Invertebrate starfish. What type of invertebrate is the starfish? There are three types of starfish larvae
One of the most beautiful animals not found on land is starfish. Divers diving in warm seas often manage to admire these unusual and interesting creatures.
Echinodermata (Echinodermata), which include starfish, are an independent and very peculiar type of animal world. According to the structure of the body, they are completely different from other animals and, due to the peculiarities of organization and the original shape of the body, have long attracted attention.
Echinoderms appeared on Earth a very long time ago, more than 500 million years ago. The presence of a calcareous skeleton contributed to the good preservation of the fossil remains of the ancestors of these creatures.
In the glorious and numerous community of echinoderms, the class of starfish (Asteroidea) is represented by a huge variety of species, differing from each other in size, body shape and some differences in organization.
In the fossil state, they have been known since the Lower Paleozoic - from the Ordovician period, i.e. about 400 million years ago. There are over 1500 known modern species sea stars, which are systematized in about 300 genera and 30 families.
Opinions often differ between scientists about the number of starfish orders. Previously, they were combined into three orders - clearly lamellar, needle-shaped and pedicellarian stars. Currently, they are already divided into 5-9 different units in various sources. I think that for us it is not very important.
Sea stars- exclusively marine animals, they are not found in fresh water bodies. They do not live in heavily desalinated seas, for example, in the Azov or Caspian, although sometimes they can be represented by single oppressed species. So, for example, individuals of A. rubens stars are sometimes found in the western part Baltic Sea(near the island of Rügen), but here they do not breed, and the population of these starfish is supported by the larvae carried by the currents. And the only starfish that came from mediterranean sea in Chernoye - Marthasterias glacialis, lives only in its most saline part - in the area of the Bosphorus.
In the seas and oceans with normal salinity, starfish are found everywhere - from the Arctic to the Antarctic, and are especially numerous in the warm waters of the seas. The deep range of habitation of sea stars is also wide - from the surface layers of the sea to kilometer depths, although, of course, at great depths species diversity and the number of starfish is more meager.
About 150 species of starfish live in the Russian seas, which live, with very rare exceptions, in the northern and Far Eastern seas.
All starfish in adulthood lead a bottom lifestyle, crawling along the bottom surface or burrowing into the ground. Many of the starfish, especially those living in coastal shallow waters, are active predators that feed on various small benthic organisms - mollusks, crustaceans, other invertebrates, including echinoderms, and even fish. Do not disdain carrion.
Among deep-sea starfish, hoary-eaters predominate - they use sea soil for food, extracting organic matter from it. Some starfish can feed on plankton.
Usually, starfish are not very picky about food and will gobble up everything they can. The diet of, for example, the Chilean starfish Meyenaster includes up to 40 species of echinoderms and molluscs.
Most starfish detect and locate their prey through substances that the prey releases into the water. Some soft-bottom starfish, including species of the genera Luidia and Astropecten, are able to find burrowed prey and then excavate the substrate to reach their prey. Stylasterias forreri and Astrometis sertulifera from the west coast of the United States of America, as well as Leptasterias tenera from the east coast, grab small fish, amphipods and crabs with pedicellaria when the prey stops over or near a starfish.
Interesting way to use starfish many species of bivalve molluscs as food. The star crawls onto the body of such a prey and attaches to it with its legs on the rays, giving some effort towards opening the valves of the mollusk shell. Gradually, the muscles of the mollusc that hold the shell valves in the closed state get tired and slightly open the shell. The starfish turns its stomach inside out and squeezes it into the gap between the valves, starting the meal right inside the clam shell. Food is digested in this way in a few hours.
The inside-out stomach is a unique feeding organ for many starfish. The starfish Patiria miniata from the west coast of America, for example, spreads its stomach along the bottom, digesting organic matter that comes across.
Sea stars usually have a more or less flattened body with a central disk gradually turning into rays radiating from it. The mouth opening is located on the underside (oral) side of the disk of the starfish. Most stars have an anus on the upper body, in some species it is absent altogether. In the middle of the lower side of each beam there is a furrow, in which there are many soft and mobile outgrowths - ambulacral legs, with the help of which the starfish moves along the bottom. Typical for starfish is a five-ray structure, but there are stars with 6 or more rays. For example, the solar starfish Heliaster has 50 rays.
