What type of invertebrate is a starfish. What type of invertebrate is the starfish? Sense organs in starfish

Everyone has seen the stars that can be seen every night in the night sky. In order to observe them, you need a telescope, since these stars are located very far from us.

However, there are stars that live next to us in the sea. We can easily observe these stars without a telescope. It is, of course, starfish.

Despite the fact that almost every person has seen a starfish at least once in his life, information about its biological features is little known to a wide audience. In the process of analyzing literary sources, it turned out that in encyclopedias about animals, information about these marine life presented quite a bit. That is why we turned to the study of highly specialized sources.

In the process of work, the following research methods were used:

1) theoretical, including analysis of sources of information; and

2) empirical - observation of the anatomical structure and behavior of the starfish.

1. 1. WHO ARE THE Echinoderms?

Sea stars belong to the type of echinoderms.

Echinoderms are headless animals whose body is divided into five rays. The ancestors of starfish inhabited the Earth about 580 million years ago. Over 13,000 species of extinct echinoderms have been discovered, and there are slightly more than 6,000 species living today.

Among modern echinoderms, five classes are distinguished:

➢ Sea lilies. This class includes animals resembling flowers. Their rays are branching.

➢ Sea capsules, or sea cucumbers. Their bodies are sac-like or worm-shaped.

➢ Sea urchins. This class includes animals with an almost spherical body shape.

➢ Starfish. As the name implies, this class includes animals with a body in the form of a star (five- or multi-beam).

The body dimensions of echinoderms usually range from 5 to 50 cm, but there are species whose length does not exceed a few millimeters, while in others, on the contrary, it can reach up to 5 m.

All echinoderms live in the sea. They are not found in fresh waters. They are called so because of the needles that cover the surface of their calcareous shell. However, only sea urchins can truly be called that. In animals of other classes, needles are found only in some parts of the body or are completely absent. Almost all echinoderms are able to move slowly with the help of suction cups on their legs.

1. 2. WHERE DO THE STARS LIVE?

Among the animals that have survived to this day, starfish are one of the most ancient groups. There are about 1,500 species of starfish on Earth, belonging to about 300 genera and 30 families. They are found in all oceans and salty seas- from the Arctic Ocean and the waters washing the coasts of Antarctica, to the tropical and equatorial zones of the ocean. In seas with normal salinity, starfish can be seen near the shore, so starfish were well known to man already in ancient times. Their images were found on frescoes found during excavations on the island of Crete; their age is over 4000 years. The very name aster, that is, a star, was given to these amazing animals by the ancient Greeks.

1. 3. WHAT "DRESS" IS THE STAR?

Starfish can be various shades of orange, pink and red. There are also stars painted in purple, blue, green, brown and even black. Sometimes the coloring is spotty, and various bright colors can form a bizarre pattern.

The typical dress cut for starfish is five points, but many species have six or more points. For stars living in Antarctic waters, the number of rays can reach 45, and for a solar star even 50! Sometimes the number of rays in stars of the same type is different. So, in a star that is common in our northern and Far Eastern seas, the number of rays ranges from 8 to 16.

1. 4. HOW ARE THE STARS?

Sea stars usually have a more or less flat body with a central disk gradually turning into rays or arms radiating from it. The downward side of the star with a mouth opening in the center is called oral, that is, oral, and the upper side is called aboral. Sometimes the oral side is conditionally called the ventral side, and the aboral side is called the dorsal side. In stars that have an anus, it is located near the center of the aboral side of the disk.

Sea stars have a primitive nervous system. They do not have any clearly defined brain cells. But the experiments of scientists show that some stars can develop conditioned reflexes.

1. 5. HOW MANY LEGS IS A STAR?

In the middle of the lower side of each ray there is a furrow, in which there are numerous soft mobile outgrowths, mobile tentacles - ambulacral legs with suckers at the end. They are connected to a system of channels through which water circulates under pressure. The legs are located mostly in two, and in some stars in four rows along the entire length of the beam. Their total number in each of the rays can reach several hundred. The ambulacral legs serve the starfish for locomotion and for breathing.

1. 6. HOW DO THE STARS “WALK”?

