Marine invertebrates. Echinoderm crinoids of coral reefs Disc anemones and zooanthids
Perhaps the most interesting group of echinoderms are starfish. If the vast majority of other Echinoderms are created
Although the stars are, to put it mildly, inactive, the stars are active predators, spending a significant part of their lives in motion. True, you can’t call them sprinters. A saucer-sized star crawls at an average speed of six meters per hour. But in case of emergency, it can rush for some time at a speed of up to twenty meters per hour. This speed, by the way, is quite enough to catch up with many mollusks. Most stars are predators. Many have a mouth that can stretch wide and swallow whole bivalve mollusks, sea urchins, and their own smaller brethren. Among the stars there are those who are able to turn their own stomach outward, pull it over the victim and digest it without swallowing it. The stomach of these stars is thin and stretches like rubber. A narrow gap between the shells is enough for a star to stick its stomach inside, and the mollusk comes to an end. Many stars create this gap themselves. Having clasped the shell with rays (they are quite mobile in many stars), the star sticks to the valves with ambulacral legs and pushes these valves apart, like Samson's mouth of a lion. As we have already said, it is enough for the star to slightly open the sash. The force that a star the size of a plate develops in this case can reach five kilograms. A normal mussel or oyster is not capable of withstanding such power. Even sufficiently mobile and strong animals, if the star touched them with a beam, find themselves in a peak position - sucking
A starfish clasping a clam shell and trying to open it
the ambulacral legs are held firmly, and the star manages to wrap its rays around the prey before it manages to shake off the echinoderm. There are species of large stars in which the rays are almost as mobile as the tentacles of an octopus, and they even manage to catch fish. True, only the sick or the crippled - a healthy fish is too agile for a star.
Starfish are very gluttonous and bring the owners of oyster jars to hysterics. In many places, oyster colonies have to be fenced off, otherwise delicacy mollusks do not end up in restaurants, but in the stomach of echinoderms. In general, it is very difficult to fight with the stars. It is not enough to catch them, they must also be killed, which is quite difficult. In one of the areas where oyster farming was the main source of income, they somehow tried to collect stars with a dredge, and then chop them into pieces. It ended badly, because from each severed ray a new star grew.
About fifty years ago, the starfish acanthaster caused a lot of panic in the world. This star feeds on coral polyps and destroys them in abundance. Behind the creeping star is a strip of dead coral. Suddenly, for unknown reasons, the number of acanthaster increased catastrophically in many areas and in a number of places they killed corals in areas of several kilometers each. After the death of polyps, coral reefs began to be destroyed by waves, and a threat arose to many small islands that these reefs protected from ocean run-up. An urgent and unsuccessful search for ways to combat this scourge began. But after a few years, the number of stars returned to normal as suddenly as it had grown before, and the danger was over.
Well, in conclusion, it should be said that starfish (and very similar brittle stars), sea urchins and sea cucumbers are the younger generation of the venerable type of echinoderms. From the point of view of the older generation, these are obscenely mobile, restless and cunning creatures. The fact is that the older generation, from which hedgehogs and stars originated, is generally led by a completely motionless sea lily.
lifestyle, similar to the coelenterates. More precisely - led. In our time, only a small class of sea lilies remains from the huge variety of these creatures. And once these ancient echinoderms were numerous in all the waters of the Earth and competed with the intestinal cavities in abundance and diversity.
So the history of echinoderms is unique. Their ancestors were quite normal "worms" who switched to a sedentary lifestyle. It was then that they developed such an unusual body shape and, probably, the nervous system and other organs were greatly simplified. But then some of these creatures, whose structure is superbly adapted to a sedentary existence and deprived of everything that is necessary for movement, for some completely unimaginable reasons, again switched to an active life. And if going into a "sedentary" life is a completely common thing for worms, then a return to a mobile life is an extraordinary rarity.
Echinoderms are peculiar animals. They cannot be compared in structure with other types. these animals are reminiscent of a flower, a star, a cucumber, a ball, etc.
History of study
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). 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.
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 - 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 benthic, most of which are free-living organisms. Less common are those 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 lack special ones. 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 invaginating parts of the body.
External 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 flow 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 various glands (luminous and poisonous) and pigments that give these animals an amazing color.
The skeletal elements of starfish are calcareous plates, which 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 musculature of these animals is 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: free-moving echinoderms are represented by brittle stars, holothurians, sea urchins and starfish, while attached ones are represented 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 live only in salt water.
Sea stars
The most famous representative of the type of interest to us is the starfish (a photo of one of them is presented 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.
See 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 quickly regenerate. 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, if necessary, can crush its shell.
The most famous among them is Acanthasterplanci - the crown of thorns. This is the worst enemy of marine coral reefs. There are about 1500 species in this class (type echinoderms).