Sometimes the number of rays varies even among individuals of the same species. So, in the starfish Crossaster papposus, which is common in our northern and Far Eastern seas, the number of rays ranges from 8 to 16.
The ratio of the length of the rays and the diameter of the disk also varies. In some deep-sea starfish, the length of the rays is 20-30 times the diameter of the disk, while at the same time, in the common Patiria star (Patiria pectinifera) in the Sea of Japan, the rays only slightly protrude beyond the disk, which is why the star has the shape of a regular pentagon . These stars are also called biscuit stars for their similarity to flat cookies.
Even sea stars are known, whose appearance is so changed that it is difficult to recognize them as a star. A common inhabitant of coral reefs, the New Guinean cultite (Culcita novaeguineae), has a strongly swollen body, resembling a strongly swollen pillow or roll in shape. However, this body shape is only in adult stars - young culcites have the shape of regular pentagons.
Typically, sea stars that live at shallow depths have a very diverse coloration of the upper body. There may be a variety of colors and shades of the spectrum. Sometimes the coloring is spotty and form a bizarre pattern. The ventral side of the body of starfish has a more modest color, usually it is pale yellow.
The color of stars living at great depths is also paler - usually dirty gray or with shades gray flowers. Some (eg Brisinga) have the ability to glow.
The variety of color of starfish depends on the pigment inclusions located in the cells of the skin epithelium.
Dimensions various kinds starfish can vary from a few centimeters to 1 meter. Most often, divers meet starfish 10-15 cm in size.
The lifespan of some starfish species can be over 30 years.
The sense organs of the starfish are poorly developed and are represented by red eye spots located at the tips of the rays and tactile receptors located on the skin.
When you first look at a starfish, you first of all notice the numerous elements of the calcareous skeleton located on the surface of the body - plates, needles, spikes, tubercles, etc. But in fact, the skeleton of starfish is not external, like in mollusks or arthropods, but is located under the skin epithelium, sometimes very thin. The calcareous plates of starfish do not form a single integral skeleton, but are attached to each other with the help of connective tissue and muscles. Starfish have a main skeleton called a support skeleton and various appendages to it - spikes, tubercles and outgrowths that have a protective function. Sometimes such spines and bristles form a continuous cover on the upper side of the body of starfish.
Reproduction of starfish can take place in several scenarios. If a starfish with a part of the disk is torn off, then two individuals are formed from the resulting pieces of the star. The time for such regeneration can be up to 1 year. Some starfish reproduce in a similar regenerative way. In their body, softening of the connective tissue occurs and they break up into several parts, more often into two. Soon independent starfish will grow from these parts. Species of the genus of sea stars Linkia (Linckia), common in the Pacific Ocean and other regions of the World Ocean, are unique in their ability to cast rays as a whole. From each such ray, if it is not eaten by a predator, a new starfish can be regenerated. Such reproduction is called asexual.
Sea stars also reproduce sexually. Most types of stars are dioecious, i.e. represented by males and females. Reproduction is carried out by fertilization of the female eggs with the reproductive products of males, which are hatched directly into sea water. A female starfish can release several million eggs at a time.
Among the stars there are also unisexual (hermaphroidal) species. These species include, for example, the common European starfish Asterina gibbosa, which is a hermaphrodite. In such stars, both female and male reproductive products are produced in the body. Juveniles they usually bear in a special hatching bag or cavities on the back.
The larvae that hatch from the eggs usually feed on plankton and, growing up, sink to the bottom, moving on to the usual way of life for starfish.
Starfish have no natural enemies. These animals contain poisonous substances in their bodies - asteriosaponins, so predators do not honor them with attention. In addition, there are few nutrients in the body of the starfish and they do not represent a high-calorie food.
On the coral reefs of the Pacific and Indian Oceans often there is a large starfish crown of thorns or acanthaster (Acanthaster plansi), reaching a diameter of 50 cm and belonging to the genus Acanthasteridae.
It is generally accepted that starfish are completely harmless to humans, but careless handling of the crown of thorns can lead to serious trouble. The starfish crown of thorns is notorious among the inhabitants of many tropical islands. It is impossible to pick it up without getting the burning pain of the pricks of the numerous needles that cover the body of the starfish.
