Echinoderms are peculiar animals. They cannot be compared in structure with other types. The appearance of these animals resembles a flower, a star, a cucumber, a ball, etc.
Study history
Even the ancient Greeks gave them the name "echinoderms". Representatives of this species have long been of interest to man. The history of their study is connected, in particular, with the names of Pliny and Aristotle; and in the 18th and early 19th centuries they were studied by many famous scientists (Lamarck, Linnaeus, Klein, Cuvier). Nevertheless, most zoologists at that time correlated them with either coelenterates or worms. I. I. Mechnikov, a Russian scientist, found out that they are related to the enterobranchs. Mechnikov showed that these organisms are closely related to representatives of chordates.
Echinoderm diversity
In our time, it has been established that echinoderms are animals that belong to the group of the most highly organized invertebrates - deuterostomes. They appeared on our planet more than 520 million years ago. The remains of echinoderms are found in sediments dating back to the early Cambrian. This type includes about 5 thousand species.
Echinoderms are marine, bottom-dwelling animals, most of which are free-living organisms. less oftenfound attached to the bottom with a special stalk. The organs of most organisms are located along 5 rays, but their number in some animals is different. It is known that the ancestors of echinoderms had bilateral symmetry, which free-swimming larvae of modern species have.
Internal structure
In representatives of echinoderms, a skeleton develops in the subcutaneous connective layer, consisting of calcareous plates and needles, spines, etc. on the surface of the body. As in chordates, in these organisms the secondary body cavity is formed by the separation of mesodermal sacs from the intestine. The gastropore during their development overgrows or transforms into the anus. In this case, the mouth of the larva is formed anew.
Echinoderms have a circulatory system. Nevertheless, their respiratory organs are rather poorly developed or completely absent. It is necessary to briefly describe other features of echinoderms. These animals do not have special excretory organs. The nervous system of the organisms we are interested in is rather primitive. It is located partially in the skin epithelium or in the epithelium of parts of the body that bulge inwards.
Exterior structure
The characteristics of echinoderms should be supplemented by the features of the external structure of these organisms. The outer epithelium of the main part of echinoderms (with the exception of holothurians) has cilia that create a current of water. They are responsible for the supply of food, gas exchange and cleansing the body of dirt. In the integument of echinoderms there are a variety of glands (causing luminescence and poisonous) and pigments that give amazing colorthese animals.
The skeletal elements of starfish are calcareous plates that are placed in longitudinal rows, usually with spines protruding outwards. The body of sea urchins is protected by a calcareous shell. It consists of a series of plates tightly connected to each other, with long needles sitting on them. Holothurians have calcareous bodies that are scattered over their skin. The skeleton of all these organisms is internal in origin.
Musculature and ambulacral system
The muscles of these animals are represented by muscular bands and individual muscles. It is developed quite well, as much as this or that animal is mobile. In most species of echinoderms, the ambulacral system is used for touch, movement, and in some sea urchins and sea lilies it is for breathing. These organisms are dioecious, they develop with larval metamorphosis.
Classification of echinoderms
There are 5 classes of echinoderms: brittle stars, sea stars, sea urchins, sea lilies and sea cucumbers. The type is divided into 2 subtypes: freely moving echinoderms are represented by brittle stars, holothurians, sea urchins and starfish, and attached ones by sea lilies, as well as some extinct classes. About six thousand modern species are known, as well as twice as many extinct ones. All echinoderms are marine animals that only live in s alt water.
Starfish
The most famous representative of the type of interest to us is the starfish (photo of one of thempresented above). These animals belong to the class Asteroidea. Sea stars are not accidentally given this name. In their form, many of them are a five-pointed star or a pentagon. However, there are also such species, the number of rays of which reaches fifty.
Look what an interesting body the starfish has, the photo of which is presented above! If you turn it over, you can see that on the underside of the rays there are rows of small tubular legs with a suction cup at the end. The animal, sorting through them, crawls along the seabed, and also climbs vertical surfaces.
All echinoderms have the ability to regenerate quickly. In a starfish, every ray that has separated from the body is viable. It immediately regenerates and a new organism emerges from it. Most starfish feed on the remains of organic matter. They find them in the ground. Their diet also includes fish carcasses and algae. However, some representatives of starfish are predators that attack their prey (non-motile invertebrates). After the prey is found, these animals dump their stomach out. Thus, digestion in some predatory starfish is carried out externally. The rays of these animals have very powerful muscles. It allows them to easily open the clam shells. Starfish can also crush its shell if necessary.
The most famous among predatory animals is Acanthasterplanci - the crown of thorns. This is the worst enemy of marine coral reefs. There are about 1500 species in this class (typeechinoderms).
