Exoskeleton: everything you need to know

animals with exoskeleton

The animal kingdom is made up of many types of living beings. There are numerous structures, some more curious than others, that have vital functions for some organisms. One of them is the exoskeleton. It is a structure mainly to support many animals such as crustaceans.

In this article we are going to tell you what an exoskeleton is, what its characteristics and importance are.

What is an exoskeleton and its characteristics

exoskeleton in animals

The exoskeleton is a hard external structure that some animals have to provide protection and support. Unlike humans and other animals that have an internal skeleton, these organisms they have developed a tough outer covering that wraps around their body.

The exoskeleton is composed mainly of a material called chitin, which is a hard and flexible substance at the same time. This chitin provides excellent strength and rigidity to the exoskeleton, allowing animals to use it as protective armor against injury and predators.

One of the most prominent features of the exoskeleton is its ability to grow and moult. As the animal grows, the exoskeleton it becomes too small and restrictive, so the animal sheds it in a process known as molting. Once the old exoskeleton has been shed, the organism secretes a new shell that hardens and becomes its new exoskeleton, allowing it to grow smoothly.

The exoskeleton also plays an important role in the locomotion of these animals. Being a rigid structure, it provides a solid anchor point for the muscles, allowing greater control and strength in movements. In addition, it can also have special characteristics adapted to the specific needs of the animal, such as spines, spikes or protuberances that can serve for defense, camouflage or attracting mates.

While the exoskeleton provides many advantages, it also has some limitations. Being an external structure, it can limit the growth of the animal and restrict its flexibility. Also, it does not provide complete protection against all types of predators, as some animals can find ways to get past or penetrate this outer layer.

diversity and composition


Exoskeletons can be found in various types of invertebrates, although some of these animals have no bone structure at all. Thus, we can mention the following invertebrates as examples of animals with a protective exoskeleton: some sponges, corals, bryozoans, brachiopods, various mollusks, and all arthropods.

In sponges, while their skeletal spicules are usually located within the animal, in some cases they can move outside of the porous animal's body, making it stiffer and stiffer. Recent research has found that in some sponges, such as Hemimycale columella, the protective mineral exoskeleton is secreted by bacteria that live with it.

Some authors also consider some polychaetes with exoskeletons, but this is controversial because in some cases the exoskeleton is not produced by the animal, but is an epidermis attached to grains of sand or mud produced by secretions, which they harden the cuticle and improve the protective conditions of the worm.

Since invertebrates are a diverse group of animals from different evolutionary lines, the composition of the exoskeleton of each of them varies from one type to another, it can consist of organic and/or mineral compounds that make them more or less rigid. , as some are soft while others can become rigid. Thus, we can find exoskeletons of calcareous, chitinous or siliceous invertebrates as the main variants of composition.

Exoskeleton in cnidarians, molluscs and arthropods

Within the Cnidaria phylum, some corals have an exoskeleton made of calcium carbonate, like stony corals. This external skeleton is produced in the epidermal layer of the invertebrate, and its main function is to protect the entire coral colony.

In some invertebrates, the exoskeleton develops into a protective shell, as is the case of animals belonging to the group of brachiopods and mollusks, although not all specimens have it.

In the exoskeletons of brachiopod invertebrates, shell valves may be calcareous, possibly made of calcium phosphate and chitin, or calcium and some magnesium; (eg bivalves) exoskeletons are made of calcium carbonate and come in a variety of shapes, thicknesses, designs, and colors within this phylum.

In the case of the exoskeleton of arthropod invertebrates, the exoskeleton is formed by a compound called chitin, which is a fairly hard polysaccharide that provides protection to this type of animal, and in turn, gives them lightness and flexibility and various actions, including flying. .

A characteristic of the arthropod exoskeleton is that it is articulated and divided into several plates or fragments connected by flexible membranes. The rigid regions are called ossicles.

In arthropods it allows great variability and evolutionary success, however, It also has the disadvantage that it limits the possible size, for this reason, arthropods are small in size and for their growth and development, they have to resort to molting.

Examples of animals with an exoskeleton

molt of the cicada


They are parasitic arachnids of other animals. There are terrestrial and aquatic species, and their diets are varied: bloodthirsty, scavengers and herbivores. Different species can spread diseases or become pests of plants.


There are many kinds of crabs, but in general we are talking about five-legged crustaceans that have a strong shell and claws to protect themselves and catch their prey. They live at the bottom of the sea, forage for food on foot, and consist mainly of smaller animals.


Bees are insects that are widely distributed on earth. They are organized in groups with a well-defined hierarchy. and are important in the pollination process of thousands of plant species.


There are more than 3.000 species of arthropods that are characterized by having elongated bodies divided into segments, multiple legs, antennae, and powerful jaws. They are carnivorous and feed on insects, worms, and snails.

sea ​​spider

They have eight legs for locomotion, so they are compared to terrestrial spiders. They easily blend in with the ocean floor and have long, slender limbs.

I hope that with this information you can learn more about the exoskeleton and its characteristics.

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