The crown of thorns causes a lot of trouble for pearl divers - if a swimmer accidentally steps on the body of an acanthaster, then its needles pierce the foot and break off in the human body, infecting the blood with poisonous secretions.
Local residents believe that the victim should immediately turn the crown of thorns upside down with a stick and put his foot to his mouth. It is believed that the star sucks out the fragments of its needles from the human body, after which the wounds heal quickly.
The crown of thorns, or acanthaster, is known for another unpleasant property. He is extremely fond of eating coral polyps, thereby destroying the reef itself and leaving its inhabitants without food and shelter. AT different years there have been outbreaks of significant increases in the abundance of these starfish in some regions. Then the very existence of the reefs and their inhabitants was threatened.
Significant human resources were thrown into the fight against crowns of thorns. The stars were collected in baskets and destroyed, but this did not give a tangible effect. Fortunately, crown-of-thorns outbreaks soon stopped and the coral reefs did not die completely.
Some starfish cause damage by destroying fishing grounds and plantations of oysters and mussels. Such pests are collected with special gear from the fishing areas and destroyed.
It should also be noted the useful role that starfish play in the ecology of the oceans, and the planet as a whole. These creatures intensively absorb and utilize carbon dioxide, which is becoming more and more in the Earth's atmosphere every year. Every year, starfish utilize up to 2% of atmospheric carbon dioxide. This is a very big number.
In addition, starfish are the orderlies of the seabed, eating carrion and the remains of dead marine organisms, as well as weaker and sicker individuals of marine animals.
One of the most beautiful animals not found on land is starfish. Divers diving in warm seas often manage to admire these unusual and interesting creatures.
Echinodermata (Echinodermata), which include starfish, are an independent and very peculiar type of animal world. According to the structure of the body, they are completely different from other animals and, due to the peculiarities of organization and the original shape of the body, have long attracted attention.
Echinoderms appeared on Earth a very long time ago, more than 500 million years ago. The presence of a calcareous skeleton contributed to the good preservation of the fossil remains of the ancestors of these creatures.
In the glorious and numerous community of echinoderms, the class of starfish (Asteroidea) is represented by a huge variety of species, differing from each other in size, body shape and some differences in organization.
And at the end of the post you can watch an interesting video in my opinion how the stars hang out and how they eat.
In the fossil state, they have been known since the Lower Paleozoic - from the Ordovician period, i.e. about 400 million years ago. Currently, more than 1500 modern species of starfish are known, which are systematized into approximately 300 genera and 30 families. Opinions often differ between scientists about the number of starfish orders. Previously, they were combined into three orders - clearly lamellar, needle and pedicellarian stars. Currently, they are already divided into 5-9 different units in various sources. I think that for us it is not very important.
Sea stars are exclusively marine animals, they are not found in fresh water. They do not live in heavily desalinated seas, for example, in the Azov or Caspian, although sometimes they can be represented by single oppressed species. So, for example, individuals of A. rubens stars are sometimes found in the western part of the Baltic Sea (near the island of Rügen), but here they do not breed, and the population of these starfish is supported by larvae introduced by currents. And the only starfish that penetrated from the Mediterranean into the Black Sea - Marthasterias glacialis - lives only in its most salty part - in the area of the Bosphorus.
In the seas and oceans with normal salinity, starfish are found everywhere - from the Arctic to the Antarctic, and are especially numerous in the warm waters of the seas. The deep range of habitat of sea stars is also wide - from the surface layers of the sea to kilometer depths, although, of course, at greater depths, the species diversity and number of starfish is more scarce.
About 150 species of starfish live in the Russian seas, which live, with very rare exceptions, in the northern and Far Eastern seas.
All starfish in adulthood lead a bottom lifestyle, crawling along the bottom surface or burrowing into the ground. Many of the starfish, especially those living in shallow coastal waters, are active predators that feed on various small benthic organisms - mollusks, crustaceans, other invertebrates, including echinoderms, and even fish. Do not disdain carrion.
Among the deep-sea starfish, hoary-eaters predominate - they use sea soil for food, extracting organic matter from it. Some starfish can feed on plankton.
Usually, starfish are not very picky about food and will gobble up everything they can. The diet of, for example, the Chilean starfish Meyenaster includes up to 40 species of echinoderms and molluscs.
