Starfish structure. Starfish class
If you find yourself in the Dominican Republic, don’t miss the chance to visit the Blue Lagoon and get acquainted with its beautiful and unusual inhabitants - starfish. You will find shocking facts about these creatures in this article!
Starfish are not just beautiful decorations and decoration of the seabed. At first glance, they seem primitive and somehow unreal. But appearances are deceiving. These animals have a complex nervous and digestive system.
Well, for example: did you know that the starfish is a real predator? And stars can move along the seabed over considerable distances. And this is not all that is known about starfish.
Facts about starfish
We have collected for you the most interesting facts about these amazing animals.
According to the texture of the body surface, starfish are:
- smooth
- spiky
- prickly
- rough
- velvety
- mosaic
- plain and patterned
- bright and faded
Starfish come in a wide variety of colors. Most often this
- various shades of red
- blue
- brown
- pink
- violet
- yellow
- black
The deeper the sea star's habitat, the paler it is. Those individuals that live in shallow waters are distinguished by the brightest colors.
Food and hunting
Starfish have a kind of sense of smell - they are able to detect chemicals. This helps them hunt.
Yes, yes - most starfish are real predators!
Here are just some of the inhabitants of the seabed that the stars hunt:
- shellfish
- crustaceans
- plankton
- sponges
- corals
- gastropods
- other invertebrates, including echinoderms. For example, sea urchins are one of the starfish’s favorite delicacies.
The process of hunting, absorption and subsequent digestion of prey requires a separate story. We advise the faint-hearted and impressionable to scroll through these details.
The starfish is not picky about food and eats everything it can digest. She does not disdain carrion.
On the abdomen of the starfish there is a mouth through which it absorbs prey. If any mollusk becomes its victim, then the starfish crawls onto it and sticks with its rays to its valves. Thanks to the adhesive lubricant, the star manages to stick very firmly to the shells of the mollusk.
After this, a long struggle begins: the mollusk squeezes the valves of its shell, protecting itself from the predator, and the star strives to open them to gain access to the contents.
As a rule, the outcome of this confrontation is disastrous for the mollusk: the starfish is much stronger. And besides, for a hearty lunch, a gap of only 0.1 mm is enough for her!
Then something fantastic happens: the starfish turns out its stomach, which can stretch up to 10 centimeters! The stomach penetrates the shell of the mollusk, where the entire digestive process takes place, lasting several hours.
Thanks to its expandable stomach, the starfish can even digest prey that is significantly larger than its size. There is a known case where a starfish died after swallowing a sea urchin so large that it could not spit out the remains.
Reproduction
Starfish reproduce in different ways:
- Reproduction by regenerative means.
Due to the softening of the connective tissue, the starfish breaks up into several parts or casts off its rays. Then full-fledged stars grow from these parts.
- Sexual reproduction.
In a starfish, the gonads are located in pairs at the base of each ray. During mating, males and females connect their rays and release sperm and eggs into the water.
Those species of starfish that bear offspring lay 200 or more eggs.
Female starfish, whose larvae are free-swimming, are capable of laying up to 200 million eggs!
Among starfish there are also unisexual species. The bodies of such stars produce both male and female reproductive products. They carry their offspring in a brood pouch or special holes on their back.
And there are also species that during their lives change sex from male to female (for example, the asterine starfish).
There are three types of starfish larvae:
- in one type of star, the egg hatches into a larva that swims freely and feeds on tiny pieces of algae. After a few weeks, it attaches to the bottom and gradually turns into a small star with a diameter of 5 centimeters.
- in another type, the larva has large reserves of yolk, which allows it to do without additional nutrition and grow into an adult star
- in those stars that live in cold waters, the larvae remain on the mother’s body and concentrate around her mouth. Therefore, during this period, the female has to do without food and move very, very carefully, arching her body so as not to harm the larvae.
The size of the larvae usually does not exceed 3-5 mm
Starfish larvae can be carried over enormous distances by currents.
