What are Aquatic Animals?
There are many different types of aquatic animals, but they can mainly have a skeletal system or not, so the first classification we will study will be that of vertebrate and invertebrate aquatic animals, and we will find that these are also included in many of the taxonomic categories of the animal kingdom. In addition, it is interesting to know the types of marine animals that exist.
vertebrate aquatic animals
This classification primarily includes fish, but we will also find some reptiles, seabirds and various kinds of mammals.
- Fish
These, in turn, are divided into three classes, depending on their morphology:
- osteichthyes
They are the ones that have a skeleton that calcifies and their gills are protected by an operculum, which is a kind of very hard bone. Within this classification we will find that there is cod, grouper and tuna.
- chondrichthyans
They are fish whose bone system is made up of cartilage and their gills, which are their respiratory system, are exterior and can be seen. Within this group we can find sharks and chimeras.
- Agnathus
These are fish that do not have jaws, such as lampreys.
- reptiles
These are a variety of aquatic animals whose characteristics are that they have scales, their respiratory system is pulmonary and they have a circulatory system through which they are allowed to remain both on land and in water. An example of the reptiles that belong to this group are sea turtles, crocodiles and iguanas, which are an interesting part of the land and water animals.
- Birds
Included in this group are some aquatic birds, such as herons, penguins (which, despite not being able to fly, are still birds), albatrosses, and pelicans. They are identifiable by their feathers, which not only help them fly but also regulate their temperature. Their diet consists of eating other aquatic animals, such as fish and crustaceans. If you'd like to learn more about feathered animals, this is a good example.
- Mammals
There are many classes of aquatic animals included in this classification of mammalian animals and they are mainly:
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- Cetaceans
Although they are mammals, their shape is very similar to that of fish and they have fins. In this group we find whales, dolphins and sperm whales, but there are many more, including species that are part of the marine mammals.
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- pinnipeds
They are mammals that have an elongated body shape that ends in a pair of horizontal fins, as is the case with the walrus, the sea lion, the manatee or the seal, and their diet is also made up of other marine animals, which is why they are carnivores.
invertebrate aquatic animals
The main characteristic of invertebrate aquatic animals is that they do not have an articulated bone system or a backbone. But as there are many aquatic animals that belong to this group, it must be taken into account that there are several classifications of them, which are:
- Cnidarians
They can be free-form or bag-shaped and are made up of more than ten thousand species, all of them aquatic. An example of a cnidarian is the anemone or jellyfish.
- Echinoderms
This class of animals spend their lives exclusively in the aquatic environment, more specifically at the bottom of the seas. Their essential feature is that they are star-shaped and have an amazing ability to regenerate their skin. The best known aquatic animal of the echinoderms is the starfish.
- porifera
Is aquatic animals They can spend their lives in both freshwater and saltwater and live in a gregarious manner, forming colonies that manage to build structures whose function is to filter the water through them in order to obtain their food. They do not have a mouth and their digestion is intracellular.
- marine worms
They have an elongated shape and no limbs. It is astonishing that approximately 90% of the seabed is made up of this class of marine invertebrates, including creeping animals.
- rotifers
They are among the most abundant in water and are microscopic invertebrate living beings that live mainly in fresh water and, to a much lesser extent, in salt water. They have the ability to stick to fungi or lichens in order to survive and there are more than two thousand species.
- Seafood
In this class we can incorporate the arthropods, which are aquatic animals invertebrates that have an exoskeleton or external skeleton, such as crabs, prawns and lobsters. This outer skeleton is made up of a carbohydrate called chitin that hardens, so as they grow, their exoskeleton will change several times.
- Molluscs
Mollusks constitute one of the most extensive phyla of the animal kingdom, because it has been shown that there are more than 100.000 species. Their essential characteristic is that they have very soft bodies, which we can find covered by a shell, but not in all species.
An example of a mollusk with a shell is the snail, but also within these invertebrates we can classify the clam or oysters. Within the group of those without a shell are squids and octopuses.
The case of octopuses is very particular because they have the ability to camouflage themselves to blend in with their surroundings, changing their color and appearance, until they seem to disappear in the seascape. This helps them escape from their predators.
Also particularly noteworthy is the ability of both octopuses and squids to expel ink when threatened, in order to confuse their enemies.
Characteristics of Aquatic Animals
In order to be able to survive in the aquatic environment, aquatic animals have evolved, achieving incredible adaptations, both biological and physical, with which they can make the most of the resources that may be present in their environment and we are going to highlight them separately.
Breathing
It's incredible that there are aquatic animals that can obtain oxygen in two different ways: one is by taking in the oxygen scattered in the water, and the other is by rising to the surface of the water. That's why among aquatic animals we can find three types of respiratory systems: cutaneous, pulmonary, and branchial. If you're interested, you can also read about the types of animal respiration.
The gill respiration system is the one used by animals that have gills, which constitute an organ made up of soft tissues, through which the oxygen that is disseminated in the water can be absorbed. This is the kind of respiratory system that fish have.
The cutaneous respiration system is the one that aquatic animals can carry out through their skin, because it will be the organ that will have the function of exchanging gases in the environment. An example of an aquatic animal that possesses this type of respiration is the starfish.
In the case of the pulmonary breathing system, we will find, as its name indicates, that the breathing process is carried out through the lungs.
This is the respiratory system of aquatic animals that need to rise to the surface to obtain oxygen from the air, as is the case with dolphins and whales, or in the case of animals that do not live in the water but spend a large part of their lives in it, as is the case with birds and mammals that are aquatic. In addition, it is crucial to understand the relationship between animals and their environment, including the aquatic ecosystems.
Food
In principle, we must say that aquatic animals have multiple sources of food, but we can make it clear that phytoplankton is essential in feeding animals that spend their lives in the marine habitat.
Phytoplankton is composed of autotrophic microorganisms, which means that they are capable of synthesizing inorganic material, and are located at the beginning of the food chain of a large extension of the species of aquatic animals, who, in turn, they will constitute the main source of food for other aquatic animals of much larger size.
The interesting thing about the way in which phytoplankton acquires its nutritional properties is that it has the ability to absorb part of the carbon dioxide that is in a free state in the atmosphere and due to this, it carries out two activities that are of the utmost importance.
Indeed, phytoplankton manages to generate oxygen through a process of photosynthesis and becomes one of the main sources of energy in the food chain of aquatic life.
It is also true that the meat of other aquatic animals, as well as plant remains, fruits and seeds are inserted in the food chain of many other aquatic animals, including species of endangered aquatic animals.
Temperature
In this characteristic there are many differences between the different aquatic animals, mostly determined by the type of environment in which they live, since we must not forget that there are some that live in the marine environment, in lakes and in rivers.
In this way, aquatic animals have managed to evolve with regard to the different mechanisms they use to maintain their body temperature, so we will mention them:
Antifreeze
There are aquatic animals that live in very cold waters, such as the fish that live in the seas of the poles, and to regulate their temperature they manage to synthesize proteins that within their organisms have the function of acting as antifreeze.
There are species that carry out this process throughout the year, and others that carry it out only in periods of low temperatures, an example of which is the winter sole.
Scales
It is an external configuration that covers the skin of aquatic animals and has an insulating and protective function, which means that the animals that possess them can fight against low temperatures, such as reptiles and fish.
Feathers or insulating hair
In this case, it is the quantity and distribution of the feathers that helps the birds to keep their body temperature regulated. In the case of animals that have insulating hair, a thick layer of it helps marine animals such as seals to protect themselves from the cold.
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