Echinoderms: description, names, photo

Echinoderms - the animals are peculiar. They can not 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 interested in 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 either with coelenterates, or with worms. II Mechnikov, a Russian scientist, found out that they are related to the gut. Mechnikov showed that these organisms are closely related to representatives of chordates.

Variety of echinoderms

In our time, it has been established that echinoderms are animals that belong to the group of the most highly organized invertebrates - to the second-born invertebrates. They appeared on our planet more than 520 million years ago. Remains of echinoderms are found in sediments belonging to the early Cambrian. This type includes about 5 thousand species.

Echinoderms are marine animals, the bottom, most of which are free-living organisms. Less common are those attached to the bottom with a special stem. The organs of most organisms are located in 5 rays, but their number in some animals is different. It is known that the ancestors of echinoderms had bilateral symmetry, of which free-floating larvae are of modern species.

Internal structure

Representatives of echinoderms in the subcutaneous connective layer develop a skeleton consisting of calcareous plates and needles, thorns, etc., on the surface of the body. As in chordates, in these organisms the secondary body cavity is formed by the separation of the mesodermal sacs from the intestine. Gastropor during their development is overgrown or converted into anus. In this case, the larva's mouth is re-formed.

Echinoderms have a circulatory system. Nevertheless, the respiratory system is rather weak or absent at all. It is necessary to briefly describe other signs of echinoderms. These animals have no special organs of excretion. The nervous system of organisms of interest to us is quite primitive. It is located partly in the cutaneous epithelium or in the epithelium of the parts of the body that are inwardly entrapped.

External structure

Characteristics of echinoderms should be supplemented by features of the external structure of these organisms. The outer epithelium of the main part of the echinoderms (with the exception of holothurians) has cilia, which create a current of water. They are responsible for feeding food, gas exchange and cleansing the body of dirt. In the integument of echinoderms, there are various glands (causing luminescence and poisonous) and pigments, which give an amazing color to these animals.

Skeletal elements in sea stars are calcareous plates, which are arranged in longitudinal rows, usually with spines protruding outward. 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 of internal origin.

Musculature and ambulacral system

The musculature of these animals is represented by muscular bands and individual muscles. It is developed quite well, just as much as an animal is movable. In most species of echinoderms, the ambulacral system serves for touch and movement, and for some sea urchins and sea lilies it is intended for breathing. These organisms are dioecious, they develop with metamorphosis of the larva.

Classification of echinoderms

There are 5 classes of echinoderms: Ophiura, Starfish, Sea urchins, Sea Lilies and Holothuria. The type is divided into 2 subtypes: freely moving echinoderms are represented by ophiuroids, holothurians, sea urchins and sea stars, and attached - by sea lilies, as well as some extinct classes. About six thousand modern species are known, as well as about twice as many extinct species. All echinoderms are marine animals that live only in salt water.

Sea stars

The most famous representative of the type of interest is the starfish (photo of one of them is presented above). These animals belong to the class of Asteroidea. It is not by chance that starfish received such a name. In their form many of them represent 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 has a starfish, the photo of which is presented above! If you turn it over, you can see that the bottom of the rays are rows of small tubular legs that have a sucker at the end. The animal, touching them, creeps along the seabed, and also climbs on vertical surfaces.

All echinoderms have the ability to quickly regenerate. At the starfish, each ray that is 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 dead bodies and algae. However, some representatives of sea stars are predators who attack their victims (immobile invertebrates). After the extraction is found, these animals throw their stomach out. Thus, digestion in some predatory sea stars is carried out from the outside. The beams of these animals have a very powerful musculature. It allows them to easily open the shellfish flaps. Sea stars, if necessary, can also shatter its shell.

The most famous among predatory animals is the Acanthasterplanci - the crown of thorns. This is the worst enemy of marine coral reefs. About 1500 species are found in this class (type of echinoderms).

Starfish can reproduce both sexually and asexually (regenerated). The main part of these animals is dioecious organisms. Fertilization is carried out in water. The body develops with metamorphosis. Some starfish live up to 30 years.

Snake-tailed turtles (ophiuros)

These animals are very similar to stars: they have thin and long rays. In ophiuroids (type of echinoderms), there are no hepatic appendages, anal opening and posterior intestine. In their way of life, they also look like starfish. These animals are dioecious, but are capable of both regeneration and asexual reproduction. Some species are luminous forms.

