Type of echinoderm: characteristic

The size of invertebrate creatures belonging to this type ranges from 5 cm to 50. But there are species whose dimensions can be several millimeters, or vice versa, two meters.

All the “residents” studied by scientists differ from each other in their structure. But, of course, there are a number of signs by which these vertebrates can be distinguished from others. marine life. All these signs have not undergone any changes, and have not undergone evolution over time.

Sea stars are echinoderms

Type echinoderms, main features:

1. Only these marine inhabitants have a special ambulacral (water-bearing) system. It consists of a group of channels with thin walls filled with liquid;
2. In their structure, they are radiant (usually this is an internal skeleton, well developed, the rays are a multiple of five).

Holothuria ( sea ​​cucumber) - a representative of echinoderms

With help ambulacral system representatives of the echinoderm type are able to move, touch objects. And in some varieties of sea lilies and hedgehogs, it can perform the function of breathing. This whole system consists of the same type: an annular channel, which with inside surrounds mouth opening, and radial channels, divisible by 5, extending from the annular one. They end blindly or with a sensitive process.

If we talk about the characteristics of echinoderms, then one more hallmark of these vertebrates is that their skeleton is laid in the connective layer of the skin and it is calcareous. The outer epithelium of most representatives of echinoderms is covered with an uneven layer of cilia. They are designed to cleanse the body of impurities, perform a respiratory function and feed food into the mouth opening.

Sea lily

The outer layer of the epidermis may contain a large number of specific glandular cells that secrete a poisonous or sticky enzyme. There are some species such as echinoderms that secrete enzymes that can glow.

Skeletal plates in echinoderms are arranged like rays. But this is manifested not only from the outside, but is also displayed on the internal organs of these sea creatures. For example, nervous and circulatory system also have a radiant arrangement.

Representative of echinoderms - ophiura

Zoologists believe that the senses of smell and taste are well developed. They are represented by a large number of sensitive cells located on ambulacral legs, which is an important aspect in the characteristics of echinoderms. Creatures of this class are able to perceive taste stimuli at great distances.

Also, the radiant structure has their reproductive system. It consists of a cord and gonads. Much depends on the variety of the echinoderm type, the gonads are located in grape-shaped sacs, which are placed either in the radial base or go deep into it.

The digestive organs do not have a similar structure. At different types echinoderms they are arranged differently. This may be due to the difference in nutrition. The presence of skeletal plates or its absence may also depend on nutrition. In some species of these representatives of vertebrates, the mouth may be surrounded by tentacles that help in catching prey.

Sea urchin "Slate pencil"

Despite various characteristics echinoderms, scientists have not yet fully understood the complete process of digestion in these creatures. What is clear is that the walls of their intestines contain a large number of cells that secrete digestive juices and enzymes. Also, no answer was found to the question of the excretion of the decay products of these invertebrates. Representatives of the echinoderm type do not have special organs for their excretion.

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scientific classification

1. Class Starfish
2. Ophiura class (Snaketails)
3. Class Sea cucumbers (holothurians)
4. Class Sea lilies
5. Class Sea urchins

sea ​​urchins And holothurians belong to echinoderms, like starfish. They have the characteristic abilities of echinoderms - thin tube legs, and many species also have numerous needles, which they use both for protection and for movement, as if on stilts. Some types of sea urchins are poisonous. sea ​​urchins are rounded, flattened or spherical shape body. This group got its name from the needles found in most species. Sea urchins, like and, have five-ray symmetry. But their rays grow together, forming a spherical body. Sea urchins can walk slowly on their quills, in addition, they can crawl with the help of very long flexible tubular legs. Sea urchins feed on algae and small animals like those that cover the surface of water rocks. Some species, such as the heart-shaped hedgehog, have a more elongated body shape, resembling a heart. This structure makes it easier for them to burrow into the sand. There is a species called sea potatoes. Its brown, potato-like shell or shell can be found on the beach.
Holothurian also called sea ​​cucumbers for an elongated warty body resembling a cucumber. Unlike other echinoderms, holothurians have a soft body in a dense leathery shell. The animal's mouth is surrounded by retractable tentacles. Holothurians slowly move along the seabed with the help of three rows of tubular legs. If the holothurian was disturbed or someone attacked it, it is able to throw out the insides, including the stomach and intestines, on the enemy. This sticky mass repels most predators and keeps even lobsters at bay. Holothuria easily restores lost organs.