The starfish becomes sexually mature only at the age of 2-3 years.
The starfish is almost invulnerable. It is protected from natural enemies by:
- sharp thorns (sometimes poisonous)
- ability to bury itself in sand in case of danger
- shrimps
- shellfish
- polychaete worms
They settle on the back of the starfish and cause damage to its covering. The star herself tries by all means to get rid of uninvited guests.
Benefits for the eco system
Starfish have a positive effect on the ecology of the oceans and the planet as a whole:
- absorb and utilize carbon dioxide, harmful to the planet, which is becoming more and more in the Earth’s atmosphere every year
- are orderlies of the seabed, eating carrion and the remains of dead marine organisms, as well as weaker and sicker individuals of marine animals
Some of the most colorful and beautiful representatives of this species live near the southern coast of the Dominican Republic. You can get to know them by visiting the Blue Lagoon. A visit to this natural pool, located right in the middle of the Caribbean Sea, is included in all excursions to the island of Saona.
The Blue Lagoon, as well as the islands of Saona, Catalina and Catlinita are part of the Eastern National Park. And all the nature in these territories is carefully protected.
The lives of starfish are also protected. In order to preserve the population of this species, as of October 2017, it was prohibited to remove starfish from the water. And yet, starfish, as before, decorate the bottom of the water area and no one will stop you from admiring them.
Let's take care of nature and the fragile lives of starfish!
And then everyone will be pleased to return to the Blue Lagoon again and again to visit their old star acquaintances.
They raise many questions, among which the following are of particular interest: “What does a starfish eat?”, “For whom does it pose a mortal threat?”
Stars on the seabed
These extraordinary decorations of the seabed have existed on the planet for quite a long time. They appeared about 450 million years ago. There are up to 1600 types of stars. These animals inhabit almost all seas and oceans of the earth, the water of which is quite salty. Stars do not tolerate desalinated water; they cannot be found in the Azov and Caspian Seas.
Animals can have rays from 4 to 50, sizes range from a few centimeters to a meter. The lifespan is about 20 years.
The sea inhabitants do not have a brain, but on every ray there is an eye. The organs of vision resemble insects or crustaceans and distinguish between light and shadow well. Many eyes help animals hunt successfully.
Stars breathe almost through their skin, so it is very important for them to have a sufficient amount of oxygen in the water. Although some species can live at decent depths of the ocean.
Structural features
It is interesting how starfish reproduce and feed. Biology classifies them as invertebrate echinoderms. The starfish does not have blood as such. Instead, the star's heart pumps sea water enriched with certain microelements through its vessels. Pumping water not only saturates the animal's cells, but also by forcing fluid into one place or another helps the star move.
Starfish have a ray structure of the skeleton - rays extend from the central part. The skeleton of sea beauties is unusual. It consists of calcite and develops inside a small star from almost a few calcareous cells. What and how starfish feed largely depends on the characteristics of their structure.
These echinoderms have special pedicellaria on their tentacles in the form of tweezers at each tip of the outgrowth. With their help, the stars hunt and clean their skins from debris clogged between the needles.
Cunning hunters
Many people are interested in how starfish eat. A brief description of the structure of their digestive system can be found below. These amazing beauties create the impression of complete security. In fact, they are sea predators, voracious and insatiable. Their only drawback is their low speed. Therefore, they prefer a stationary delicacy - mollusk shells. The starfish eats scallops with pleasure, and is not averse to eating sea urchins, sea cucumbers, and even fish that carelessly swim too close.
The fact is that the starfish has practically two stomachs, one of which can turn outward. An unwary prey, captured by the pedicellariae, is transferred to the mouth opening in the center of the rays, then the stomach is thrown over it like a net. After this, the hunter can release the prey and slowly digest it. For some time, the fish even drags its executioner along with it, but the victim can no longer escape. Everything that a starfish eats is easily digested in its stomach.
She acts somewhat differently with shells: she slowly approaches the dish she likes, entwines the shell with her rays, places her mouth opening opposite the slit of the shell and begins to move the shells apart.
