What do Invertebrate Animals Mean?

Invertebrate animals are those that lack a dorsal cord, spine and internal skeleton. That is, they have no bones. Generally, they are small in size and have some kind of protective structure or exoskeleton, such as shells.

According to taxonomic classifications, invertebrates are all those animals that do not fall within the vertebrate subfile, which in turn belongs to the chordated edge of the animal kingdom.

Approximately 95% of the living species known so far, belong to this group, so they represent the greatest biodiversity on the planet.

Due to their small size and in many cases, difficult location, the study of invertebrates was relegated for centuries. It was only in the 18th century that its potential began to be considered in terms of scientific research, mainly due to the interest of French naturalist Jean-Baptiste Lamark, who dedicated himself to the study of invertebrate animals and classified them into 10 groups.

However, advances in zoology allowed us to make a new reclassification, which is the one currently used: arthropods, molluscs, porifers, cnidarians, echinoderms, flatworms, nematodes and annelids.

Types of invertebrate animals


They are invertebrates characterized by the presence of an exoskeleton that change in the growth phase, articulated legs, segmented body in two or three regions, with repetitive patterns.

Arachnids (mites, scorpions and spiders), insects (ants, butterflies), myriapods (such as centipedes) and crustaceans (crabs, shrimp, prawns) belong to this group.

Spiders are invertebrate animals of the arthropod group.


They have a soft body, in some cases protected by a shell. Their bodies are symmetrical and without segmentation.

Clams, octopus, squid and oysters are some representatives of this group.

Octopuses are invertebrates of the group of mollusks.


To this category belongs a group of generally aquatic and sac-shaped invertebrates. Water leaves your body through a large opening in the upper part called “osculum”, and enters through smaller pores located in the walls of your body.

Marine sponges are porous invertebrates.


They are marine invertebrates with a sack-shaped body and have a single opening that serves as a mouth and anus at the same time and usually has one or more tentacles.

Jellyfish, corals and polyps are cnidary invertebrates.

Corals are a type of cnidary invertebrate.


They are marine invertebrates with pentarradial symmetry; This means that they have 5 regions around a central disk. They have an exoskeleton formed by limestone plates that, in some cases, can have spikes.

The stars and sea urchins represent the group of echinoderm invertebrates.

A starfish, belonging to the group of echinoderms.


Also known as flat worms, they are the simplest animals with interneurons. Most are hermaphrodites and have parasitic life forms, so they need one or more guests during their life cycle.

Parasites such as tapeworm are the best known species of flatworms.

Prostheceraeus giesbrechtii, a species of the group of flatworms


Also known as cylindrical or round worms, these invertebrates are characterized by having a body without segmentation, with muscles that allow their movement. Some nematodes are transmitting agents of intestinal diseases.

The Necator americanus is an intestinal parasite, of the group of nematodes, causing a disease called hookworm.

Eophasma jurasicum, a type of nematode invertebrate.


They are invertebrates with the body segmented into rings and with metameria, that is, in each ring certain organs are repeated.

Leeches and earthworms are two kinds of annelids.

Leeches are one of the most common annelid invertebrates.