Other echinoderms:

sea ​​urchins
- 950 species
- Spherical, sometimes with spikes
- Beams fused

Holothurians
- 1150 species
- long oblong body
- No rays
- Tentacles around the mouth

Other marine animals:

tunicates (sea squirts)
- 1400 species
- Sedentary or plankton filter feeders
- Larvae are more complex than adults

lancelets
- 25 types
- Small, up to 10 cm
- fish body
- No eyes or fins

Holothurians, or sea pods, or sea ​​cucumbers(lat. Holothuroidea) - a class of invertebrate animals such as echinoderms. Species eaten are common name"trepang".

The modern fauna is represented by 1150 species, divided into 6 orders, which differ from each other in the shape of tentacles and calcareous ring, as well as the presence of some internal organs. The oldest fossils of holothurians date back to the Silurian period.

Despite the fact that the holothurian is usually called sea ​​cucumber, this is a real animal belonging to a separate class of invertebrates such as echinoderms, like sea ​​urchins, starfish, serpentine - brittle stars and sea lilies.

The ancient Greeks called these unusual marine inhabitants echinoderms, while they were combined either with worms or with intestinal animals. Then such names of this type of animals appeared as radiant, zoophytes, i.e. semi-plants, semi-animals (like sponges), and only at the end of the 19th century they were singled out as an independent and unique type animals under modern name echinoderms.

At present, animals of the echinoderm type are considered by zoologists to be the most highly organized representatives of invertebrates.

They can be found in many seas and oceans, from shallow coastal waters to deep sea trenches (for example, deep sea species are present in the genera Paelopatides and Paroriza). The most common sea cucumbers in the waters of the tropics and subtropics, preferring to settle Coral reefs and rocky soils overgrown with dense vegetation.

Holothurians are very ancient animals. The age of some of the fossilized remains that fell into the hands of specialists was estimated at 450 or even more million years. According to scientists, these animals appeared in the Cambrian period, that is, at least 500 million years ago.

Holothurians- absolutely unique animals. Like starfish, urchins and brittle stars, they have a pronounced five-ray body symmetry, and move along the bottom on tiny tube legs, setting them in motion, pumping water through the channels of these tubes.

But there are also significant differences in the body structure and appearance of holothurians and other echinoderms. They have an elongated body, resembling either a cucumber or an oblong spheroid, and sometimes a short worm. There are no pronounced rays or long needles on the body of these animals.

Their skeletal lattice is represented by small calcareous formations in the form of blunt needles - spicules, occurring in the walls of the body. The spines of some species are sharp and hard, you can even get hurt on them.

If you touch the skin of the holothurian with your hand, it will seem wrinkled and rough to the touch. The body is elastic, muscular, since five ribbons of longitudinal muscles are radially located in it, stretching from the mouth to the anus.

Around the mouth is a corolla of short tentacles, with which the holothurian captures prey and pulls it into the mouth. The tentacles are not capable of significant contractions, since they are not equipped with the appropriate muscles for this.

esophagus sea ​​cucumbers has the appearance of a spirally wrapped intestine, surrounded by a calcareous ring, which serves as a support for the longitudinal muscles.

Holothurians reproduce by eggs. Individuals have a sexual difference (males and females), but outwardly they are difficult to distinguish. Fertilization of eggs is most often external, but there are also species in which the offspring develops in the body of the female. Holothurians live on average 5-10 years.

The body color of holothurians of different species can be brown, brown-red (of different shades), green, yellowish-green, and even black or white. There is information that there are also blue holothurians, to which popular rumor ascribes numerous medicinal healing properties bordering on the miraculous. Perhaps such albinos are found in nature, but the healing properties of their color are probably just a beautiful legend. The color of the body of holothurians largely depends on the habitat - it has been noticed that the skin color of these animals tends to harmonize with the color of the underwater landscape.

Body sizes in holothurians of different species can vary from a few centimeters to five meters (the record holder is the spotted synapta Synapta maculata), but most often individuals are from 30 cm to a meter long.