As soon as even a small gap appears, the external stomach is immediately pushed into it. Now the sea gourmet calmly digests the owner of the shell, turning the mollusk into a jelly-like substance. This fate awaits any eaten victim, no matter whether the starfish feeds on a scallop or a small fish.
Features of the structure of the digestive system
The predator does not have any devices for capturing prey. The mouth, surrounded by a ring lip, connects to the stomach. This organ occupies the entire interior of the disc and is highly flexible. A gap of 0.1 mm is enough to penetrate the shell doors. In the center of the aboral side, a narrow, short intestine opens, extending from the stomach. What a starfish eats largely depends on the unusual structure of its digestive system.
Love of the stars at the bottom of the ocean
Most starfish are heterosexual. During love games, individuals are so busy with each other that they stop hunting and are forced to fast. But this is not fatal, because in one of the stomachs these cunning creatures try to deposit nutrients in advance for the entire duration of mating.
The gonads are located in stars near the base of the rays. When mating, the female and male individuals connect the rays, as if merging in a tender embrace. Most often, eggs and male reproductive cells end up in sea water, where fertilization occurs.
If there is a shortage of certain individuals, stars can change sex to maintain the population in a certain area.
These eggs are most often left to their own devices until the larvae hatch. But some stars turn out to be caring parents: they carry eggs and then larvae on their backs. For this purpose, in certain species of starfish, during mating, special sacs for eggs appear on their backs, which are well washed with water. There she can remain with the parent until the larvae appear.
Reproduction by division
A completely extraordinary ability of starfish is reproduction by fission. The ability to grow a new ray arm exists in almost all animals of this species. A star grabbed by a beam by a predator can throw it away like a lizard's tail. And after a while, grow a new one.
Moreover, if a small particle of the central part remains on the beam, after a certain time a full-fledged starfish will grow from it. Therefore, it is impossible to destroy these predators by cutting them into pieces.
Who are starfish afraid of?
Representatives of this class have few enemies. Nobody wants to mess with the poisonous needles of sea celestials. Animals are also able to secrete odorous substances to scare away particularly voracious predators. In case of danger, the star can bury itself in silt or sand, becoming almost invisible.
Among those who feed on starfish in nature, large seabirds predominate. On the shores of warm seas they become prey for seagulls. In the Pacific Ocean, cheerful sea otters are not averse to feasting on the star.
Predators harm underwater plantations of oysters and scallops - what the starfish eats. Attempts to kill animals by cutting them into pieces led to an increase in the population. Then they began to fight them, bringing the stars ashore and boiling them in boiling water. But there was nowhere to use these remains. There have been attempts to make fertilizer from animals that also repels pests. But this method was not widely used.
Starfish are veterans of the seabed, they appeared more than 450 million years ago, ahead of many forms of modern inhabitants of the underwater depths. They belong to the class Echinoderms, being relatives of sea cucumbers, brittle stars, sea lilies, sea cucumbers, sea urchins - currently there are about 1600 species of them, having a star-shaped or pentagonal shape.
The starfish, despite its inactivity and the absence of a head as such, has a well-developed nervous and digestive system. Why, exactly, “echinoderms”? It's all about the hard skin of the starfish - on the outside it is covered with short needles or spines. 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 off their rays in case of danger.
True, it will not be difficult for this animal to grow new ones, and new stars will soon appear from each ray. How is this possible? - Due to the characteristic feature of the star’s structure, each of its rays is structured in the same way, and contains: two digestive outgrowths of the stomach, performing the function of the liver, a red eyespot at the tip of the ray, protected by a ring of needles, radial bundles of nerves, olfactory organs (they are also suckers and a method of movement), papules located in a groove on the ventral side - skin gills in the form of thin short villi, processes of the genital organs located on the back and producing gas exchange (usually two gonads on each ray), a skeleton consisting of a longitudinal row of vertebrae inside, and hundreds of calcareous plates with spines, covering the skin and connected by muscles, which not only protects the animal from damage, but also makes its rays very flexible. The bodies of starfish are 80% calcium carbonate.