At first, it may seem that starfish are completely motionless. In fact, all adult starfish constantly crawl along the bottom surface or burrow into the sand, only very slowly. Such a leisurely lifestyle is explained by the fact that the muscles of the stars are relatively poorly developed.

Each leg is connected to an ampulla located inside the beam - a muscular sac in the form of a small bubble that can contract and stretch. As pressure increases, the ambulacral pedicles stretch and change direction in response to muscle contraction. The starfish moves through the coordinated movements of the ambulacral legs.

The thrust force developed by a star can reach several kilograms. Thanks to this, starfish manage to open bivalve shells. At first, the shell closes tightly, but it cannot live like this for a long time, because it needs fresh water to breathe, and its muscles get tired. And as soon as the gap appears, starfish stretches the shells of the mollusk and, turning its stomach outward, envelops the mollusk with it and begins to digest.

1. 7. WHERE IS THE STAR'S EYES?

Surprisingly, the starfish actually has eyes! Eyes are the only sense organs that are developed in starfish.

The last unpaired ambulacral leg of each ray is devoid of a sucker and is a short tentacle, at the base of which there is a red eye, consisting of numerous separate eye cups. With the help of the eyes, the star cannot "see" in the true sense of the word, but is only able to distinguish between the intensity of illumination and the direction of light. In addition to the unpaired terminal tentacle, several ambulacral legs adjacent to it may also lack suction cups and perform the function of touch. The creeping star pulls them forward and feels the surface with them.

1. 8. WHAT IS A STARFISH FOR DINNER?

Many stars, especially those that live in shallow waters, are predators. The Star Dinner consists of various molluscs, crustaceans, coelenterates and other invertebrates. Stars can also eat their own kind - echinoderms, for example, sea urchins.

1. 9. DOES THE STARFISH HAVE CHILDREN?

Yes there is. Most starfish are dioecious. But there are times when young stars are males, and grown to a certain size are females.

Sex cells are released into the water; fertilization takes place in water. The fertilized eggs develop into larvae that swim freely in the water. The larvae then attach themselves to rocks or the bottom and grow.

Many stars often show concern for offspring. Sometimes a star attaches eggs in sheltered places and then crawls away. However, among the inhabitants of cold waters or great depths, even the already formed young stars are hatched on the mother's body until they become independent.

Sea stars are very prolific. For example, Asterias rubens can release about 2.5 million eggs into the water in just 2 hours, and this can happen several times during the breeding season.

2. DESCRIPTION OF THE METHODOLOGY AND RESULTS OF THE STUDY

The research methodology consisted in using the method of direct observation, in particular, of the behavior and movement of the starfish on land and in the marine environment, as well as observing its structure. The observation was carried out for 4 hours.

This summer, my parents and I rested in the village of Plastun, which is located in the north of Primorsky Krai. Plastun is known as a sea and commercial port. Once we went on a boat to the sea to catch scallops and sea urchins. Vitaly Ivanovich Antonov, an amateur diver with 20 years of diving experience, put on a diver's suit and went down into the water to a depth of 25 meters. Thirty minutes later he surfaced and pulled out a net full of scallops and a few sea urchins. Then he dived a second time. When he appeared on the surface of the water, we saw huge tentacles of light orange color. When he swam closer, we saw that it was a starfish, but its size was enormous. In diameter, the star reached 50-60 centimeters! This is how I first met the starfish. We examined the starfish from all sides and took several pictures with the sea beauty. When we arrived at the port, we released our friend into the sea.

Our star belongs to the species Asterias rubens, that is, a red star.

This type of stars lives on rocks or stones, from shallow water to a depth of 650 m, and is common in the Baltic, North Seas and along the shores of the Atlantic Ocean.

Its size can reach a diameter of 12 to 40 cm. Thus, our friend was a giant!

The hallmarks of Asterias rubens are usually 5 thick rays; relatively small disc of the body; short needles. We could observe all these signs in our specimen. The length of the starfish rays in our case reached 50 cm.

We could also observe that there were furrows in the middle of the underside of each ray, in which there were ambulacral pedicles with suction cups at the end. The legs were arranged in four rows along the entire length of the beam.