Most starfish detect and locate their prey through substances that the prey releases into the water. Some soft-bottom starfish, including species of the genera Luidia and Astropecten, are able to find burrowed prey and then excavate the substrate to reach their prey. Stylasterias forreri and Astrometis sertulifera from the west coast of the United States of America, as well as Leptasterias tenera from the east coast, grab small fish, amphipods and crabs with pedicellaria when the prey stops over or near a starfish.
An interesting way is the use of many species of starfish in food bivalve mollusks. The star crawls onto the body of such a prey and attaches to it with its legs on the rays, giving some effort towards opening the valves of the mollusk shell. Gradually, the muscles of the mollusc that hold the shell valves in the closed state get tired and slightly open the shell. The starfish turns its stomach inside out and squeezes it into the gap between the valves, starting the meal right inside the clam shell. Food is digested in this way in a few hours.
The inside-out stomach is a unique feeding organ for many starfish. The starfish Patiria miniata from the west coast of America, for example, spreads its stomach along the bottom, digesting organic matter that comes across.
Sea stars usually have a more or less flattened body with a central disk gradually turning into rays radiating from it. The mouth opening is located on the underside (oral) side of the disk of the starfish. Most stars have an anus on the upper body, in some species it is absent altogether. In the middle of the lower side of each beam there is a groove, in which there are many soft and mobile outgrowths - ambulacral legs, with the help of which the starfish moves along the bottom. Typical for starfish is a five-ray structure, but there are stars with 6 or more rays. For example, the solar starfish Heliaster has 50 rays.
Sometimes the number of rays varies even among individuals of the same species. So, in the starfish Crossaster papposus, which is common in our northern and Far Eastern seas, the number of rays ranges from 8 to 16.
The ratio of the length of the rays and the diameter of the disk also varies. In some deep-sea starfish, the length of the rays is 20-30 times the diameter of the disk, while at the same time, in the common Patiria star (Patiria pectinifera) in the Sea of Japan, the rays only slightly protrude beyond the disk, which is why the star has the shape of a regular pentagon . These stars are also called biscuit stars for their similarity to flat cookies.
Even sea stars are known, whose appearance is so changed that it is difficult to recognize them as a star. A common inhabitant of coral reefs, the New Guinean cultite (Culcita novaeguineae), has a strongly swollen body, resembling a strongly swollen pillow or roll in shape. However, this body shape is only in adult stars - young culcites have the shape of regular pentagons.
Typically, sea stars that live at shallow depths have a very diverse coloration of the upper body. There may be a variety of colors and shades of the spectrum. Sometimes the coloring is spotty and form a bizarre pattern. The ventral side of the body of starfish has a more modest color, usually it is pale yellow.
The color of stars living at great depths is also paler - usually dirty gray or with shades of gray. Some (eg Brisinga) have the ability to glow.
The variety of color of starfish depends on the pigment inclusions located in the cells of the skin epithelium.
The sizes of different types of starfish can vary from a few centimeters to 1 meter. Most often, divers meet starfish 10-15 cm in size.
The lifespan of some starfish species can be over 30 years.
The sense organs of the starfish are poorly developed and are represented by red eye spots located at the tips of the rays and tactile receptors located on the skin.
When you first look at a starfish, you first of all notice the numerous elements of the calcareous skeleton located on the surface of the body - plates, needles, spines, tubercles, etc. But in fact, the skeleton of starfish is not external, like in mollusks or arthropods, but is located under the skin epithelium, sometimes very thin. The calcareous plates of starfish do not form a single integral skeleton, but are attached to each other with the help of connective tissue and muscles. Starfish have a basic skeleton called a supporting skeleton and various appendages to it - spikes, tubercles and outgrowths that have a protective function. Sometimes such spines and bristles form a continuous cover on the upper side of the body of starfish.
Reproduction of starfish can take place in several scenarios. If a starfish with a part of the disk is torn off, then two individuals are formed from the resulting pieces of the star. The time for such regeneration can be up to 1 year. Some starfish reproduce in a similar regenerative way. In their body, softening of the connective tissue occurs and they break up into several parts, more often into two. Soon independent starfish will grow from these parts. Species of the genus of sea stars Linkia (Linckia), common in the Pacific Ocean and other regions of the World Ocean, are unique in their ability to cast rays as a whole. From each such ray, if it is not eaten by a predator, a new starfish can be regenerated. Such reproduction is called asexual.
