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, endowed with their own mobility and a metabolism based on the biochemical decomposition of organic matter from other living beings. In this, they differ, as we know, from plants, which are immobile and capable of synthesizing their own food from inorganic matter and sunlight.
However, the animal world is vast and complicated, and humans have been trying to understand it since ancient times. To this end, they have designed numerous classification systems, which have been refined throughout history and which today we understand more or less as follows: You must read about Animal Kingdom once.
Invertebrate animals
Strictly speaking, these are those that do not have a backbone or skull, although this extends to an articulated internal skeleton. They may have exoskeletons or other forms of support and bodily defense. In general, invertebrates are evolutionarily simpler beings, with soft structures and small size, and comprise 95% of known animal species. These include:
- Sponges or poriferans: These are the simplest animals in existence, leading a slow, aquatic life on different surfaces of the seabed, filtering the water that passes through their channels 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 which may or may not have limbs, such as feet or tentacles. Examples of mollusks include oysters, octopuses, and squid.
- Worms: This group includes both annelids (segmented worms, such as earthworms) and worms (flatworms, such as platyhelminthes and nematodes), that is, elongated, limbless animals that live in the environment or parasitize other living beings, both animals and plants.
- Echinoderms: Marine animals with a calcareous internal skeleton, whose bodies display five-pointed radial symmetry and often have tentacles (such as starfish) or sharp spines (such as sea urchins).
- Arthropods: This is the most numerous group of animals on Earth, having conquered absolutely every habitat. They are creatures with a chitinous exoskeleton, some winged, and all with articulated limbs. We are referring to the vast majority of insects, millipedes or centipedes (millipedes and centipedes), crustaceans (crabs, lobsters, shrimp), and also arachnids: mites, scorpions, and spiders in general.
Vertebrate Animals
These are animals that possess a backbone and a skull, which protect a highly developed nervous system and are complemented by a more or less articulated endoskeleton. Although they are a comparative minority of species, they are the most evolutionarily complex and largest, adapted to life on land, water, and in the air. Vertebrates are also often called “cranial” (craniata) and include:
- Lampreys: These are animals similar in appearance to eels, but lack jaws and scales. They are considered the starting point of modern vertebrates, given that they do not actually have vertebrae, but rather similar structures.
- Fish: Both bony and cartilaginous (such as rays and sharks), and both ray-finned and lobe-finned fish, are the most abundant vertebrates in the sea. Thousands of species are known, and they form the bulk of marine life that humans feed on.
- Amphibians: Terrestrial but with aquatic habits (such as reproduction), these living beings were the first to make the leap from marine to terrestrial life, and today they are somewhere in between. Frogs, toads, salamanders, and other similar amphibians lay their eggs in ponds, lakes, and rivers, and from them hatch young with gills and swimming appendages, which after metamorphosis develop lungs and terrestrial limbs.
- Reptiles: Mostly terrestrial, oviparous, scaled, cold-blooded animals, these animals once ruled the world. Today, they are a diverse group that includes turtles, crocodiles, iguanas, snakes, and other similar animal life forms.
- Birds: Evolutionary descendants of ancient reptiles, birds are the world’s largest flying creatures, whose lightweight, hollowed-out bony bodies are covered with feathers of various colors. Their heads feature a bony beak for feeding and two clawed feet of varying length. 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 feeding their young with breast milk, mammals are a group of warm-blooded and extremely diverse animals, which includes everything from a giraffe to a lion or seal, from an ape, a moose, a dog, or a bear, to humans themselves. Maybe you should definitely read about Stalking once.
References
All the information we offer is supported by authoritative and up-to-date bibliographic sources, ensuring reliable content in line with our editorial principles.
- “Animalia” on Wikipedia.
- “Classification of Animals” on Digital Content from the University of La Punta (Argentina).
- “Animals: Classification” on INTAchicos (Argentina).
- “Classification of Animals” (video) on Make It Easy Education.
- “Animal” in The Encyclopaedia Britannica.
