When the word "skeleton" sounds, we usually immediately see a naked skull and spine connected by many different bones. He really is, but not all organisms on our planet. Many animals have an external skeleton. You will find out what it looks like and what functions it performs.
What is the outer skeleton?
Muscles, ligaments and skeleton together form the musculoskeletal system of the body. Thanks to them, everything happens, even the smallest in terms of effort. The skeleton in this system plays a passive role. This is a framework that serves as a support for muscles and protection for internal organs.
It happens:
- interior;
- external;
- hydrostatic.
The least common hydrostatic skeleton. It is devoid of hard parts and is peculiar only to soft-bodied jellyfish, worms and sea anemones. All vertebrates have an internal or endoskeleton . It consists of bones and cartilage, completely covered with body tissues.
The external skeleton is characteristic mainly for invertebrates, but may also be present in vertebrates. It does not hide inside the body, but completely or partially covers it from above. The exoskeleton consists of various organic and inorganic compounds, for example, chitin, keratin, limestone, etc.
Not all organisms possess only one type of “framework”. Some species have both internal and external skeletons. These animals include turtles and armadillos.
Polyps
Polyps are one of the most "lazy" creatures on the planet. They preferred not to move on their own, but to live, clinging to the seabed, like plants. Only the sea anemone does not have a solid skeleton. In the rest, it is represented by protein (gorgonaria, black coral) or lime (madreporovye).
The calcareous outer skeleton is commonly called coral. In its small holes are the polyps themselves, connected to each other by a membrane of living tissues. Animals form entire colonies. Together, their exoskeletons form an “underwater forest” or reefs that host entire islands.
The main part of the reefs is located in the waters of Southeast 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.
Mollusks
Shellfish have one of the most beautiful and diverse outdoor 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. It may include aragonite or conchiolin with impurities of calcite, vaterite, calcium carbonate and calcium carbonate.
Some animals have a spiral shell, the curls of which are twisted in a circle (snails) 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.
At tsipreya or snake, each new curl overlaps the previous one, which makes the spiral poorly distinguishable, and it seems that it does not exist at all. But bivalves do not have it. Their sink consists of two convex symmetrical parts that open and close like a casket.
The skeletons of mollusks are generally not smooth. They are covered with microscopic scales, grooves and bulges. In some species, spines, keels, ridges and plates from variations of calcium carbonate extend from shells.
Arthropods
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 external skeleton of arthropods is very different from the covers of corals and mollusks.
Durable cuticles (sclerites) of chitin and other impurities, which are interconnected by elastic and flexible membranes, provide mobility to the animal, enveloping each segment of their body.
In insects, a strong but elastic cuticle represents the outer layer of the skeleton. Underneath is a layer of hypodermis and basement membranes. It consists of fat-protein complexes that prevent the body of animals from drying out.
In crustaceans, the cuticle is more durable and saturated with lime, which over time becomes more and more. In some species, the skeleton may be transparent and soft.
The cuticle contains pigments that give animals a diverse color. From above, it is usually covered with scales, outgrowths and hairs (chetoids). In some representatives, the integument is equipped with glands that secrete poison or odorous substances.
Vertebrates
Strong outer coverings are also found among more developed animals. The external skeleton of turtles is represented by a shell. It is a reliable protection for the animal, as it can withstand the severity of two hundred times the weight of its owner.
The carapace consists of a thick upper keratin layer in the form of tightly bonded shields and an internal bone layer. The spine and ribs are attached to them from the inside, repeating the arched shape of the shell. The part of the skeleton that covers the back is called carapace, and the abdominal shield is called plastron. All scutes on them grow independently of others and acquire annual rings when the animal falls into winter sleep.
The shells can have different colors and patterns, but basically their color is disguised as the external environment. Star turtles have black and convex shields, with yellow “stars” in the center. At the African Kiniks, it is more restrained and has a solid yellow-brown color.