Thus, each ray of a starfish, once separated from its body, is completely viable and quickly regenerates. Well, connected together, the rays form closed systems in the center of the animal: the digestive system passes into the stomach from two sections and opens with a button-shaped disk, which serves as the mouth; bundles of nerves unite into a nerve ring. The main system of the starfish, which we deliberately left “for dessert,” is the ambulacral system. This is the name given to the water-vascular system, which serves the echinoderm simultaneously for respiration, excretion, touch and movement, together with the muscles providing musculoskeletal function. Canals extend from the perioral ring into each ray, from them, in turn, lateral branches to hundreds of cylindrical tubes on the surface of the body - ambulacral legs containing special ampoules and ending with suction cups. An opening on the back, called the mandreoporous plate, serves to connect this system to the external aquatic environment.
So how does the ambulacral system work? - It is filled with water under slight pressure, which, entering through the mandreoporous plate into the perioral canal, is divided into five ray channels and fills the ampoules at the base of the legs. Their compression, in turn, fills the legs with water and stretches them. In this case, the suckers of the legs attach to various objects of the seabed, and then sharply contract, the ambulacral legs are shortened, and thus the animal’s body moves in smooth jerks.
Starfish are voracious predators, although there are exceptions in the form of herbivorous species that feed on algae and plankton. In general, the favorite delicacies of these animals are clams, mussels, oysters, scallops, littorinas, barnacles, reef-forming corals and various invertebrates. The star finds prey by smell. Having discovered a mollusk, it attaches itself with two rays to one shell valve, and the remaining three to the other valve, and a many-hour struggle begins, which the starfish always wins. When the mollusk gets tired and the doors of its home become pliable, the predator opens them and literally throws its stomach onto the victim, turning it outward! By the way, food digestion occurs outside the animal’s body. Some starfish are even capable of digging out prey hiding in the sand.
As for reproduction, most starfish are divided into males and females. Fertilization occurs in water, after which free-swimming larvae called brachiolaria are formed. Unlike adult individuals, their structure is subject to the laws of symmetry, and includes a ciliary cord necessary for collecting food particles (exclusively unicellular planktonic algae), a stomach, esophagus and hind intestine. Usually the larvae swim near an adult sea star of the same species - and after several weeks, under the influence of its pheromones, they undergo metamorphosis: having fixed themselves on the bottom, they turn into tiny (0.5 mm in diameter), but already five-linked sea stars. But these babies will be able to give birth only after two or three years. If the larvae perform the function of dispersing species, and drift over long distances, they are able to delay their transformation into adults and not settle to the bottom for several months - and they can grow up to nine cm in length. Among the starfish there are also hermaphrodites - they carry their young in a special brood pouch or cavities on their backs.
Taking into account the large number of starfish, it is clear that they also influence the growth of populations of the species that are hunted. Nobody risks hunting them, since their bodies contain extremely toxic substances - asteriosaponins. Being virtually invulnerable, starfish are at the top of the marine food pyramid and can therefore have a lifespan of up to 30 years. If you believe scientists, then these brightly colored legendary inhabitants of the seas also make a significant contribution to the process of recycling carbon dioxide, including those produced by industrial facilities on the planet - their share is about 2% of CO2, that is, more than 0.1 gigatons of carbon per year, which, you see, is not weak at all for such seemingly small creatures!
Echinoderms are peculiar animals. They cannot be compared in structure with other types. These animals resemble a flower, a star, a cucumber, a ball, etc.
History of the study
The ancient Greeks gave them the name “echinoderms.” Representatives of this species have long been of interest to humans. 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 colibranchids. Mechnikov showed that these organisms are closely related to representatives of chordates.
Diversity of echinoderms
Nowadays, 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, the main part 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 possess among modern species.
