What are invertebrate animals?

We explain what invertebrate animals are and how these animals are classified. In addition, examples of invertebrates.

1. What are invertebrate animals?

It is known as invertebrate animals to all the species of the animal kingdom that do not have a notocordio or dorsal cord, nor a spine, nor an articulated internal skeleton. In this set, 95% of the known living species are found, between 1.7 and 1.8 million species (2005 figures).

Invertebrates are also usually smaller, compared to large terrestrial or aquatic vertebrates , and although they lack an articulated skeleton , they often have exoskeletons (such as insects) or shells and shells of resistant substances (such as mollusks) .

This is not a homogeneous group, much less: since the beginning of the term “invertebrate” (from the French animaux sans vertèbres , animals without vertebrae), its creator, the naturalist Jean-Baptiste Lamarck , subdivided them into ten different classes : mollusks, Cirripeda, annelids, crabs, spiders, insects, worms, echinoderms, polyps and infusoria. This classification is no longer used, of course.

The invertebrate group has been difficult to classify and study, given its small size and the diversity of environments they inhabit . In the current classification of zoology , it is estimated that the group is composed of animals of the following edges:

• Arthropods , equipped with exoskeleton and articulated limbs, such as insects, arachnids, crustaceans and myriapods.
• Mollusks , soft and non-segmented body, often covered with shell or shell to defend it.
• Porifers , that is, marine sponges, with bodies endowed with radial symmetry.
• Cnidarians , simple aquatic animals, such as corals and jellyfish.
• Echinoderms , mostly marine, such as sea urchins and starfish.
• Platelmintos , that is, flat worms (in some cases parasites).
• Nematodes , or cylindrical worms.
• Annelids , or earthworms and leeches.

2. Examples of invertebrate animals

Some common examples of invertebrate fauna can be the following:

• Common insects , such as cockroaches, butterflies, moths, beetles, flies, mosquitoes, ants, termites, etc.
• Poisonous arachnids , like most spiders, scorpions or scorpions, centipedes.
• Marine crustaceans , such as lobsters, shrimp, prawns and sea cockroaches.
• Marine mollusks , such as octopus, mussels (and other bivalves), squid, etc.
• Parasitic flatworms , such as tapeworm, the waterworm or the wide fish worm.
• Cnidarians , such as sea anemones, jellyfish, corals and polyps.
• Echinoderms such as starfish, sea urchin, sea lilies, sea cucumbers or sea daisies.
• Cylindrical worms , some parasites such as ascaris lumbricoides or toxocara canis , and others of free and aquatic life.