Aquatic Animals

We explain what aquatic animals are, what types exist, their characteristics and examples. Also, terrestrial and aerial animals.

aquatic animals
All types of animals live in the aquatic environment.

What are aquatic animals?

Aquatic animals are those animals that live all or most of their life in water whether sweet or salty. They can breathe oxygen dissolved in water (through the gills or skin) or they can breathe it from the air (through the lungs).

The amount of water-dwelling species It is so vast that it has not yet been fully discovered due to the inaccessible depths of the ocean. However, aquatic animals can be categorized in the same way as terrestrial animals (into vertebrates and invertebrates), taking into account the characteristics of the organisms and their adaptation to the aquatic environment.

Types of aquatic animals

aquatic animals mollusks
Mollusks are invertebrates that in some cases are protected by a shell.

Aquatic animals are divided into two large groups according to the internal structure of their organism: vertebrates or invertebrates.

Vertebrate aquatic animals

They are those that have a bone skeleton or a skeleton made up of cartilage, and are classified as:

  • Fish. They are those that breathe through the gills, and are divided into three types:
    • Agnatos They have no jaw, like the river lamprey.
    • Chondrichthyans They have a cartilaginous skeleton, like the shark.
    • Osteichthyans They have an internal bony skeleton, like tuna.
  • Reptiles They are those that have a pulmonary respiratory system, a double-circuit circulatory system and scaly skin. Its reproduction can be oviparous or ovoviviparous. For example, the sea turtle, the sea snake, the marine iguana and the crocodile.
  • Mammals They are those that have a pulmonary respiratory system and are characterized by nursing their young. They are divided into five groups:
    • Cetaceans. Like the whale, the beluga and the dolphin.
    • Pinnipeds. Like the seal, the elephant seal and the walrus.
    • Sirenians Like the manatee and the dugong.
    • Pachyderms Like the rhinoceros and the hippopotamus.
    • Rodents. Like the otter and the capybara.
  • Birds. They are the ones that have plumage all over their body, which allows them to stay dry to be able to fly or to maintain their body temperature. They feed on fish and crustaceans. For example, the penguin, the pelican, the seagull and the heron.
You may be interested:  Snake

Invertebrate aquatic animals

They are those that do not have any type of bone or internal cartilaginous skeleton, and they make up a group of six very different species:

  • The arthropods They are aquatic crustaceans that live in the depths. They usually have a shell, a respiratory system with gills, a complex nervous system and sexual reproduction. For example, crayfish.
  • The mollusks They are aquatic animals that may have an exoskeleton called a shell (for example, the mussel) or may not have an external shell (for example, the octopus). In both cases they have siphons (an anatomical structure that is part of the soft organs) through which filtered water enters and leaves, which makes locomotion, feeding, breathing and reproduction possible.
  • The echinoderms They are those that live both in the depths of the sea and in shallow waters. They have an internal skeleton made up of calcareous plates and ossicles (very small bones), and their organism has radial symmetry. For example, the starfish, the sea urchin and the ophiura.
  • The worms They are marine worms or worms that, according to their anatomical shape, are classified as: “annelids ” (with a ring-shaped segmented body), “nematodes ” (with a cylindrical body) or “flatworms ” (flattened body). They have an elongated and soft build because they do not have a skeleton. Some live as parasites and feed on their victims. An example of annelid worm is the leech.
  • The poriferans Also known as “sponges,” they are those that do not have tissues, nerves, muscles or differentiated organs, and many species have a radially symmetrical anatomy. The irregular shape of the body allows water to flow through its cavities and it is through the absorption of water that they are able to nourish themselves.
  • The coelenterates They are multicellular organisms that have only one opening (called “stomodeum”) for access to a single interior cavity that serves the function of both mouth and anus. Some species live clinging to the corals on the seabed and others float freely. They have a sexual and an asexual reproductive phase. For example, the jellyfish, the coral, the hydra and the polyp.

Characteristics of aquatic animals

aquatic animals dugong lung breathing
Lung-breathing animals like the dugong must rise to the surface.