Internal structure
Representatives of echinoderms develop a skeleton in the subcutaneous connective layer, consisting of calcareous plates and needles, spines, etc. on the surface of the body. Like chordates, in these organisms the secondary body cavity is formed by separation of mesodermal sacs from the intestine. During their development, the gastropore becomes overgrown or transforms into the anus. In this case, the larva's mouth is formed anew.
Echinoderms have a circulatory system. However, their respiratory organs are rather poorly developed or absent altogether. It is necessary to briefly describe other characteristics of echinoderms. These animals do not have special nervous systems of the organisms that interest us. The nervous system is quite primitive. It is located partially in the skin epithelium or in the epithelium of invading areas of the body.
External structure
The characteristics of echinoderms should be supplemented by the features of the external structure of these organisms. The outer epithelium of the majority of echinoderms (with the exception of holothurians) has cilia, which create a flow of water. They are responsible for supplying food, gas exchange and cleansing the body of dirt. In the integument of echinoderms there are various glands (causing luminescence and poisonous) and pigments that give amazing colors to these animals.
The skeletal elements of sea stars are calcareous plates, which are arranged in longitudinal rows, usually with spines protruding outward. The body of sea urchins is protected by a calcareous shell. It consists of a series of plates tightly connected to each other, with long needles sitting on them. Holothurians have calcareous bodies that are scattered across their skin. The skeleton of all these organisms is internal in origin.
Musculature and ambulacral system
The musculature of these animals is represented by muscle stripes and individual muscles. It is developed quite well, to the extent that this or that animal is mobile. In most species of echinoderms, the ambulacral system serves for touch and movement, and in some sea urchins and crinoids it is used for respiration. These organisms are dioecious; they develop with larval metamorphosis.
Classification of echinoderms
There are 5 classes of echinoderms: Brittle stars, Starfish, Sea urchins, Sea lilies and Holothurians. The phylum is divided into 2 subphyla: freely moving echinoderms are represented by brittle stars, holothurians, sea urchins and starfish, and attached ones - by crinoids, as well as some extinct classes. About six thousand living species are known, as well as twice that number of extinct ones. All echinoderms are marine animals that live only in salt water.
Sea stars
The most famous representative of the type we are interested in is the starfish (a photo of one of them is presented above). These animals belong to the class Asteroidea. It is no coincidence that starfish received this name. In their shape, many of them are a five-pointed star or a pentagon. However, there are also types whose number of rays reaches up to fifty.
Look what an interesting body the starfish has, the photo of which is presented above! If you turn it over, you can see that from the underside of the rays there are rows of small tube legs with a suction cup at the end. The animal, moving through them, crawls along the seabed and also climbs vertical surfaces.
All echinoderms have the ability to quickly regenerate. In a starfish, every ray that has separated from the body is viable. It immediately regenerates and a new organism emerges from it. Most starfish feed on leftover organic matter. They find them in the ground. Their diet also includes fish corpses and algae. However, some representatives of sea stars are predators that attack their prey (stationary invertebrates). After the prey is found, these animals dump their stomachs 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 valves of the mollusk. Starfish can, if necessary, crush its shell.
The most famous among them is Acanthasterplanci - crown of thorns. It is the worst enemy of marine coral reefs. There are about 1,500 species in this class (phylum Echinodermata).
Starfish are capable of reproducing both sexually and asexually (regeneration). The main part of these animals are dioecious organisms. Fertilization occurs in water. The body develops through metamorphosis. Some starfish live up to 30 years.
Dartertails (brittle stars)
These animals are very reminiscent of stars: they have thin and long rays. Brittle stars (a type of echinoderm) do not have hepatic appendages, anus, or hindgut. In their lifestyle 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 darter (brittle star) is represented by a flat disk, the diameter of which is up to 10 cm. 5 or 10 thin long segmented rays extend from it. Animals use these bending rays to move, with which they crawl along the seabed. These organisms move in jerks. They extend two pairs of their “arms” forward, and then sharply bend them back. Dartertails feed on detritus or small animals. Brittle stars live on the bottom of the sea, sponges, corals, and sea urchins. There are about 2 thousand species. These animals have been known since the Ordovician.
sea lilies
Echinoderms are very diverse. Examples of crinoids that also belong to 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-swimming and stemless.
