Evolution is part of the daily life of living beings and the exoskeleton is the result of it. Animals with exoskeleton have a kind of armor that is responsible for covering and protecting the animal's body, a point in favor for these animals and their survival. If you want to know more about it, I invite you to continue reading the following article.
What is the Exoskeleton?
The body of animals is not a mystery to us, we know that they have a skeleton, with vital organs such as: the brain, the stomach, the heart, among others. They also have a dermis that is characterized by being variable and organs through which their five senses will manifest, including other characteristics. But when we talk about the exoskeleton we mean that it is an external structure that is responsible for covering the entire body of different types of animals, including arthropods.
This exoskeleton is characterized by being highly resistant but very malleable, it is in turn made up of different substances. This will depend on the subphylum to which the animal belongs. In the case of insects or fungi, this substance will be chitin, calcium for molluscs and corals. Or in the case of silicas, the substance will be diatoms together with other elements. The exoskeleton is the result of the evolution of living beings, this is because living beings have adapted over the years in order to survive and reproduce.
Animals with Exoskeleton
When we talk about an individual that goes from being unicellular to multicellular, it will go through a series of circumstances in which it will be given support or support. It will allow you to preserve the structure of that particular group of cells. It is from this set or group of cells that the tissues are formed, who are the ones that make up the body. Due to this, in animals the skeleton usually appears together with the musculature as a kind of fastening system, so that this union problem can be solved in this way.
For this reason and thanks to the evolution of all living beings over the years, they have been exposed to various adaptations. This occurs with the objective that success can be achieved in terms of reproduction and survival in all living beings. When we talk about the skeleton, there are going to be 2 types that are going to be fundamental, this is going to be related to its location in the body of the living being.
That is why the exoskeleton or external skeleton can be defined as the one that is covering the body completely. The primary function of this type of skeleton is protection, another no less important function is that it will serve as a support. As for the interior of the exoskeleton, its musculature will be inserted, which will generally originate from the integumentary.
The exoskeleton is present in some living beings, such as certain protists. And even in several rows of animals that are appreciated as invertebrates or lacking a backbone. The exoskeleton, having rigidity in its characteristics and due to its composition, will limit the development of the animal. For this reason, animals with exoskeletons will generally be small, their size will be reduced.
Diversity of Invertebrates with Exoskeleton
Animals with exoskeleton can be found within the group of invertebrate animals. Even when these animals completely lack the entire skeletal structure. In this way, we can group animals with this peculiar characteristic. As an example of those animals with a protective exoskeleton we can name; some sponges of the Porifera phylum, some corals of the Cnidaria phylum, the bryozoans of the Bryozoa phylum, the brachiopods of the Brachiopoda phylum. We can also find some types of molluscs, but above all in all arthropods.
In the case of sponges, even when their skeletal spicules are located in the internal part of the animal. There are some exceptions where these skeletal spicules can be found on the outside of the poriferous body. This peculiarity gives it the characteristics of greater rigidity and even hardness. Various studies currently carried out have shown that some types of sponge such as Hemimycale columella, the protective exoskeleton is going to be thanks to the secretion of bacteria that live in symbiosis with them.
Some researchers take into account some polychaetes, belonging to the Annelida phylum with exoskeleton. But this decision has caused great controversy since the exoskeleton itself is not created by the animal, but is the product of certain mixtures given by joining the grains of sand or mud. Then later this mixture hardens, causing improvements in worm protection. Due to this, this type of species is not considered within the group of animals with an exoskeleton.
https://www.youtube.com/watch?v=F71hwss4DE8
Composition of the Exoskeleton of Invertebrates
As within the group of invertebrate animals it is so varied, since they come from different evolutionary lines, the composition of the exoskeleton of each of these species will change according to each one. This composition can be given by organic or mineral compounds. This will allow a higher state of rigidity or maybe less, since some of them are much softer. But there may be cases where the exoskeleton of others can become stony. Therefore, it would not be uncommon to find invertebrate exoskeletons with a calcium, chitinous or even silica nature as their first compositional compounds.
Exoskeleton of invertebrates of the phylum Cnidaria
Within the Cnidaria family there are some corals that have an exoskeleton, which is composed of calcium carbonate. This species we are talking about are those stony corals of the order Scleractinia which belongs to the class of Anthozoa. This external skeleton is going to be generated in the epidermis of this invertebrate animal. In addition, it will present as its main function the protection of the entire group of corals. In another species of cnidarians, such as those that belong to the class of Hydrozoa, especially to the order of Anthoathecata, the exoskeleton is made up of chitinous. And it will only cover the basal part of said animal.
Exoskeleton of Brachiopod Invertebrates and Molluscs
In some species of invertebrate animals, the structure that forms the exoskeleton is going to be in the form of a protective shell. This peculiar characteristic can be observed in those animals belonging to the Brachiopoda and Mollusca row. However, an important fact to keep in mind is that not all specimens have it.
In the exoskeleton of those invertebrates that belong to the phyllum Brachiopoda, the valves of this structure may be of calcareous origin. They can also be found composed of calcium phosphate with chitin or it can even be calcareous with a little magnesium. On the other hand, the exoskeleton of certain molluscs, including bivalves, is made up of calcium carbonate. Specifically in this phyllum there is a wide variety of shapes, thicknesses, designs and even colors.
Exoskeleton of Arthropod-Type Invertebrates
When we talk about the exoskeleton of those invertebrate animals, specifically arthropods, it is made up of an aggregate which is a polysaccharide that is characterized by being very rigid. Due to this important characteristic, it will grant certain protection to this type of animal. Besides, it also gives it agility and malleability, which allows this type of animal to perform any type of movement, including flight.
The external skeleton of this type of animal will present a peculiarity, since it is articulated and is structured in various layers or plates. It is also possible that it is fragmented and that these are held together by certain flexible membranes. As for its hard regions, they will be known as sclerites.
Invertebrate animals with exoskeletons, specifically arthropods, have generated their great variability and evolutionary achievement. However, this tends to develop a certain disadvantage, and that is that it restricts its size. Due to this particularity, arthropods are smaller in size and in order for them to grow and develop they must go through a process known as “molting”.
With this we refer to the voluntary loss of the "shell", in order to develop correctly, it is a complex process that will require a lot of energy from the animal. Also, during this state, the animal is left vulnerable. In the following video you will be able to observe how the process of “molting” is:
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