The way of life of sea cucumbers is inactive - they usually slowly crawl along the bottom, filtering edible particles of organic matter from the soil. It is curious that at the same time they are located on their side, since the ambulacral legs that serve them for movement are located on the side of the body. These primitive animals feed on small living organisms - benthos, i.e. plankton, which lives in the bottom layers of water. But the basis of the diet of holothurians is the organic remains of dead organisms, constantly sinking to the bottom from different depths of the strata. sea ​​waters. For this reason, holothurians are called orderlies of the sea, and indeed, their role in cleaning the seabed from microscopic carrion can hardly be overestimated.

These animals have another amazing ability- they can turn their stomach out through the cloaca and throw out its contents, sometimes even with internal organs. This method of holothuria is often used in moments of danger, when it is necessary to escape from the enemy. Since holothurians move more slowly than turtles on their short legs, they have to sacrifice their entrails to divert the predator's attention.
And the unique ability of holothurians to regenerate body parts and even internal organs helps them recover the loss in just two to three weeks. As they say - lizards are resting.

The natural enemies of holothurians include starfish, some types of mollusks, predatory fish and crustaceans, which are indifferent to the toxins produced by sea cucumbers.

The poisonous filling of the stomach of many holothurians makes it difficult to keep them in aquariums - they can kill not only other pets of an artificial reservoir, but also die themselves in a cloud of toxin. For this reason, it is not recommended for inexperienced amateurs to settle holothurians in their aquarium.

Among these animals there are edible species, which are called trepangs (for example, many representatives of the genera Holothuria, Bohadschia, Actinopyga, Microthele, etc.).
Trepangs are eaten by many Asian peoples (Japanese, Chinese, Malays, etc.) - they are caught by commercial methods and brought to the table in dried, smoked, boiled, fried or canned form. There are even dishes made from raw sea cucumbers.

Echinoderms are a special type of invertebrates that live on the bottom of the oceans. These amazing creatures existed on Earth long before the appearance of man on it (more than 500 million years ago). There are up to 7,000 species of echinoderms, however, paleontologists emphasize that about 2/3 (13,000) species have disappeared in evolutionary process. To date, the main representatives of echinoderms are starfish, lilies, hedgehogs, holothurians ("sea cucumbers") and brittle stars ("serpenttails"). We invite you to learn about echinoderms - Interesting Facts about appearance, internal structure, impact on the environment.

Appearance

Growths on the calcareous skeleton. It is because of this that the animals got their name. Often, growths, spikes and needles can be mobile - in this way they defend themselves.

Various sizes. Since echinoderms have a large number of species, it is obvious that they all differ from each other in size and appearance (balls, flowers, barrels). The fossil remains of prehistoric representatives confirm that a very long time ago they could reach even up to 20 meters in length.

body symmetry. This feature due to the fact that these living organisms move very little. Some species even have sedentary image life (for example, sea lilies).

Internal structure

Flexible body. The most striking feature of echinoderms is their ability to change the hardness of their bodies. Depending on the need, they can vary the stiffness of the connective tissues and integuments of their body and become elastic (up to the consistency of jelly) or, on the contrary, hard.

Nutrition. The diet is unlimited - these marine inhabitants are omnivores. However, some individuals, due to the characteristics of the organism, are not able to digest food entirely. Thanks to the aforementioned ability, such species can envelop food with their body and carry out the process of external digestion.

Simple internal system. Echinoderms are able to get along both at depths and in shallow water. And yet, a rather primitive internal water-vascular system does not allow them to tolerate changes in the salinity of the water.

Environmental impact

Threats to anglers. Representatives of the fishing industry do not particularly favor these inhabitants of the sea. The reason is simple: these creatures (more often referred to as starfish and other predators of this species) destroy a lot of mollusks suitable for human food.

Marine paramedics. In general, echinoderms are an integral part of the marine fauna. They not only destroy the remains of dead living organisms, but also act as excellent natural filters, as they feed on planktonic organisms that pollute the upper layers of the ocean.

Utilization of carbon dioxide. And also starfish and other species absorb up to 2% of carbon emitted by humans, which means 0.1 gigatonnes annually.

Of course, echinoderms deserve the title of one of the most extraordinary and beautiful marine life. Don't forget the environmental benefits!