Stemless lilies can crawl slowly. They are even able to swim in water. Their diet consists of small animals, plankton, and algae remains. The total number of species is estimated at 6 thousand, of which less than 700 are currently represented. These animals have been known since the Cambrian.
Beautifully colored species of sea lilies live mainly in the seas and oceans of the subtropics. They attach to various underwater objects. It is believed that, however, in the Mesozoic and Paleozoic eras their role in the waters of the seas and oceans was very great.
Sea cucumbers (holothurians)
These organisms are called differently: sea capsules or sea cucumbers. They represent a class of invertebrates such as echinoderms. There are species that humans eat. The common name for edible sea cucumbers is sea cucumber. Sea cucumber is mined on a large scale in the Far East. There are also poisonous sea cucumbers. Various drugs are obtained from them (for example, holothurin).
There are currently about 1,150 species of sea cucumbers. Their representatives are divided into 6 groups. The Silurian period is the time to which the oldest holothurian fossils date.
These organisms differ from other echinoderms in their oblong, spherical or worm-like shape, as well as in the reduction of the dermal 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 their help, sea cucumbers capture food. These animals are bottom-dwelling, although very rarely they are also found living in mud (pelagic). They lead a sedentary lifestyle. Holothurians feed on small plankton or mud.
Sea urchins
These animals live at the bottom or near the bottom. The body of most of them is almost spherical, sometimes ovoid. Its diameter ranges from 2-3 to 30 cm. The outside of the body is covered with rows of spines, calcareous plates or needles. As a rule, the plates are fixedly connected to each other, forming a shell (dense shell). This shell prevents the animal from changing shape. Today there are about 940 species of sea urchins. The greatest number of species was represented in the Paleozoic. There are currently 6 classes, while there are 15 extinct classes.
As for feeding, some sea urchins use dead tissue (detritus) as food, while others scrape algae from rocks. In the latter case, the animal's mouth is equipped with a special chewing apparatus, which is called the Aristotelian lantern. In appearance it resembles a drill. Some species of echinoderms (sea urchins) use it not only to obtain food, but also to modify rocks by drilling holes in them.
The value of sea urchins
These animals are a valuable species of marine biological resources. Commercially it is 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 contained in it can be used for cancer as a therapeutic and prophylactic agent. In addition, they normalize blood pressure, increase potency, and 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 reproductive and thyroid glands, and the cardiovascular system.
Given the above, it is not surprising that the sea urchin is a marine echinoderm that is becoming a coveted dish. For example, residents of Japan eat about 500 tons of caviar from this animal every year, both in its natural form and as additives to dishes. By the way, the consumption of this food product is associated with such a long life expectancy in this country, where people live on average 89 years.
This article presented only the main echinoderms. We hope you remember their names. Agree, these representatives of marine fauna are very beautiful and interesting.
One of the beautiful animals that cannot be found on land is starfish. Divers diving in warm seas often manage to admire these unusual and interesting creatures.
Echinodermata (Echinodermata), which includes starfish, are an independent and very unique type of animal life. In terms of the structure of their body, they are completely different from other animals and, thanks to the peculiarities of their organization and the original shape of their body, they 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 a video that I think is interesting how stars hang out and eat.
They have been known in fossil form since the Lower Paleozoic - from the Ordovician period, i.e. about 400 million years ago. Currently, more than 1,500 modern species of starfish are known, which are systematized into approximately 300 genera and 30 families. Scientists often disagree about the number of orders of starfish. Previously, they were combined into three orders: clearly lamellar, acicular and pedicellariform stars. Currently, they are already divided into 5-9 different groups in various sources. I think that for you and me this is not very important.