Sea stars are able to reproduce both sexually and asexually (regeneration). Most of these animals are dioecious organisms. They fertilize in water. The organism develops with metamorphosis. Some starfish live up to 30 years.
Snaketails (brittle stars)
These animals are very reminiscent of stars: they have thin and long rays. The ophiuroids (type echinoderms) do not have liver appendages, anus and hindgut. In their way of life, they are also similar to starfish. These animals are dioecious, but are capable of both regeneration and asexual reproduction. Some species are luminous forms.
The body of the serpentine (ofiur) is represented by a flat disk, the diameter of which is up to 10 cm. 5 or 10 thin long segmented rays depart from it. Animals use these curving beams to move around, with which they crawl along the seabed. These organisms move in jerks. They stretch forward two pairs of their "arms", after which they sharply bend them back. Serpenttails feed on detritus or small animals. Ophiurs live on the bottom of the sea, sponges, corals, sea urchins. There are about 2 thousand of them. These animals have been known since the Ordovician.
Crino lilies
Echinoderms are very diverse. Examples of crinoids, which are also of this type, are presented above. These organisms are exclusively benthic. They lead a sedentary lifestyle. It should be emphasized that marinelilies are not plants, but animals, despite their name. The body of these organisms consists of a calyx, stem, and arms (brachioles). They use their hands to filter food particles from the water. Most modern species are free-floating and stemless.
Stemless lilies can crawl slowly. They can even swim in water. Their diet consists of small animals, plankton, algae residues. The total number of species is estimated at 6 thousand, of which less than 700 are currently represented. These animals have been known since the Cambrian.
Beautifully colored species of crinoids live mainly in the seas and oceans of the subtropics. They are attached to various underwater objects. It is believed that these are endangered animals, however, in the Mesozoic and Paleozoic eras, their role in the waters of the seas and oceans was very high.
Sea cucumbers (holothurians)
These organisms are called differently: sea cucumbers, sea pods or holothurians. They represent a class of invertebrates such as echinoderms. There are species that humans eat. The common name for edible holothurians is "trepang". Trepang is mined on a large scale in the Far East. There are also poisonous holothurians. Various medicines are obtained from them (for example, holothurin).
Currently there are about 1150 types of sea cucumbers. Their representatives are divided into 6 groups. The Silurian period is the time to which the oldest fossils of holothurians date.
These organisms are different fromthe rest of the echinoderms are oblong, spherical or worm-shaped, as well as the reduction of the skin skeleton and the fact that they do not have protruding spines. The mouth of these animals is surrounded by a corolla, consisting of tentacles. With the help of them, holothurians capture food. These animals are benthic, although very rare and living in the silt (pelagic). They lead a sedentary lifestyle. Holothurians feed on small plankton or silt.
Sea urchins
These animals live at the bottom or in the bottom. The body of most of them is almost spherical, sometimes ovoid. Its diameter is from 2-3 to 30 cm. Outside, the body is covered with rows of spines, calcareous plates or needles. As a rule, the plates are interconnected motionlessly, forming a shell (dense shell). This shell does not allow the animal to change shape. Today, there are about 940 species of sea urchins. The largest number of species was represented in the Paleozoic. Currently, there are 6 classes, while extinct - 15.
As for nutrition, some sea urchins use dead tissue (detritus) for food, while others scrape algae from stones. In the latter case, the animal's mouth is equipped with a special chewing apparatus called the Aristotelian lantern. In appearance, it resembles a drill. Some species of echinoderms (sea urchins) use it not only to get food, but also modify rocks by drilling holes in them.
Value of sea urchins
These animals are a valuable species of biological resourcesseas. Commercially interesting mainly caviar of sea urchins. In Japan and other countries of the Asia-Pacific region, it is a delicacy product. The caviar of these animals contains many biologically active substances. Scientists believe that the elements that are present in it can be used in cancer as a therapeutic and prophylactic agent. In addition, they normalize blood pressure, increase potency, remove radionuclides from the human body. It has been proven that eating caviar increases resistance to various infections, helps with gastrointestinal diseases, reduces the effects of radiation therapy, improves the functions of the genital and thyroid glands, and the cardiovascular system.
With all that said, it's no surprise that the sea urchin is a marine echinoderm that is becoming a coveted dish. For example, the inhabitants of Japan every year eat about 500 tons of caviar of this animal, both in its natural form and as additives to dishes. By the way, eating this food product is associated with such a long life expectancy in this country, where people live an average of 89 years.
Only the main echinoderms were presented in this article. We hope you remember their names. Agree, these representatives of marine fauna are very beautiful and interesting.
