Outer skeleton. Its functions and characteristics in different animals
When the word "skeleton" sounds, we usually immediatelythere is a bare skull and spine, connected by a multitude of different bones. He really is, but not all the organisms of our planet. Many animals have an external skeleton. How it looks and what functions it performs, you will learn further.
What is the outer skeleton?
Muscles, ligaments and skeleton together formmusculoskeletal system of the body. Thanks to them, everything happens, even the smallest in the effort of movement. The skeleton in this system plays a passive role. It is a framework that serves as a support for muscles and protection for internal organs.
The least common is the hydrostatic skeleton. It is devoid of hard parts and is peculiar only to spineless jellyfish, worms and anemones. The inner, or endoskeleton, is present in all vertebrates. It consists of bones and cartilages, completely covered with body tissues.
The outer skeleton is characteristic mainly forInvertebrates, but may also be present in vertebrates. He does not hide inside the body, but completely or partially covers it from above. Exoskeleton consists of various organic and inorganic compounds, for example, chitin, keratin, limestone, etc.
Not all organisms possess only one kind of "skeleton". Some species have both internal and external skeletons. These animals include turtles and armadillos.
Polyps - one of the most "lazy" creatures onplanet. They chose not to move on their own, but to live by clinging to the seabed, like plants. The solid skeleton does not have only anemia. In others, it is represented by a protein (gorgonian, black coral) or lime (madreporous).
The calcareous outer skeleton is commonly calledcoral. In its small holes are the polyps themselves, connected with each other by a membrane of living tissues. Animals form whole colonies. Together, their exoskeletons form an "underwater forest" or reefs on which entire islands are located.
The main part of the reefs is located in the watersSouth-East Asia. The largest colony in the world is the Great Barrier Reef in Australia. It stretches for 2500 kilometers and holds more than 900 islands.
Molluscs possess one of the most beautiful anda variety of external skeletons. Science knows about two hundred thousand species of these animals, each of which has its own structure. The exoskeleton of most mollusks is represented by a shell. Its composition may include aragonite or conchiolin with impurities of calcite, witherite, calcium carbonate and calcium carbonate.
Some animals have a spiral shell,curls of which are twisted in a circle (cochlea) or in the form of a cone (staircase epitonium). At the wide end is a hole - the mouth. It can be narrow and wide, oval, round or in the form of a long slit.
In the Cipressus or Uzhovok every new curloverlaps the previous one, making the spiral difficult to distinguish, and gives the impression that it is not at all. But the bivalves do not really have it. Their shell consists of two convex symmetrical parts that open and close like a casket.
Skeletons of mollusks are usually not smooth. They are covered with microscopic scales, furrows and bulges. In some species, thorns, keels, ridges and plates from variations of calcium carbonate leave the shells.
The type of arthropod includes crustaceans,insects, arachnids and millipedes. Their body has a clear shape and is divided into segments. In this regard, the outer skeleton of arthropods is very different from the covers of corals and mollusks.
Each segment of their body envelops strong cuticles (sclerites) from chitin and other impurities that are joined together by elastic and flexible membranes, providing mobility to the animal.
Insects have a strong but elastic cuticlerepresents the outer layer of the skeleton. Under it is a layer of hypodermis and basal membranes. It consists of fat-protein complexes that prevent the body from drying out.
The crustaceans of the cuticle are more durable and impregnated with lime, which eventually becomes more and more. In some species, the skeleton can be transparent and soft.
The cuticle contains pigments thatgive the animals a variety of colors. From the top, it is usually covered with scales, outgrowths and hairs (hetoids). Individual members of the veil are equipped with glands that produce poison or odoriferous substances.
Strong outer covers are also found among moredeveloped animals. The outer skeleton of turtles is represented by a shell. He is a reliable protection for the animal, as it can withstand the weight of two hundred times the weight of its owner.
The carapace consists of a thick upper keratinouslayer in the form of tightly fastened scutes and internal bone layer. From the inside, a spine and ribs are attached to them, repeating the arcuate shape of the shell. Part of the skeleton that covers the back is called carapace, and the abdominal shield is called a plastron. All the shields on them grow independently of others and acquire annual rings when the animal falls into winter sleep.
Shells can have different colors and patterns, butbasically their color is disguised as an external environment. In starry turtles the shields are black and convex, with yellow "stars" in the center. In African cynics, it is more reserved and has a monophonic yellowish-brown color.