What are invertebrate animals

what are invertebrate animals

We know that throughout this planet there are millions of animal species. Each of them has different characteristics depending on their origin and morphology. Many people do not know well what are invertebrate animals and why they are classified in this category.

For this reason, we are going to dedicate this article to telling you everything you need to know about what invertebrate animals are, their characteristics and importance.

What are invertebrate animals


Invertebrates are known as all species of the animal kingdom, they do not have a notochord or dorsal chord, or backbone, or articulated internal skeleton. This group contains 95% of known biological species, ranging from 1,7 to 1,8 million.

Invertebrates are also generally smaller than large terrestrial or aquatic vertebrates, and although they lack articulated bones, they often have an exoskeleton (as in insects) or a substance-resistant shell and shell (as in molluscs).

It is not a homogeneous group, far from it: from the term “invertebrates” (from the French animaux sans vertèbres, animals without vertebrae), its creator, the naturalist Jean-Baptiste La Jean-Baptiste Lamarck subdivided them into ten different categories: molluscs, barnacles, annelids, crabs, spiders, insects, worms, echinoderms, polyps and trichomonads. Of course, this classification is no longer used.

This group of invertebrates has been difficult to classify and study due to its small size and diversity of habitats. In the current zoological classification, this group is estimated to consist of animals of the following phyla:

  • arthropods. Equipped with exoskeletons and jointed limbs like insects, arachnids, crustaceans and myriapods.
  • Molluscs. The body is soft and unsegmented, usually covered with a shell or shell to protect it.
  • Porifera. That is, the sponge, the body has radial symmetry.
  • Cnidarians. Simple aquatic animals such as corals and jellyfish.
  • Echinoderm. Mainly marine, such as sea urchins and starfish.
  • Flatworms. That is, flatworms (and in some cases parasites).
  • Nematodes. round worms.
  • annelids. Earthworms and leeches.



As their name suggests, invertebrates do not have a backbone or articulated internal skeleton. Despite its strange structure, These types of organisms make up 95 percent of all living species.. In this classification we find insects, crustaceans, molluscs, worms, sponges or arachnids, among others. Due to this diversity, invertebrates do not have a defined habitat. We can place them in any space or environment, whether by water, air or land.

However, its importance lies in many other aspects. For example, They are responsible for the pollination of flowers and serve as food for other types of animals.thus completing the cycle of life. In addition, they help maintain the quality of the soil, clean the environment due to their decomposition properties and control pests, contributing to the balance of the ecosystem.

examples of invertebrate animals

Some common examples of invertebrates are as follows:

  • Common insects. Such as cockroaches, butterflies, moths, beetles, flies, mosquitoes, ants, termites, etc.
  • poisonous arachnid. Like most spiders, scorpions or scorpions, centipedes.
  • marine crustaceans. Like lobster, shrimp, prawns and sea roaches.
  • marine molluscs. Like octopus, mussels (and other bivalves), squid, etc.
  • parasitic flatworms. Wide worms such as tapeworms, hydatidosis or fish.
  • Cnidarians. Like anemones, jellyfish, corals and polyps.
  • Echinoderms. Like starfish, sea urchins, crinoids, sea cucumbers or sea daisies.
  • Cylindrical worms. Some parasites, such as the roundworm or Toxocara canis, and other aquatic and free-living parasites.

Key features

Invertebrates make up 95% of all existing species today. This classification includes both animals without evolution and animals with a higher degree of evolution.

Most invertebrates are arthropods. in which we can find most of the insects of this animal species representing the group of invertebrates, but within the arthropod invertebrates we can also name: crustaceans, myriads and arachnids.

As we have seen before, within the group of invertebrates we can find other classifications such as arthropods, but also: molluscs, jellyfish, sponges, worms and echinoderms.

Due to the great variety of invertebrates, we can find changes in their function and structure. We can clarify one thing: Insects have a body with a head, thorax, and abdomen. The bodies of arachnids and crustaceans are divided into a cephalothorax and an abdomen. The body of a mollusk is divided into: head, legs, guts and mantle.

Despite the discovery of characteristics shared by all the animals that make up this group, there is still a large part that share some kind of similarity, of which we can say that some have radial symmetry and others have bilateral symmetry, known as radial or bilateral.

Invertebrates are found in all ecosystems, including aquatic ecosystems. Due to the variety of species that make up this animal taxonomy, they can be found in any space, whether in the air or on land, but some are even aquatic.

Relationship with vertebrates

What are the invertebrate animals of the world?

Despite being two clearly and specifically differentiated classifications, there is a connection between them because vertebrates evolved from invertebrates. Well, let's be clear, invertebrates are older and vertebrates formed from them.

In accordance with the goal of all living things, which is to preserve species through reproduction, some invertebrates use song as a first step, attracting. Among them: crickets, cicadas, grasshoppers.

In general, almost all invertebrates have the ability to move, even sponges in the reproductive stage (which are immobile as adults). Therefore, locomotion is a good feature of invertebrates.

Some insects exhibit cyclical growth called metamorphosis. Most of them, represented by insects, undergo dramatic structural and functional changes from birth to adulthood. Specifically, insects exhibit cyclical growth with periods of high activity and rest.

As you can see, invertebrate animals make up the majority of animals on our planet. They are very important for the environment and the human being, although many people do not perceive this importance. I hope that with this information you can learn more about what invertebrate animals are, their characteristics and classification.

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