Sea stars also reproduce sexually. Most types of stars are dioecious, i.e. represented by males and females. Reproduction is carried out by fertilization of the female eggs with the reproductive products of the males, which are hatched directly into the sea water. A female starfish can release several million eggs at a time.
Among the stars there are also unisexual (hermaphroidal) species. These species include, for example, the common European starfish Asterina gibbosa, which is a hermaphrodite. In such stars, both female and male reproductive products are produced in the body. Juveniles they usually bear in a special hatching bag or cavities on the back.
The larvae that hatch from the eggs usually feed on plankton and, growing up, sink to the bottom, moving on to the usual way of life for sea stars.
Starfish have no natural enemies. These animals contain poisonous substances in the body - asteriosaponins, so predators do not honor them with attention. In addition, there are few nutrients in the body of the starfish and they do not represent a high-calorie food.
crown of thorns
On the coral reefs of the Pacific and Indian Oceans, a large starfish crown of thorns or acanthaster (Acanthaster plansi) is often found, reaching a diameter of 50 cm and belonging to the genus Acanthasteridae.
It is generally accepted that starfish are completely harmless to humans, but careless handling of the crown of thorns can lead to serious trouble. The starfish crown of thorns is notorious among the inhabitants of many tropical islands. It is impossible to pick it up without getting the burning pain of the pricks of the numerous needles that cover the body of the starfish.
The crown of thorns gives a lot of trouble to pearl divers - if a swimmer accidentally steps on the body of an acanthaster, then its needles pierce the foot and break off in the human body, infecting the blood with poisonous secretions
Local residents believe that the victim should immediately turn the crown of thorns upside down with a stick and put his foot to his mouth. It is believed that the star sucks out the fragments of its needles from the human body, after which the wounds heal quickly.
The crown of thorns, or acanthaster, is known for another unpleasant property. He is extremely fond of eating coral polyps, thereby destroying the reef itself and leaving its inhabitants without food and shelter. Over the years, there have been outbreaks of a significant increase in the number of these starfish in some regions. Then the very existence of the reefs and their inhabitants was threatened.
Significant human resources were thrown into the fight against crowns of thorns. The stars were collected in baskets and destroyed, but this did not give a tangible effect. Fortunately, crown-of-thorns outbreaks soon stopped and the coral reefs did not die completely.
Some starfish cause damage by destroying fishing grounds and plantations of oysters and mussels. Such pests are collected with special gear from the fishing areas and destroyed.
It should also be noted the useful role that starfish play in the ecology of the oceans, and the planet as a whole. These creatures intensively absorb and utilize carbon dioxide, which is becoming more and more in the Earth's atmosphere every year. Every year, starfish utilize up to 2% of atmospheric carbon dioxide. This is a very big number.
In addition, starfish are the orderlies of the seabed, eating carrion and the remains of dead marine organisms, as well as weaker and sicker individuals of marine animals.
Interesting Facts:
The largest of the 1600 varieties of starfish in terms of the total span of tentacles is considered to be very fragile midgardia xandaros. In the summer of 1968, a representative of this species was caught in the southern part of the Gulf of Mexico by the research vessel "Adaminos" of the University of Texas. Its length, together with tentacles, was 1380 mm, but the diameter of its body without tentacles reached only 26 mm. When dried, it weighed 70 g.
It's believed that Weight Limit of all starfish has a five-pointed Thromidia catalai living in the western part Pacific Ocean. A representative of this species, caught on September 14, 1969 in the Ailot Amedi region in New Caledonia and later exhibited in the Noumea aquarium, weighed 6 kg, and its tentacle span reached 630 mm
The smallest known was the starfish asterenids ( Patmella parvivipara), discovered by Wolf Seidler on the west coast of the Eyre Peninsula, South Australia, in 1975. It had a maximum radius of 4.7 mm and a diameter of less than 9 mm.
The crown of thorns is considered the most predatory starfish in the world ( Acanthaster planci), living in the basins of the Pacific and Indian oceans, as well as in the Red Sea. It has the ability to destroy up to 300-400 square centimeters of coral per day.
The maximum depth at which a sea avead can be found is considered to be 7584 m. At this depth, the Soviet research vessel Vityaz approximately in 1962 Mariana Trench(western Pacific) a specimen was found Porcellanaster Ivanovi.