The photo shows that in our case the color of the star on the oral side is light orange, the color of the aboral side is brick-reddish. The color of this type of star can be different - gray, yellowish, reddish or slightly purple.

The star feeds on snails, bivalves, sea urchins and crustaceans. Such a gigantic size of the star can probably be explained by a fairly rich diet in the habitat. Since, according to local residents, the area is known for a large number of scallops and sea urchins.

In the process of research, we could observe how the star moved with the help of its legs on land (on a boat). The ambulacral legs at the end of the beam were extended, as if feeling the surface, and then the body of the star contracted very slowly and thus movement took place. For 2.5 hours of travel, the star was able to move 20 cm.

When we tried to raise a star, it was not very easy. She strongly stuck to the surface of the boat and her traction force was quite large. An adult man barely managed to tear it off the surface. When we held it in our hands, it seemed that the star froze, it was completely motionless.

Upon returning to the port, we released our friend into the sea and watched her behavior. For some time, 20 minutes, the star remained motionless. However, the star then released its ambulacral legs, and it was clearly visible how it felt the surface with a single beam. This confirms the presence of peculiar organs of touch located at the tips of the rays of the starfish.

CONCLUSIONS: Thus, the observed specimen is a typical representative of starfish belonging to the species Asterias rubens, which corresponds to all the anatomical characteristics of this species. The exception is the size of the starfish, which exceeds the standard parameters for stars of this type. Presumably big size of the observed specimen is explained by favorable habitat and nutritional conditions. During the study, we observed anatomical structure starfish, as well as the features of its movement in various environments. The way the starfish moves is confirmed by the fact that there are special organs of touch and vision located at the ends of the rays.

CONCLUSION

This work was aimed at studying biological features and lifestyle of the starfish. In the course of the study, a review of the literature on the biological and anatomical features of the starfish, its habitat, nutrition and reproduction was carried out. During the observation, the ways of moving the starfish in different environments were studied. The results of the study are presented in the form of a presentation.

Sea stars - animals with unusual shape body, thanks to which they attracted the attention of people in ancient times. Sea stars belong to the phylum Echinodermata, in which they are isolated in separate class, numbering almost 1600 species. The closest relatives of these invertebrates are the ophiurs, or serpenttails, which are very similar to them, and the more distant holothurians and sea urchins.

home distinguishing feature starfish is, of course, the shape of the body. In general, the body of starfish can be divided into a central part - a disk, and lateral outgrowths, which are commonly called rays or arms. These animals are characterized by radial symmetry, so their body is divided into symmetrical sectors, the number of which is usually five. However, among starfish there are organisms with a large number axes of symmetry: in some species their number can reach 6-12 and even 45-50.

Nine-armed starfish (Solaster endeca).

Each sector, respectively, includes a part of the central disk and a hand. It would seem that such a structure of the same type should result in the uniformity of these living organisms. But just the shape of the body of starfish is very variable. First, the relative length and thickness of the rays varies greatly: in some species they are elongated and thin, in others they have a triangular shape, sharply tapering towards the end, in others the rays are so short that they practically do not protrude beyond the edges of the central disk. The stars of the last type have a very high central disk, so they resemble pillows. Thus, in most types of starfish, the length of the rays is 3-5 times greater than the diameter of the central disk, in the longest-armed ones it is 20-30 times, and in pillow-shaped ones it tends to zero.

This bright ottoman seabed in fact, the New Guinean culcita starfish (Culcita novaeguineae).

Secondly, starfish differ in surface texture and color. Here the variety simply defies description - smooth, spiny, prickly, rough, velvety, mosaic; monochrome and patterned, bright and faded. The color scheme of these animals includes almost all colors, but most often there are various shades of red, less often blue, brown, pink, purple, yellow, black. Pale starfish usually live in deep water, while shallow water species are bright.

This is the same New Guinea culcite, but of a different color.

At first glance, starfish seem primitive, because they do not have any noticeable sensory organs, brain, internal organs are poorly differentiated, but this simplicity is deceptive.

Linkia starfish (Linckia laevigata) is bright blue in color, its rays look like sausages.

First of all, it should be noted that starfish have an internal skeleton. They do not have a backbone and separate bones, but there are many calcareous plates connected to each other in an openwork system.