Starfish are exclusively marine animals and are not found in fresh water bodies. They also do not live in highly desalinated seas, for example in the Azov or Caspian seas, although sometimes they can be represented by isolated oppressed species. 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 reproduce, and the population of these starfish is supported by larvae carried by currents. And the only starfish that penetrated from the Mediterranean Sea to the Black Sea - Marthasterias glacialis - lives only in its most saline part - in the area of the Bosphorus Strait.
In seas and oceans with normal water salinity, starfish are found everywhere - from the Arctic to the Antarctic and are especially numerous in the warm waters of the seas. The deep habitat range 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 sea stars is more scarce.
The Russian seas are home to about 150 species of starfish, which live, with very rare exceptions, in the northern and Far Eastern seas.
All sea stars as adults lead a bottom-dwelling lifestyle, crawling along the surface of the bottom or burrowing into the ground. Many of the sea stars, especially those living in shallow coastal waters, are active predators, eating various small bottom organisms - mollusks, crustaceans, other invertebrates, including echinoderms, and even fish. They do not disdain carrion.
Among deep-sea starfish, mud-eaters predominate - they use sea soil for food, extracting organic matter from it. Some starfish can eat plankton.
Typically, starfish are not very picky eaters and will eat whatever they can. The diet of, for example, the Chilean sea star Meyenaster includes up to 40 species of echinoderms and mollusks.
Most starfish detect prey and determine its location thanks to substances that the prey releases into the water. Some soft-bottom sea stars, including species of the genera Luidia and Astropecten, are able to find burrowing prey and then dig through the substrate to reach the 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 pedicellariae when the prey stops over or near a starfish.
An interesting way is how sea stars consume many species of bivalve mollusks as food. The star crawls onto the body of such prey and attaches itself to it with its legs on the rays, adding some force towards opening the valves of the mollusk shell. Gradually, the muscles of the mollusk that hold the shell valves closed get tired and open the shell slightly. The starfish turns its stomach inside out and squeezes it into the gap between the valves, starting a meal right inside the shell of the mollusk. Food is digested in this way within a few hours.
The stomach, which turns inside out, is a unique feeding organ for many sea stars. The starfish Patiria miniata from the west coast of America, for example, spreads its stomach along the bottom, digesting organic matter that it encounters.
Starfish usually have a more or less flattened body with a central disk that gradually turns into rays radiating from it. The mouth opening is located on the underside (oral) side of the starfish's disk. Most stars have an anus on the upper part of their body; in some species it is absent altogether. In the middle of the lower side of each ray there is a groove in which there are many soft and movable outgrowths - ambulacral legs, with the help of which the starfish moves along the bottom. A five-rayed structure is typical for sea stars, but there are stars with 6 or more rays. For example, the Heliaster solar starfish has 50 rays.
Sometimes the number of rays varies even among individuals of the same species. Thus, in the sea star 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 greater than the diameter of the disk, while at the same time, in the common Patiria pectinifera star in the Sea of Japan, the rays only protrude slightly beyond the disk, which is why the star has the shape of a regular pentagon . These stars are also called biscuit stars for their resemblance to flat cookies.
There are even sea stars whose appearance is so changed that it is difficult to recognize them as a star. The common inhabitant of coral reefs, New Guinea culcita (Culcita novaeguineae), has a highly swollen body, resembling the shape of a heavily swollen pillow or bun. However, this body shape is only found in adult stars—young culcites have the shape of regular pentagons.
Typically, sea stars that live at shallow depths have a very varied coloration of the upper body. A variety of colors and shades of the spectrum can be present here. Sometimes the colors are spotted and form a bizarre pattern. The ventral side of the body of starfish has a more modest coloration, usually pale yellow.
The color of stars that live 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 colors of starfish depends on the pigment inclusions found in the skin epithelial cells.
The sizes of different types of starfish can vary from a few centimeters to 1 meter. Most often divers encounter starfish measuring 10-15 cm.
The lifespan of some starfish species can be more than 30 years.