Sea stars are able to reproduce both sexually and asexually (regeneration). The bulk of these animals are dioecious organisms. They fertilize in water. The organism develops with metamorphosis. Some starfish live up to 30 years.
Serpenttails (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.
sea lilies
Echinoderms are very diverse. Examples of crinoids that are also of this type are presented above. These organisms are exclusively benthic. They lead a sedentary lifestyle. It should be emphasized that crinoids 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, however, in the Mesozoic and Paleozoic eras, their role in the waters of the seas and oceans was very great.
Sea cucumbers (holothurians)
These organisms are called differently: 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 drugs are obtained from them (for example, holothurin).
Currently, about 1150 species of sea cucumbers are represented. Their representatives are divided into 6 groups. The Silurian period is the time to which the oldest fossils of holothurians belong.
These organisms differ from other echinoderms in their oblong, spherical or worm-like shape, 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 15 are extinct.
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) with its help not only get food, but also modify rocks by drilling holes in them.
The value of sea urchins
These animals are a valuable type of biological resources of the sea. Commercially interesting mainly 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 for 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.
Considering the above, it is not surprising 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, such a long life expectancy in this country, where people live on average 89 years, is associated with the use of this food product.
In this article, only the main echinoderms were presented. We hope you remember their names. Agree, these representatives of the marine fauna are very beautiful and interesting.
Echinodermata (Echinodermata) is a type of invertebrate deuterostome. Their characteristic feature - the radial symmetry of the body - is secondary and developed under the influence of a sedentary lifestyle; the earliest echinoderms were bilaterally symmetrical.
The internal structure of the starfish
The size and shape of the body of echinoderms is very diverse. Some fossil species reached a length of 20 m. Usually the body is divided into five rays, alternating with inter-ray spaces, however, there can be 4, 6, 13, and even 25 rays. skeleton with needles. The mouth of attached echinoderms is on top (not far from the anus), in freely moving echinoderms it is turned in the opposite direction.
The structure of the ambulacral system
Another characteristic feature of echinoderms is the ambulacral system, which consists of fluid-filled canals and serves for movement, respiration, touch, and excretion. Filling the relaxed canals of the ambulacral system with liquid, echinoderms stretch in the direction of movement, sticking to the ground or some object. A sharp contraction of the lumen of the channels pushes water out of them, as a result of which the animal pulls the rest of the body forward.
The intestines are in the form of a long tube or voluminous bag. The circulatory system consists of annular and radial vessels; the movement of blood is caused by the axial complex of organs. The excretion is carried out by amoebocytes, which are excreted through a gap in the body wall to the outside along with the decay products. The nervous system and sense organs are poorly developed. Some echinoderms, escaping from enemies, are able to discard individual rays and even most of the body with the entrails, regenerating them subsequently within a couple of weeks.
All echinoderms are crushed sexually; starfish, brittle stars and holothurians are capable of dividing in half, followed by regeneration of the missing half. Fertilization takes place in water. Development proceeds with metaformosis; there is a free-swimming larva (in some species, the larvae remain in the female's brood chambers). Some echinoderms live up to 30 years.
The type is divided into two subtypes; riveted echinoderms are represented by crinoids and several extinct classes, free-moving ones by starfish, sea urchins, holothurians and brittle stars. About 6000 modern species are known, twice as many extinct species. All echinoderms are marine animals that live only in salt water.
Consider briefly the main classes of echinoderms.
The crinoids (Crinoidea) are the only modern class of attached echinoderms. In the center of the cup-shaped body is the mouth; a corolla of feathery branching rays departs from it. With their help, the sea lily captures the plankton and detritus that it feeds on. A stalk up to 1 m long or numerous movable processes extend down from the calyx, with which the animal is attached to the substrate. Stemless sea lilies are able to slowly crawl and even swim. The total number of species is about 6000; less than 700 of them currently exist. Crinoids have been known since the Cambrian.
Most sea stars (Asteroidea), in full accordance with the name, have the shape of a flattened five-pointed star, sometimes a pentagon. However, among them there are species with more than five rays. Many of them are brightly colored. Starfish are predators that can slowly crawl along the bottom with the help of numerous ambulacral legs. Some species are able to invert the stomach, wrapping it around a prey, such as a mollusk, and digesting it outside the body. About 1500 species; known from the Ordovician. Some starfish are harmful by eating commercial oysters and mussels. The crown of thorns destroys coral reefs, and touching it can cause severe pain.
The body of the brittle star or serpentine (Ophiuroidea) consists of a flat disk up to 10 cm in diameter with 5 or 10 flexible segmented rays extending from it, the length of which is sometimes several tens of times greater than the size of the disk. Some ophiurs are viviparous. The brittle stars crawl by bending rays, feed on small animals or detritus. Tropical species are brightly colored, some are able to glow. Ophiurs live on the seabed at a depth of up to 8 km, some live on corals, sponges, sea urchins. About 2000 species; known from the Ordovician.