Openwork plexus of skeletal elements on the surface of a starfish.

In a young starfish, the skeletal elements are hidden under the skin, but over time, the skin over some of the calcareous spines is erased and they become visible from the outside. It is these spines that give starfish their spiky appearance.

The spikes on the surface of the starfish are covered with skin, but some of them are already exposed and have a shiny surface.

In addition, calcareous plates can be seen on the upper side of the body in many species, fused together or forming a network.

A bizarre pattern formed by the skin and skeletal elements of the starfish.

Finally, the third element that affects the appearance of the starfish is pedicellaria. Pedicellaria are modified needles that look like tiny tweezers. They play an important role in the life of the starfish, with their help it cleans the upper side of the body from debris and sand. All skeletal elements are interconnected by muscles, therefore, after the death of a starfish, its skeleton crumbles into lime plates and there is not a trace left of the animal.

The starfish acanthaster, or the crown of thorns (Acanthaster ellisii) has prickly and poisonous thorns.

The muscular system of starfish is relatively poorly developed. Each ray has a muscle cord that can bend the ray upwards, and this, in fact, is what the muscle movements of the stars are limited to. But mobility is not limited at all. Starfish can crawl, dig, bend, swim, but they do not do this with the help of muscles.

Starfish scalloped patiria (Patiria pectinifera) climb algae.

These animals have a special body system - ambulacral. In essence, this system is channels and cavities connected together and filled with liquid. The starfish can pump this fluid from one part of the system to another, causing its body parts to bend and move. The centerpiece of this system is the ambulacral pedicles, tiny blind outgrowths of the ambulacral canals on the underside of the starfish. Each leg moves independently of the others, but their actions are always coordinated. With the help of these microscopic elements, the starfish can work wonders. For example, it is able to climb a vertical surface, it can stick to the glass of an aquarium for a long time, it can stand on its hind legs, swelling up like an angry cat, or it can, grabbing two beams, push the shells of a mollusk apart. And all this is done by an animal practically devoid of a brain and eyes!

On the underside of the beam, translucent ambulacral pedicles are visible.

In fairness, it should be noted that starfish still have some sense organs. These are eyes located at the ends of each beam. The eyes are very primitive and distinguish only between light and darkness; starfish do not see objects. Sea stars are able to catch chemical substances(analogous to scent), only now they feel them differently. Some species are very sensitive and can crawl to the bait by smell for several days in a row, others can crawl past the victim a couple of centimeters and not smell it. Sea stars have a very developed sense of touch, they try to get rid of the sand that fills them from above, and they also always try to feel their way with the help of small tentacles at the end of each beam. The sense of touch tells the starfish whether it is a prey or a predator. The brain of a starfish is replaced by a group of loosely interconnected cells. Surprisingly, despite such a primitive structure nervous system starfish can develop elementary conditioned reflexes. For example, starfish that were often caught in nets began to get out of them faster than those that were caught for the first time.

At the end of the ray of the starfish asterodiscus (Asterodiscus truncatus) a decorated eye is visible. The beam itself is covered with relief lime plates.

Another "strong", directly and figuratively words, the system of starfish is the digestive system. The mouth of these animals is located in the center of the disc on the underside, and the tiny anus is on the dorsal side of the body. By the way, starfish rarely use it (in some species, it generally overgrows), preferring to remove food debris through the mouth. The stomach of starfish has outgrowths extending into rays; reserves are deposited in these outgrowths. nutrients in case of hunger. And starfish starve regularly, because during breeding they stop eating. The stomach in many species can turn outward through the mouth opening, and it stretches like rubber, taking any shape. Thanks to the expandable stomach, the starfish can digest prey that is larger than it is. A case is known when the starfish luidia swallowed such a large sea urchin that it died, unable to spit out its remains.

In the middle of the central disk of fromia monilis, a tiny anus is visible.

Other body systems are poorly developed in starfish. They breathe through special outgrowths of the skin on the upper side of the body washed by sea currents. They do not have gills and lungs, so starfish are sensitive to lack of oxygen. They also cannot stand desalination, so they are found only in the seas and oceans. The sizes of starfish range from 1-1.5 cm for the miniature globular star Podosferaster to 80-90 cm for the Freyella starfish.