The starfish has small patches at the tip of each ray of the star that act as light sensors and contain a red pigment that changes color. It is assumed that these areas (front sights) affect the movement of the starfish.
The starfish can feed without swallowing food. For example, when she meets a bivalve mollusk, she wraps her arms around it and turns the lower stomach inside out. It penetrates the shell, envelops the soft parts of the mollusk and digests it, and then the starfish simply draws in the diluted solution. Spiders act in a similar way - however, they do not know how to twist the stomach, but simply inject digestive juice into the victim.
Sea stars- These are very unusual animals that live in the seas and oceans. They are invertebrates, belong to the type of echinoderms and are very similar to stars, as they have rays diverging in different sides. Most often, a starfish has five rays, but there are species with three, four and six rays. The coloration of the body is often very bright and varied, on the surface there are special hard plates with needles or spikes. The sizes of stars vary greatly and can range from 2 cm to 100 cm, but most stars have a diameter of about 20 cm.
Spreading
Sea stars are widely distributed throughout the globe. They can be found in all oceans and seas and in all climatic zones, but in warm waters there are more starfish than in cold ones, and in fresh water they are not found at all.
These animals prefer a bottom way of life, more often they live in shallow water, but they can also live at a depth, but not deeper than 8.5 km.
Now on earth there are 1.6 thousand species of starfish.
Food
Almost all starfish are predators. They mainly feed on marine invertebrates - worms, molluscs, sponges, sea ducks, corals and others. Some deep sea starfish feed on the silt they find on the bottom.
The digestive system of sea stars is quite peculiar. The mouth opening is located on their ventral side, and two stomachs depart from it. One stomach has the ability to turn outward and envelop the victim, and the second stomach has ten processes that are located inside the rays of the starfish. Such an unusual digestive system allows the star to eat prey larger than itself.
Lifestyle
Sea stars are slow, sedentary animals. They usually crawl lazily along the bottom, lie still, or may climb rocks and corals in search of prey. The speed of their movement is very small - 10-30 cm per minute. The stars are considered animals, leading sedentary life. As a rule, they move away from their usual place of residence no further than 0.5 km.
In their development, stars go through several stages of development. From the eggs that adults throw into the water, larvae first form and then they gradually turn into an adult starfish. Some species of sea stars carry their larvae in special brood bags on their bodies.
Sea stars can live 20 years or more.
- Sea stars don't have a brain.
- Instead of eyes, starfish have light-sensitive cells located at the tips of their rays.
- Sea stars are capable of regeneration - from a detached beam, a new star can develop.
Brief information about the starfish.
Traditionally, on Saturdays, we publish answers to the quiz for you in the Q&A format. Our questions range from simple to complex. The quiz is very interesting and quite popular, but we just help you test your knowledge and make sure that you have chosen the correct answer out of the four proposed. And we have another question in the quiz - What type of invertebrate is the starfish?
- arthropods
- sponges
- brachiopods
- echinoderms
The correct answer is D. Echinoderm
Starfish (Asteroidea)- inhabitants sea depths, class of invertebrates such as echinoderms. In a starfish, despite its inactivity and lack of a head as such, the nervous and digestive system. And why, in fact, "echinoderms". It's all about the hard skin of the starfish - on the outside it is covered with short needles or spikes. Conventionally, these bizarre creatures can be divided into three groups: ordinary starfish; feather stars, named for their writhing rays (up to 50!), and "fragile" stars that cast their rays in case of danger.
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 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 nervous system organisms of interest to us. It is located partially in the skin epithelium or in the epithelium of invaginating parts of the body.
External structure
Characteristics of echinoderms should be supplemented by features external structure 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. Body sea urchins protected by a lime 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 ambulacral system serves for touch, movement, and in some sea urchins and sea lilies designed 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 emerges from it new organism. 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. Total number 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 this, however, in the Mesozoic and Paleozoic era 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. Common name edible holothurians - "trepang". Trepang is mined on a large scale in Far East. There are also poisonous holothurians. They make various medicines(for example, holothurin).
Currently, about 1150 species of sea cucumbers are represented. Their representatives are divided into 6 groups. Silurian- 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 species were introduced 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. Incidentally, using this food product associated with such a long life expectancy in this country, where people live an average of 89 years.
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.