Sea urchins (Echinoidea) are another class of echinoderms. A disc-shaped or spherical body up to 30 cm in size is covered with skeletal plates bearing long and thin needles. One of the most important purposes of these needles is protection from enemies. Some sea urchins feed on detritus; others, scraping algae from stones, have a mouth with a special chewing apparatus - an Aristotelian lantern resembling a drill. With it, some sea urchins not only feed, but can also drill holes in the rocks. Sea urchins move with the help of ambulacral legs and their spines. About 800 species at depths up to 7 km. The caviar of some species is edible. A number of sea urchins are poisonous.
Holothurians or sea cucumbers (Holothurioidea) really look like cucumbers up to 2 m long. The skeleton is greatly reduced. The mouth is surrounded by a corolla of tentacles that serve to capture food. With strong irritation, they are capable of autotomy. Holothurians are bottom (very rarely - pelagic) sedentary animals that feed on silt or small plankton. About 1000 species in the seas and oceans. Trepang in the Far East is eaten.
Starfish, sea urchins, brittle stars, holothurians (sea cucumbers) belong to the type of echinoderms. Echinoderms existed already 520 million years ago. Fossil forms of echinoderms reached 20 meters in length! About 6 thousand species have survived to our time. Echinoderms live in the seas and oceans, and inhabit them to the greatest depths. Starfish were found at a depth of 7.5 kilometers!
Characteristic features of this type are ray symmetry, and the number of rays is usually a multiple of 5, as well as an amazing water-vascular (ambulacral) system, which nature has not endowed with anyone except echinoderms. Their body is pierced by channels filled with sea water. This sea water is not communicated with the outside. By distilling water inside their body, echinoderms control the movement of special legs with suction cups and tentacles, they can move and capture food. Such a “hydraulic” way of movement is not very fast (usually about 10 m / h), but, apparently, this speed is quite enough for echinoderms.
After all, for example, starfish hunt mainly for mollusks, which, as you know, are also not fast walkers. True, sometimes they grab stars and live fish. The fish can swim away, dragging a star on itself, but this will not hurt the predator - it will digest the victim on the go. And the method of digesting large prey in starfish is very original - the star turns its stomach out of its mouth and covers it with fish or puts it into the shell of the prey through the gap. So it digests, right in the sea water.
Ofiura grabs her sponge.
Sea stars.
The largest of the sea stars (from the family breezingid) has a span of tentacles over 130 cm. The heaviest starfish weigh up to 6 kg. The most dangerous pests people consider starfish that eat coral. For example, one starfish - a crown of thorns, living in the Pacific and Indian oceans, can destroy up to 400 square meters per day. see corals. And what remains of coral after the invasion of hundreds of thousands of starfish?
Further
Sea lilies are representatives of the amazing world of bottom animals. The name of this creature from the ancient Greek language is translated as "looks like a lily." Yes, this is not a flower, as many people think, although together with algae and corals they can form underwater gardens of unprecedented beauty. From this article you will find out which group the sea lily belongs to, where a lot of other interesting facts about this unusual animal live.
Evolution
Compared to other echinoderms, their way of feeding seems rather primitive. A lily with a loose corolla forms a whole network that serves to trap detritus and plankton. On the inside of the arms, there are ambulacral ciliary grooves that lead to the mouth. They are equipped with glandular cells that secrete mucus, which envelops the particles caught in the water and turns them into food lumps. Through the grooves, all the food obtained in the water enters the oral opening. The amount of food depends on the branching of the rays and their length.
- Stem lilies are one of the most ancient creatures living to this day on our planet, but these marine inhabitants were discovered relatively recently. The lily was first described in 1765, after an individual was found off the coast of the island of Martinique in the Atlantic Ocean. They called it the sea palm.
- Lily Bathycrinus complanatus was found near the Commander Islands (Pacific Ocean) at a depth of more than 2800 meters. Its length is only a few centimeters. This fragile creature is attached to the substrate with the help of short roots growing only at the base of the stem. The rest of it is generally devoid of cirrhosis.
- The stemless lilies of the Komatulidae order freely crawl or swim in the water, holding their mouth opening only upwards. If you turn it over, then it will immediately take its original position. Comatulids move at a speed of about 5 meters per minute and at the same time make about 100 swings of their rays, gracefully raising and lowering them.
- Among the lilies that live in the waters of Antarctica, there are species that take care of their offspring, for example, representatives of the Bathymetridae family - Phrixometra nutrix (viviparous frixometer). Her embryos are in brood bags, where they go through all the stages of their development. Watching the females of this species, you can find tiny pintacrinus on it. They are securely attached with their stalk to the brood bags. They leave the mother's body only as a fully formed small individual - a comatulid.