The body of the snake is represented by a flat disc, whose diameter is up to 10 cm. 5 or 10 thin long articulated rays leave it. Animals use to move these curving rays, with the help of which they crawl along the seabed. These organisms are jerking. They pull forward two pairs of their "hands", then sharply bend them back. Snakebirds feed on detritus or small animals. Ophiuras live on the sea floor, sponges, corals, sea urchins. They number about 2 thousand species. These animals are known from the Ordovician.

Sea lilies

Very different echinoderms. Examples of sea lilies, which are also of this type, are presented above. These organisms are exclusively benthic. They lead a sedentary lifestyle. It should be emphasized that sea lilies are not plants, but animals, despite their name. The body of these organisms consists of a cup, stem and hands (brachioles). With the help of hands, they filter out food particles from the water. Most of the modern species are free floating and unstable.

Bezstebelchatye lilies can slowly creep. They can even swim in the water. Their diet consists of small animals, plankton, remains of algae. The total number of species is estimated at 6,000, of which at present less than 700. These animals are known from the Cambrian.

Beautifully painted species of marine lilies live mainly in the seas and oceans of the subtropics. They attach to various underwater objects. It is believed that these are endangered animals, but in the Mesozoic and Paleozoic eras, their role in the waters of the seas and oceans was very great.

Sea cucumber (holothurian)

These organisms are called in different ways: sea cucumbers, sea capsules or holothurians. They represent a class of invertebrates such as echinoderms. There are species that people eat. The general name for edible holothurians is "trepang". Trepang is mined on a large scale in the Far East. There are also poisonous holothurians. They receive various medicines (for example, holothurin).

Currently, about 1150 species of sea cucumbers are represented. Representatives of them are divided into 6 detachments. The Silurian period is the time to which the oldest fossils of holothurians belong.

These organisms differ from other echinoderms oblong, globular or vermiform, as well as the reduction of the skeleton and the fact that they do not have protruding spines. The mouth of these animals is surrounded by a whisk of tentacles. With the help of them, holothurians grab food. These animals are benthic, although very rare are those living in mud (pelagic). They lead a sedentary lifestyle. Holothurians eat small plankton or silt.

Sea urchins

These animals live on the bottom or in the bottom. The body of most of them is almost spherical, sometimes egg-shaped. Its diameter is from 2-3 to 30 cm. Outside, the body is covered with rows of thorns, calcareous plates or needles. As a rule, the plates are interconnected motionless, forming a shell (a dense shell). This shell does not allow the animal to change its shape. Today there are about 940 species of sea urchins. The greatest number of species was represented in the Paleozoic. Currently there are 6 classes, while extinct - 15.

As for nutrition, some sea urchins use dead tissues for food (detritus), while others scrape off seaweed from stones. In the latter case, the animal's mouth is equipped with a special chewing apparatus, which is called an Aristotelian lantern. It looks like a drill in appearance. Some species of echinoderms (sea urchins) with its help not only extract food, but also modify rocks, drilling holes in them.

Value of sea urchins

These animals are a valuable species of sea bioresources. In commercial terms, it is interesting mainly caviar of sea urchins. In Japan and other countries of the Asia-Pacific region, it is a delicious product. Caviar of these animals contains a lot of biologically active substances. Scientists believe that the elements that are available in it, can be used in cancer diseases as a therapeutic and prophylactic. In addition, they normalize blood pressure, increase potency, remove radionuclides from the human body. It is proved that eating caviar increases resistance to various infections, helps with gastrointestinal diseases, reduces the consequences of radiation therapy, improves the functions of the genital and thyroid glands, and the cardiovascular system.

Considering the foregoing, it is not surprising that the sea urchin is a sea echinoderm, which becomes a desired dish. For example, the inhabitants of Japan each year eat about 500 tons of caviar of this animal both in kind and as additives to dishes. By the way, with the use of this food product, such a long life span is associated in this country, where people live on average 89 years.

In this article, only the main echinoderms were represented. I hope you remember their names. Agree, these representatives of the marine fauna are very beautiful and interesting.