tubes made up of thousands of cells that form pores in their walls and a large apical opening..
The water enters the pores from where the nutrients are extracted and is then expelled through the upper opening. Currently, about 9,000 species of sponges are recognized in the world.
They group around 10,000 species of corals, jellyfish and hydras, characterized by the presence of cells called cnidocytes, which inject an stinging substance. These organisms have tentacles around the mouth and have two basic shapes, a sessile one called a polyp and a free one called a jellyfish..
They can form colonies like coral reefs or live as separate individuals like jellyfish.
They include some 7,000 species of sea urchins, sea stars, sea cucumbers, ophiuros (sea spiders), daisies and sea lilies. They present a radial symmetry with several arms and in most cases they are mobile, moving either by crawling or even swimming..
They group more than 100,000 species of snails, bivalves (seashells), sea scale insects, squid and octopus. They have a soft body that can be protected by a shell as in bivalves and snails, or naked as in octopus and squid..
Amphibians live between aquatic and terrestrial environments, although some species spend more time of their cycle in one environment than in another. As predominantly aquatic animals, many species of frogs and newts stand out..
It is a group with more than 60,000 species that includes water fleas, barnacles, lobsters, prawns, shrimp and crabs. They are characterized by presenting an exoskeleton or external skeleton made of chitin.
The largest crustacean is the spider crab up to 4 m in diameter and the smallest the water fleas smaller than 3 mm..
Most of the species in this group are terrestrial, however some are mostly aquatic. Of the more than a million species described in the group so far, it is estimated that about 30,000 are aquatic.
Among these there are numerous species of aquatic beetles, as well as hemiptera such as water skaters (guérrido). On the other hand, the larvae of various species of insects develop in water, such as mosquitoes and mayflies..
They are the characteristic group of the aquatic environment, fully adapted to its conditions, with shaped bodies that offer the least resistance when swimming. In addition to lateral fins for its stability and flow to propel itself with force.
Their body is covered with scales that provide protection and insulation, they breathe through gills and regulate their temperature according to the temperature of the water..
There are three main groups, the lampreys and witch fish (agnate) and the sharks, rays and chimeras (cartilaginous). As well as that of the bony fish that are the majority, such as tuna, sardines and horse mackerel.
There are aquatic species such as some snakes, alligators and crocodiles, and various turtles that mostly venture on land, mainly to hatch their eggs. There are more than 60 species of sea snakes, all of them very poisonous.
Birds are mainly terrestrial animals, although some prefer to classify them as airborne animals. However, some species live closely linked to the aquatic environment where they feed.
For example, the Kingfisher and ducks in freshwater bodies, the gull, cormorants, albatrosses and many others in the sea. But of all birds, penguins rank best as aquatic animals, spending much of their life in water..
Despite being the vast majority of land mammals, some species evolved to return to the water from which their ancestors emerged. These are the so-called aquatic mammals, of which the most obvious and well-known are cetaceans..
Among these are the largest animal that inhabits the planet, the whale or blue fin whale. As well as many other fin whales, whales, killer whales, sperm whales, dolphins, dolphins or river dolphins and porpoises.
Cetaceans have fully adapted to the water, transforming their limbs into fins and developing a dorsal opening for breathing. Another group perfectly adapted to the aquatic environment are the seals, sea lions and walruses as well as the so-called sirenians, where manatees and dugongs are found..
But there are other mammals that spend a large part of their life in water, such as otters, hippos, and capybaras..
It is an order of crustaceans whose individuals do not exceed 2 cm in length. Some are herbivores and feed on phytoplankton by filtration from seawater, others are carnivores eating larvae and eggs, but most eat everything (omnivores).
This is the food of large marine mammals, such as the blue whale, and of seabirds such as the penguin. Only the Antarctic krill species (Euphausia superba) reaches a biomass of 379 million tons.
It is the largest animal that exists, reaching up to 30 m in length and more than 100 tons in weight, being hunted to use its oil, liver and meat. This cetacean inhabits all the oceans of the planet and feeds by filtering the water through its baleen to capture tons of krill.
It is another marine cetacean of which several marine and freshwater species are known. They are very intelligent animals that use sound to locate submerged objects in their underwater movements.
There are 34 known species of oceanic dolphins (Delphinidae) that reach between 2 and 8 m long, as well as 7 species of river dolphins (Platanistoideos) that are 1.6 to 2 m long..
With this name, about 29 species of omnivorous fish of the Amphiprioninae family are grouped, which live among the tentacles of anemones. Due to a mucous layer that covers its scales, it does not receive the bites of the anemones, maintaining a symbiotic relationship.
Therefore, both species benefit, the clownfish gain security while cleaning and protecting the anemone from predators.
It is one of the largest marine predators, reaching 5 to 7 m in length, with a jaw with a diameter of up to 1.60 m open. Despite its name, its color is not white except on the belly, its upper part being greyish blue.
This shark inhabits the continental shelf of almost all oceans, except the coldest (Arctic and Antarctic) and feeds on cetaceans, seals, sea turtles, tunas and other large prey.
Octopus is called octopod species, which are soft-bodied aquatic animals (mollusks) and provided with 8 tentacles with suction cups. At the bottom, in the center of the ring of tentacles, they have a mouth or beak, and a rear siphon through which they breathe.
This siphon also expels a jet of water that allows it to travel under propulsion. They are animals of great intelligence and with very good eyesight.
It is one of the 7 species of turtles that inhabit tropical and subtropical seas, and its common name derives from the green color of its fat.
The adults of these aquatic animals feed on sea grasses and lay their buried eggs on sandy beaches. The hatchlings quickly go to the sea at birth.
Coral reefs that develop in shallow, warm waters of tropical and subtropical seas are made up of coral polyps. These are organisms that form colonies of thousands of individuals and are covered with a calcareous outgrowth that forms the reef..
The different colors that corals exhibit are due to algae that grow in symbiosis with them, called zooxanthellae.
This name is applied to a series of species of carnivorous freshwater fish that inhabit the rivers of Central and South America. They are characterized by attacking their prey in groups in a very aggressive way.
The species for which there are reports of attacks on humans are those of the genus Pygocentrus. They have a flattened and compact body with long and sharp teeth, as well as a fast and agitated swim when attacking..
The International Union for Conservation of Nature (IUCN) establishes the red lists worldwide. These lists contain the names of the species that have some degree of threat of extinction, giving them a category according to the level of risk.
It is a fish that can exceed 3 m in length and 400 kg in weight, and inhabits the Atlantic and the Mediterranean Sea. This species is threatened by overfishing worldwide and according to the IUCN it is an endangered species.
This species is a cetacean, a small porpoise that lives in the Gulf of California and of which only about 15 specimens remain. According to the IUCN, the vaquita porpoise is a critically endangered species.
This marine cetacean inhabits the shores of the Mediterranean Sea and the Atlantic coast of North Africa and Portugal. It is estimated that there are only about 630 specimens left, which is why the IUCN lists it as an endangered species.
It is a carnivorous marine mammal that lives in the northern Pacific Ocean, from Japan and Baja California (Mexico). It has legs and is able to go out to the mainland, but spends most of its life in water.
A population of just over 100,000 specimens of sea otter is estimated, and according to the IUCN it is an endangered species.
It is a carnivorous freshwater mammal that lives in the rivers of the Amazon basin and faces a great threat of extinction, since there are only about 5,000 specimens left. According to the IUCN, the giant otter is an endangered species.
Land animals.
Air-ground animals.
Flying animals.
Nocturnal animals.
Diurnal animals.
Animal classification.
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