The name of this starfish speaks for itself - elegant fromia (Fromia elegans).

Sea stars have a global distribution. They are found everywhere in all seas and oceans from the tropics to the poles. Of course, species diversity is higher in warm waters than in cold ones. Most species prefer to live in shallow waters, some even end up on the shore at low tide. But among these animals there are also deep-sea species, including those that live at depths of more than 9 km!

Sea stars in shallow water.

Starfish crawl along the bottom most of the time, they do it very slowly, the usual speed of a medium-sized starfish is 10 cm per minute, but a starfish can also “hurry up” at a speed of 25-30 cm per minute. If necessary, starfish can climb rocks, corals, algae. If a starfish falls on its back, then it immediately turns over with its ventral side down. To do this, the animal bends two rays so that the ambulacral legs on the lower side touch the ground, and then the starfish twists its body and assumes its usual position. Some species are even able to clumsily swim short distances. Sea stars can be called sedentary animals, the marking of animals showed that they do not move more than 500 m from the place of the initial catch.

The starfish granular coriaster (Coriaster granulatus) looks like a bun.

Despite the outward primitiveness and seeming helplessness, starfish are formidable predators. They are quite gluttonous and never refuse prey, except for the period of gestation of eggs. Only deep-sea species feed on silt, from which they extract food particles; culcite starfish, which prefer to nibble on coral fouling, can also be called conditionally “non-predatory”. All other species actively hunt other animals.

A completely non-romantic relationship began between the starfish (Solaster dawsoni) and the spiny hippasteria (Hippasteria spinosa).

Most starfish are not picky, they eat everything they can hold with their hands and what their “rubber” stomach can get, without disdaining carrion. Some species can only eat a certain type of food: sponges, corals, gastropods.

Pretty starfish pentagonaster (Pentagonaster pulchellus), which is also called the biscuit starfish for its biscuit-like body shape.

The favorite prey of sea stars are sedentary animals like themselves - sea urchins and bivalve molluscs. The star overtakes the sea urchin by crawling and eats it with its mouth. Bivalve mollusks have shells that close tightly when threatened, so starfish treat them differently. First, the starfish is glued with two rays to the shell valves, and then begins to push them apart. I must say that the ambulacral legs are firmly glued to the substrate due to the adhesive lubricant and one single ambulacral leg can develop a force of up to 30 g! And there are hundreds of them on each ray of a starfish, so the star, like a real strongman, pushes the shells apart with a force of several kilograms. However, the starfish does not need to push the shell flaps to its full extent; for a hearty dinner, a gap of 0.1 mm is enough for it! In this truly microscopic gap, the starfish twists its stomach (it can stretch 10 cm) and digests the mollusk in its own home.

Asteria starfish (Asterias rubens) stretches its hand towards a mollusk.

Most sea stars have separate sexes, very few species have both male and female gonads. The gonads are arranged in pairs at the base of each ray. In the starfish asterina, young individuals are first male, and then change it to female. A special exception is the ophidiaster starfish, which has no males ... at all. Females of this species lay eggs without fertilization, such reproduction is called parthenogenesis. During mating, males and females combine their rays and sweep sperm and eggs into the water. The number of eggs depends on the type of development of the larvae and ranges from 200 in those species that bear offspring, and up to 2-200 million in species with free-swimming larvae.

Mating starfish.

Starfish larvae come in three types. In some species, a free-swimming larva hatches from the eggs, which feeds on microscopic algae, and then attaches to the bottom and gradually turns into a small star. In others, the free-swimming larva has a large supply of yolk, so it does not feed and immediately transforms into an adult form. In starfish that live in cold waters, the larvae do not separate from the mother's body at all, but accumulate near her mouth or even in special stomach pockets. A caring female during this period relies only on the tips of the rays, and the body arches in a dome, under which the larvae are located. Since the larvae are located near the mouth opening, the female does not feed during this period. The larval form is the most mobile in life cycle starfish, it is during this period that the larvae can be carried by currents over very long distances.

The starfish larva is bilaterally symmetrical.