The sea star's sensory organs 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, spines, spines, tubercles, etc. But in fact, the skeleton of starfish is not external, like that of mollusks or arthropods, but is located under the skin epithelium, sometimes very thin. The calcareous plates of sea stars do not form a single solid skeleton, but are attached to each other using connective tissue and muscles. Sea stars have a main skeleton, called the supporting skeleton, and various appendages to it - spines, 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 sea stars.
Reproduction of sea stars can take place according to several scenarios. If a ray with part of the disk is torn off from a starfish, then two individuals will be 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, the connective tissue softens and they break up into several parts, usually two. Soon independent starfish will grow from these parts. Species of the genus Linckia sea stars, common in the Pacific Ocean and other areas of the world's oceans, are unique in their ability to cast entire rays. From each such ray, if it is not eaten by a predator, a new starfish can be regenerated. This type of reproduction is called asexual.
Starfish also reproduce sexually. Most star species are dioecious, i.e. represented by males and females. Reproduction is carried out by fertilization of the female's eggs with the reproductive products of the males, which are hatched directly into sea water. A female starfish can lay several million eggs at a time.
Among the stars there are also unisexual (hermaphroid) species. Such species include, for example, the common European starfish Asterina gibbosa, which is a hermaphrodite. Such stars produce both female and male reproductive products in their bodies. They usually carry their young in a special brood pouch or cavities on their back.
The larvae that hatch from the eggs usually feed on plankton and, growing up, sink to the bottom, switching to the usual lifestyle for sea stars
Starfish have no natural enemies. These animals contain toxic substances in their bodies - asteriosaponins, so predators do not deign to pay attention to them. In addition, the body of a starfish is low in nutrients and does not constitute a high-calorie food.
crown of thorns
On the coral reefs of the Pacific and Indian Oceans, a large crown-of-thorns starfish (Acanthaster plansi), reaching a diameter of 50 cm and belonging to the genus Acanthasteridae, is often found.
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 crown of thorns starfish is notorious among the inhabitants of many tropical islands. It is impossible to pick it up without receiving a burning pain from 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, 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 place his foot on its mouth. It is believed that the star sucks out fragments of its needles from the human body, after which the wounds quickly heal.
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 significant increases 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 devoted to the fight against crowns of thorns. The stars were collected in baskets and destroyed, but this did not have a noticeable effect. Fortunately, the outbreaks of crown-of-thorns soon stopped and the coral reefs were not completely destroyed.
Some starfish cause damage by destroying fishing grounds and oyster and mussel plantations. Such pests are collected with special gear from fishing areas and destroyed.
It should also be noted the useful role played by starfish in the ecology of the World Ocean, 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 large number.
In addition, starfish are seabed orderlies, 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 1,600 species of starfish based on the total span of tentacles is considered very fragile Midgardia xandaros. In the summer of 1968, a representative of this species was caught in the southern Gulf of Mexico by the University of Texas research vessel Adaminos. 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 is believed that the five-pointed one has the maximum weight of all starfish. Thromidia catalai, living in the western Pacific Ocean. A representative of this species, caught on September 14, 1969 in the Ilot Amedi area in New Caledonia and later exhibited in the Noumea Aquarium, weighed 6 kg, and the span of its tentacles reached 630 mm
The smallest known was the Asterenid starfish ( 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 most predatory starfish in the world is considered to be the “Crown of Thorns” ( 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 marine aveada can be found is considered to be 7584 m. At this depth, a specimen was discovered by the Soviet research vessel Vityaz around 1962 in the Mariana Trench (western Pacific Ocean). Porcellanaster Ivanovi.
The sea star has small areas at the tip of each star ray that act as light sensors and contain a red pigment that changes color. It is assumed that these areas (flies) influence the movement of the starfish.
The starfish can feed without swallowing food. For example, when encountering a bivalve mollusk, she grabs it and turns its 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 liquefied solution. Spiders also act in a similar way - however, they do not know how to turn their stomachs, but simply inject digestive juice into the victim.
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