CLASSIFICATION OF ANIMALS: MOST PROMINENT TYPES - BIOLOGY - 2025

The classification of animals responds to different criteria and can be done according to their structure, their diet, their habitat, their evolutionary pattern or their way of reproduction.

These ways of ordering them allow us to know their taxonomy and their location within the food chain. In addition, it facilitates the ordering of the large number of species that exist.

Animals are multicellular and heterotrophic beings that are born after a gestation process of variable duration.

This pregnancy is the consequence of the fertilization of an egg by a sperm.

The animal kingdom is the one with the greatest morphological diversity in nature; They can be microscopic or huge, and inhabit very diverse territories. Hence the importance of a classification.

The 7 most outstanding animal classifications

1- According to whether or not they have a skeleton

This is the most common classification of animals, since it is usually more obvious and simplifies the division process. According to this criterion the animals are divided into:

- Vertebrates

Vertebrate animals are those whose body has bones or cartilage and a backbone.

This bone structure shapes their bodies and protects their internal organs. It also allows them to get up on their feet and move or move.

These animals are normally larger than invertebrates. Vertebrate animals are classified as:

Fish

They are aquatic, they breathe through gills and self-regulate their temperature according to the environment in which they are.

There are multiple species of both saltwater and freshwater fish. Its study is in charge of ichthyology.

Amphibians

Amphibians are classified as multicellular organisms and belong to the class amphibia, which means "both means" in Greek.

They were the first to adapt to living part of their days on earth.

They undergo quite a drastic transformation during their development. For example, they breathe through gills in their larval stage, but as they grow they begin to breathe through the lungs.

They are divided into:

- Anurans, the largest group of amphibians. Composed of toads and frogs, which lack a tail in adulthood and have legs developed for jumping.

- Urodelos, animals with a long body, short legs and an obvious tail. They do not emit sound, their skin is moist, and they have the ability to regenerate their legs and tail. Salamanders, lizards and newts come in here.

The reptiles

They are land animals with cold blood and scaly skin. They were most abundant during the Mesozoic era of the planet.

They are in turn divided into:

- Ophidians, this group of animals is mainly made up of snakes. They have a dorsal chord and bilateral symmetry, an endoskeleton, a three-chamber heart, and a squamous body. They breathe with lungs and their body temperature is variable.

- Chelonians, a group made up of turtles with a wide trunk and a hard shell that protects it. They breathe by the contraction of their abdominal muscles. They do not have teeth, but they do have a horny beak that allows them to nibble at their food.

- Saurians: they are reptiles belonging to two lineages: the lepidosauromorphs (lizards and snakes); and archosauromorphs (crocodiles, dinosaurs and birds).

- Crocodilians: includes 24 species of large and semi-arctic predatory crocodiles. They are characterized by flattened noses and laterally compressed tails. Their eyes, ears and nose are on the top of their head.

The birds

They are oviparous, warm-blooded animals with horny beaks, which stand on their hind limbs.

Their bodies are covered with feathers and their forelimbs are wings that allow them to fly. At least most of them.

The mammals

They are animals that suckle (breasts) and have hair or hair all over their body. Human beings fall into this category.

Mammals are subdivided into:

- Monotremes: they are the most primitive mammals, with some reptilian characteristics, such as oviparous reproduction. In fact, its name refers to another of these reptilian characteristics, such as the presence of a cloaca or hole in which the tracts of the digestive, urinary and reproductive systems converge. In this group are the platypus and echidnas.

- Marsupials: they are mammals that last a short time in the mother's womb and complete their development clinging to the mammary glands that the mother has in her marsupial bag. They are viviparous, have a small skull and their molars are triangular. The females have 3 vaginas and the males, the forked penis.

- Placentals: are those viviparous mammals whose offspring develop for a long time in the mother's womb, feeding through a placenta. They have a brain with large cerebral hemispheres that are connected through a corpus callosum. They have two teething processes; one that they only keep in their infantile (milk) age and another, in which the teeth last until their advanced adulthood.

Invertebrates

Invertebrate animals are those that do not have a skeleton or backbone. To get around, they use muscles instead of bones.

To protect their organs they also find a substitute for bones, which in many cases are shells, carapaces or other hard covers.

A characteristic common to the vast majority of invertebrates is that they reproduce through eggs.

The size of invertebrates is usually smaller than that of vertebrates. Invertebrate animals are classified as:

Sponges

They are primitive animals with a porous body.

They lack specialized organs and their sizes and colors are varied. They are divided into: calcareous, vitreous and demosponges.

Echinoderms

Echinoderms are marine animals with an internal skeleton, of secondary pentaradial symmetry.

Its body is divided into five regions arranged around a central disc, so its head is only differentiated from the rest of the body by the madreporic plate.