In addition to sexual reproduction, starfish can also reproduce asexually. Most often this occurs in multi-beam species, the body of the animal is divided into two halves, each of which builds up the missing rays. In other species, asexual reproduction may be the result of regeneration after traumatic injury to the body. If a starfish is artificially divided into several parts, then a new organism will form from each. Even one beam is enough to restore, but a piece of the central disk is required. Sea stars grow slowly, so for many months they look one-sided.

The seagull caught a starfish.

But the starfish astropecten is friends with polychaete worms. Up to five cohabitants can be found on one star, who prefer to stay on the underside of the body closer to the star's mouth. The worms pick up the remains of the star's prey and even ... put their head in her stomach. A special type of ctenophores live on the Echinaster starfish, which clean the surface of the star from fouling.

These bright spots on the Luzon starfish (Echinaster luzonicus) are ctenophores (Coeloplana astericola).

Since ancient times, people have paid attention to the colorful animals of shallow water, but starfish have not been of any economic interest to them. Only in China, starfish are sometimes eaten, while feeding starfish to pets can lead to their death. This is likely due to the toxins that some species accumulate by eating corals and poisonous molluscs. But with the development of the marine economy, people began to classify starfish as their enemies. It turned out that starfish often eat the bait in bottom crab traps, and also raid oyster and scallop plantations. In a few years (that's how many oysters need to be grown), starfish can destroy an entire oyster jar. At one time, they tried to destroy starfish by cutting them into pieces, but this only increased their numbers, because a new starfish grew from each stump. Then they learned how to extract starfish with special trawls and kill them with boiling water.

Very spectacular mosaic starfish (Iconaster longimanus).

by the most malicious pest turned out to be the starfish acanthaster, or the crown of thorns. This very large starfish feeds exclusively on corals, after which the crown of thorns leaves only a white lifeless path on the coral reef. At one time, these stars multiplied so much that they literally destroyed a huge section of the Great barrier reef off the coast of Australia. The unique geological formation was under the threat of destruction. The fight against the crown of thorns was complicated by the fact that its thorns are poisonous to humans, the prick of the crown of thorns causes burning pain, although not fatal. Specially trained divers collected acanthasters with sharp spikes in bags or injected a lethal dose of formalin into the body of a starfish. Only in this way it was possible to pacify the invasion of voracious predators and save the reef. Now all types of starfish are in a safe condition and do not need protection.

The crown of thorns eats the coral.

Sea stars are echinoderm invertebrates. The top of the starfish consists of a protective outer shell, below is a mouth and numerous ambulacral legs, which the star uses for locomotion and feeding. Most stars reproduce sexually, but asexual reproduction is also quite common.
Let's dwell on the methods of reproduction in more detail!

Damaged starfish regenerate very easily, rebuilding lost arms and damaged disk parts. Species of the genus Asterias can throw off their arm when injured. Experiments on Asterias vulgaris show that regeneration of the entire star can take place if there is one arm and one fifth of the central disk. If the disc fragment includes a madrepore plate, then regeneration will be successful even if there is less than a fifth of the disc. Once the disc and intestines are restored, the animal is able to resume feeding even before the intestines and hands are completely regenerated. Completion of regeneration is slow and sometimes takes a whole year to complete.

For some starfish, reproduction by splitting apart is the normal form of asexual reproduction. At the same time, softening of the connective tissue occurs in the division plane. The most common form of fission is the splitting of a star in half. Each half then regenerates the missing portions of the disk and arms, although extra arms often appear along the way. Species of the starfish genus Linckia, common in the Pacific Ocean and other areas of the World Ocean, are unique in their ability to throw off their arms entirely. Each individual hand, if not eaten by a predator, can regenerate a new body. Some starfish species reproduce clonally in the larval stage. They develop buds on their larval arms, which differentiate into new larvae.
With a few exceptions, starfish are dioecious. The ten gonads, two in each arm, resemble bunches or bunches of grapes. In non-breeding individuals, the gonads are wrinkled and occupy the bases of the arms. However, the gonads of sexually mature specimens fill the arms almost completely. Each gonad releases gametes through its own gonopore, usually located between the bases of the arms, although the gonopores of some starfish open sequentially along the arms or on the oral surface. There are several hermaphroditic species. These species include, for example, the common European starfish Asterina gibbosa, which is a protandrous hermaphrodite. Most starfish hatch eggs and sperm into sea ​​water where fertilization takes place. They usually breed once a year and a single female can lay 2.5 million eggs.