Aquatic animals have different characteristics, depending on:

  • The type of breathing Because the oxygen dissolved in water has a lower concentration than that present in air, aquatic animals have specialized organs to breathe and make gas exchange possible. They can breathe through:
    • Gills. Like the shark and the manta ray.
    • Fur. Like the sea urchin and the starfish.
    • Lungs. Like the dolphin and the whale.
  • The type of habitat. Aquatic animals cannot live in any type of water. Each species has characteristics that adapt to the environment, which can be:
    • Salt water. The seas and oceans.
    • Fresh water Rivers, lakes and lagoons.
  • The type of feeding. Feeding will depend on the type of habitat.
    • In the salt water seas For example, many marine animals feed on phytoplankton (microscopic-sized plants capable of transforming sunlight into energy).
    • In the rivers or freshwater lakes River salmon, for example, feed on smaller fish, crustaceans and insects. Other species base their diet on seeds and fruits that they find on the shores.
  • The type of reproduction Aquatic animals reproduce in two ways:
    • Sexual It can be oviparous, ovoviparous or viviparous. For example, the turtle, the white shark and the dolphin.
    • Asexual By external fertilization of eggs and sperm that are deposited in the water. For example, the starfish.
  • The type of body temperature Some aquatic animals can acclimatize to the cold temperatures of their habitat thanks to their behavioral thermoregulation system that allows them to adapt to the temperature of the water or also thanks to the scales that cover the dermis.
You may be interested:  Birds of Prey

Examples of aquatic animals

aquatic animals reptile iguana galapagos
The marine iguana, from the Galapagos Islands, is unique in its kind.

Some examples of aquatic animals are:

  • The clam It is a bivalve type mollusk that is protected by a shell, lives buried in sand or mud and can withstand temperatures of up to 5°C. It is one of the animals with the greatest longevity: it can live up to 200 years.
  • The vampire squid It is a mollusk of deep, temperate and tropical waters. It shares similarities with squid and octopus, although instead of expelling ink to confuse its attackers, it exudes a sticky substance that takes about ten minutes to dissolve in water.
  • The dugong It is a sirenian-type mammal that lives in coastal areas of the Indian and Pacific oceans, eastern Africa, southeast Asia and Oceania. It feeds only on algae and can stay under water for more than fifteen minutes without coming out to breathe.
  • The beluga It is a cetacean-type mammal that usually lives in the Arctic. It is distinguished by its white skin, for being very intelligent, sociable and curious. It feeds preferably on fish, although it also hunts shrimp, crabs and squid.
  • The penguin It is a seabird that cannot fly, however, it is a skilled swimmer. It feeds on squid, fish and shrimp. It has excellent eyesight that allows it to see its prey at great distances.
  • The sea serpent It is a cold-blooded reptile, it has scales, a forked-tipped tongue and changes its skin completely regularly (just like the ground snake). It lives in tropical areas of the Pacific, Indonesia and Australia.
  • The marine iguana It is a scaly reptile that lives in the Galapagos Islands (an archipelago in the Pacific Ocean) and, upon reaching adulthood, its dermis takes on a dark green color. Despite its sharp claws and teeth, it is a herbivore. It feeds on algae and aquatic plants, which it can even pluck from rocks.
You may be interested:  Tortoise

land animals

snail terrestrial aquatic animals
Land animals move across land by various means.

land animals They are those that live and move by land, that cannot fly or stay in the water for a long time. They feed on plants and other animals, depending on the habitat in which they live (such as the polar zone, forests, jungles or deserts).

They are classified into vertebrates and invertebrates. Some examples of vertebrate land animals are the giraffe, lion, dog, camel, and horse. Among the invertebrate terrestrial animals, the spider, the grasshopper, the snail and the cockroach stand out.

Continue in: Terrestrial animals

aerial animals

aerial aquatic animals colibri
Many birds, like the hummingbird, are aerial animals.

aerial animals are those that have wings, which allow them to fly and move through the air. This characteristic makes it possible for them to live in different territories that are separated by large distances. They can search for food on land or in water.

They are also classified into vertebrates (such as the hummingbird, from the group of birds, or the bat, from the group of mammals) and invertebrates (such as the bee, from the group of insects).

References

  • «Marine worms» in Nationalgeographic.es
  • «What are examples of aquatic animals» on Quora.com
  • “Aquatic animals” on Wikifaunia.com