They have no heart, and are capable of crawling and swimming.

Jellyfish

Jellyfish are marine animals with a bell-shaped jelly-like body and long tentacles loaded with stinging cells.

They move through the water with rhythmic contractions of their entire body, using the water as a 'propellant'. There are three types of jellyfish: hydromedusas, siphomedusas, and box jellyfish.

Anemones and Corals

They are marine animals with a cylindrical body that are normally found in the sand of the seabed, in rocks and in the shells of crustaceans or mollusks.

Its appearance is very similar to that of a marine plant. It has a primitive nervous system. It reproduces sexually and asexually. Includes hermaphroditic species.

Worms

They are small, elongated animals without obvious limbs (they can have them but very short).

Among the types of worms that exist are: annelids, flatworms, nematodes, nematomorphs, onychophores, ipuncúlids and insect larvae.

Mollusks

They are invertebrate animals that have a soft body, naked or protected by a shell.

In this group you can find clams, oysters, squid, octopus and some sea or land snails.

They are characterized by having: a muscular foot, a calcareous shell (sometimes absent) and a radula made up of rows of curved teeth that serve to feed them.

Arthropods

Arthropods are animals whose body is made up of several segments joined by joints. These segments are repeated throughout the anteroposterior axis and can lead to legs, antennae, jaws, etc.

They have an exoskeleton that they shed from time to time. They are subdivided into:

- Arachnids: they have a body divided into two well differentiated parts. They do not have antennae and may have more than one pair of eyes. They are carnivores, digest their food inside and outside their body, and have two hearts. Spiders, mites, ticks and scorpions are some of the animals that make up this group.

- Crustaceans: they are eminently aquatic animals. They are the only arthropods that have two pairs of antennae. They have an exoskeleton. Some of them are: lobsters, crabs, prawns and barnacles.

- Insects: the most diverse group of animals on the planet. They have two antennae, three pairs of legs, and four wings. They are found in all habitats, including the oceans. They have a pair of compound eyes and, in many cases, three simple ones are added to that eye.

- Myrapods: are those animals with a body divided into two regions; head and a long, segmented trunk with many pairs of legs. In some cases, the legs closest to the head serve as venom-inoculating stingers. Centipedes and millipedes are part of this group of animals.

2- According to their diet

According to what they eat, animals are classified into:

Herbivores

They are the animals whose diet is based almost exclusively on plants and their fruits. However, they can also eat eggs and other animal proteins.

Herbivores are also classified into:

- Ruminants.

- Simple stomach.

- Compound stomach.

Carnivores

They are those animals that eat meat and are also classified as:

- Predatory carnivores

- Scavenger carnivores

Omnivores

Animals that eat both meat and fruits and vegetables are called omnivores.

3- According to their way of moving

Another way in which animals can organize is referred to how they use their lower extremities to move. In this sense, animals are divided into:

Quadrupeds

They are animals that move on all fours.

Bipeds

They are animals that move on two legs.

Crawlers

They are those animals that crawl on their belly on the ground or on the surface of trees and rocks.

4- According to its habitat

According to the natural environment in which animals live and develop, they are divided into:

Terrestrial

As the name implies, they are all animals that live on the earth's surface for most of their lives.

Aquatic

They are animals that live in seas, rivers, lakes or any other body of water.

Flying

Their habitat is aerial because they have the ability to fly.

5- According to their way of reproducing

Another way to classify animals is by the way they reproduce. In that case, the animals are divided into:

Oviparous

They are animals that reproduce by laying eggs, from which a larva or an organism is born that undergoes various changes before becoming an adult animal.

Egg laying can occur before or after fertilization.

Viviparous

In this case, they are animals that are born already developed and without any envelope.

6- According to the temperature of your blood

Although it can be a very simple way to classify animals, it can also be useful in some cases.

According to the temperature of their blood, the animals are divided into:

Cold blood

Within this group are reptiles, fish and amphibians.

Hot blood

Mammals and birds are located here.

7- According to the degree of morphological complexity

This classification is related to aspects such as the number of layers of tissue in which the cells are organized, the arrangement of the parts of their bodies, the presence or absence of body cavities, among other factors.

Parazoans

It refers to sponges, which do not have organs, symmetry, or a defined shape. They are subdivided into:

- Calcareous.

- Demosponges.

- Hexactinellids.

Mesozoa

In the form of worms, Mesozoa lack organs and live parasitically on other animals.

Eumetazoans

They are those that have organs and organ systems, and are divided into animals with:

- Radial symmetry.

- Bilateral symmetry. These include acellomed, coelomed, and pseudocoelomed organisms.

It is important to note that these are some of the most common classifications of animals and that they are not exclusive, but rather that the same animal can belong to different of these categories.

References

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