Most starfish have hatched eggs and subsequent developmental stages are planktonic. Some starfish, especially cold-water species, incubate large, yolk-rich eggs under an arched body, in aboral disk pockets, in brooding baskets formed by needles between the bases of the arms, under the paxilla, or even in the cardial stomach. In all species that bear eggs, development is direct. Asterina gibbosa is not an egg-bearing species, although it attaches its eggs to rocks and other objects, which is also unusual for this group of animals.

Development

Starfish embryos in most cases hatch from eggs and begin to swim at the blastula stage. The coelom arises from the terminal part of the developing primary gut as two lateral sacs that extend backward towards the blastopore (= anus). A small tubular process of the left coelom (protocoel + mesocoel = axohydrocoel) opens on the dorsal surface as a hydropore, which is a larval nephridiopore. By the time of the formation of the coelomic cavities and intestines, the larvae of the cilia in the integument are concentrated within the ciliary cord. It is a curved strip that runs along the surface of the larva, and later rises to outgrowths - the larval arms. Eventually, the anterior ventral part of the ciliary cord separates from the rest and forms a separate preoral loop. At this stage, the bilaterally symmetrical larva feeding on food suspended in the water column is called a bipinnaria.

The ciliated cords serve both for locomotion and feeding, while the larval arms increase their area. Phytoplankton and other tiny food particles are collected and thrown away in the opposite direction of the beating of cilia and then transported to the mouth.
Bipinnaria becomes brachiolaria with the appearance of three additional arms at the anterior end. These short arms (brachioles), ventral in location, bear adhesive cells at their ends. Between the bases of the hands is a glandular adhesive disc, or sucker. Three hands and an adhesive disc are used to attach when sinking to the bottom. As a rule, it is the brachiolaria that is the larval stage that sinks to the bottom and undergoes metamorphosis, however, in some starfish, such as Luidia and Astropecten, settling occurs at the bipinnaria stage.
Metamorphosis

When starfish larvae are ready to settle to the bottom, their positive phototaxis changes to negative. When settling, the brachiolaria is attached with its front end to the bottom with the help of brachioles and suckers, which form an attachment stalk.
During metamorphosis, a bilaterally symmetrical larva turns into a pentameric juvenile. In this case, the loss and reconstruction of larval tissues and the morphogenesis of new structures occur, and the rudiment of a juvenile star is formed behind on the left side of the body. In this case, the left side of the body of the larva becomes the oral surface, and the right side becomes the aboral. Part of the larval intestine is retained in the juvenile, but the larval mouth and anus are lost and subsequently formed anew in their new positions. The right larval mesocoel degenerates, but the left protomesocoel (axohydrocoel), including the pore canal and hydropore, is preserved and modified into the SCC. The arms of the juvenile star are new processes of the body wall, not connected with the larval arms. Eventually, a young starfish, less than 1 mm in diameter, separates from the larval stalk and crawls away on short arms:
Growth rates and lifespans of starfish vary widely, as demonstrated by observations of two species of the intertidal zone of the Pacific coast of the United States. Leptasterias hexactis bears a small number of yolk-rich eggs during the winter, and juveniles become sexually mature at the age of two years, when their weight reaches about 2 g. The average lifespan of this species is 10 years. Pisaster ochraceus produces large numbers of eggs each spring and development is planktonic. Sexual maturity is reached by the age of five with an animal weight of 70 to 90 g. Individuals can live for 34 years, breeding annually.

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 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 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 habitat of sea stars is also wide - from the surface layers of the sea to kilometer depths, although, of course, at great depths, the species diversity and number of starfish is more scarce.
AT Russian seas There are about 150 species of starfish that 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 starfish are known, whose appearance 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. Here may be the most various 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, 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 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 starfish.

natural enemies sea ​​stars do not. 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, 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 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 loves to eat very much. coral polyps, thus 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 seabed orderlies, eating carrion and the remains of the 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.