Classification of Animals

We explain how animals are classified, the specific characteristics of vertebrates and invertebrates and various examples.

How are animals classified?

Animals, also called metazoans or members of the animal kingdom (animalia), are multicellular living beings, equipped with their own mobility. and a metabolism based on the biochemical decomposition of organic matter from other living beings. In this they are distinguished, as we know, from plants, immobile and capable of synthesizing their own food from inorganic matter and sunlight.

However, the world of animals is vast and complicated, and humans have been trying to understand it since ancient times. To this end, it has designed numerous classification systems, which throughout history have been perfected, and which today we understand more or less as follows:

Invertebrate animals Strictly speaking, they are those that do not have a vertebral column or skull, although this extends to an articulated internal skeleton. They can have exoskeletons or other forms of support and body defense, however. In general, invertebrates are evolutionarily simpler beings, with soft structures and small size, among which are 95% of known animal species. These include:

• sponges or porifera. These are the simplest animals that exist, which lead a slow, aquatic life on different surfaces of the seabed, filtering the water that passes through their conduits and growing in colonies of more or less identical beings.
• mollusks. Mostly marine creatures, although there are also terrestrial species (such as slugs and snails), they have a soft body that may or may not be covered by a calcareous shell, and may or may not have extremities, such as feet or tentacles. Examples of mollusks are oysters, octopuses, and squid.
• The worms. In this group we can include both annelids (segmented worms, like worms) and worms (flatworms, like flatworms and nematodes), that is, elongated animals without limbs, which live in the environment. or parasitizing other living beings, animals and/or plants.
• echinoderms. Marine animals equipped with a calcareous internal skeleton, whose bodies have pentaradial symmetry and often tentacles (like starfish), or sharp spines (like hedgehogs).
• The arthropods. This is the largest group of animals on the face of the Earth and has conquered absolutely all habitats. They are beings equipped with a chitin exoskeleton, some winged, all equipped with articulated limbs. We are referring to the immense totality of insects, millipedes or centipedes (millipedes and centipedes), crustaceans (crabs, lobsters, prawns) and also arachnids: mites, scorpions and spiders in general.

Vertebrate animals They are those that have a spinal column and a skull, in which a highly developed nervous system is protected, and which is complemented by a more or less articulated endoskeleton. Although they are comparatively a minority of species, they are the most evolutionarily complex and largest, adapted to life on land, water and air. Vertebrates are also often called “cranials” (craniata) and among them are:

• The lampreys. They are animals similar in appearance to eels, but without jaws and scales. They are considered the starting point of current vertebrates, since they do not have vertebrae themselves, but rather similar structures.
• The fish. Both bony and cartilaginous (such as rays and sharks), and both ray-finned and lobe-finned, are the most abundant vertebrates in the sea. Thousands of species of them are known, and they form the bulk of the marine life that humans feed on.
• The amphibians. With terrestrial life but aquatic habits (such as reproduction), these living beings were the first to make the leap from marine to terrestrial life, and today they are located somewhere in between. Frogs, toads, salamanders and other similar amphibians lay their eggs in wells, lakes and rivers, and from them hatchlings with gills and appendages for swimming, which after a metamorphosis will gain lungs and terrestrial limbs.
• The reptiles. Mostly terrestrial animals, with oviparous reproduction and a scaly body, cold blood, these animals once ruled the world. Today they are a diverse group, including turtles, crocodiles, iguanas, snakes and other similar forms of animal life.
• The birds. Evolutionary descendants of the reptiles of yore, birds are the world's largest flying creatures, whose light-boned, cupped bodies are covered in feathers of various colors. Its head has a bony beak for feeding and two legs with claws of different sizes. They can be carnivorous, vegetarian or scavengers, and many of them inhabit the surfaces of seas, rivers and lakes.
• mammals. Characterized by viviparous reproduction and by feeding their young with breast milk, mammals are a group of warm-blooded and extremely diverse animals, which include everything from a giraffe to a lion or a seal, from an ape to an elk. , a dog or a bear, even the human being himself.

Continue with: Classification of the animal kingdom

References

• “Animalia” on Wikipedia.
• “Classification of animals” in Digital Contents of the University of La Punta (Argentina).
• “Animals: classification” in INTAchicos (Argentina).
• “Classification of Animals” (video) in Make It Easy Education.
• “Animal” in The Encyclopaedia Britannica.