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 1500 are known modern species starfish, 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 divided into 5-9 different units 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 Baltic Sea(near the island of Rügen), but they do not reproduce here, 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 warm waters seas. The deep habitat range of sea stars is also wide - from surface layers sea, to kilometer depths, although, of course, at great depths species diversity and number of starfish are poorer.
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 sea stars Soft-bottom dwellers, including species of the genera Luidia and Astropecten, are able to find burrowing prey and then excavate 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 starfish known to have appearance so altered 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 living at great depths is also paler - usually dirty gray or with shades gray colors. 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 with the help of 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 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 or acanthaster starfish (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 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 over with a stick crown of thorns belly up and place your foot on his 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. IN different years There have been outbreaks of significant increases in the numbers 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 abundant 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 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 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 Weight Limit Of all the starfish, it has a five-pointed one 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 a depth of 7584 m. At this depth, the Soviet research vessel Vityaz approximately 1962 in the Mariana Trench ( West Side Pacific Ocean) a specimen was discovered 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.
Star-shaped or pentagonal echinoderms. The size ranges from 2 cm to 1 m, although most are 12-25 cm. Many species are brightly colored.
These are sedentary animals with from 5 to 50 rays.
The starfish has 5 (rarely up to 40) rays or arms extending from the central flat or slightly convex disk. As the rays shorten, the body shape approaches a pentagonal one. The hands contain the digestive outgrowths of the stomach and the processes of the genital organs; inside the arms is located along the longitudinal row of vertebrae. The skin is equipped with regularly located skeletal plates, which are armed with spines, spines, and sometimes pedicellariae. The ambulacral legs sit in open grooves that extend along the underside of the rays to the mouth. The legs are flexible tubular projections, usually with suction cups at the end, and are driven by water pressure in the internal channels and ampullae of the ambulacral system. Mouth in the center of the ventral side, anus on the dorsal side; madrepore plate on the dorsal side.
The digestive system is unique. Above the mouth, inside the disc, there are two gastric pouches; ten digestive (liver) outgrowths extend from the upper (pyloric), two in each arm. The lower stomach is capable of everting, enveloping and partially digesting food.
Sense organs: red eye spots at the ends of the rays and tactile endings of the skin.
Sea stars have a highly developed ability to regenerate: restore severed rays. In addition, the part of the starfish, which includes enough large piece central disk, is capable of growing into a full-fledged animal. This genus is especially noteworthy Linckia, in whose representatives the detached ray is capable of developing into a new organism.
The lifespan of a starfish is up to 35 years.
Lifestyle and nutrition
Benthic animals that crawl using ambulacral legs, usually equipped with suction cups. They live everywhere in oceans and seas (except in desalinated areas) to a depth of 8.5 km.
Most sea stars are predators, feeding mainly on molluscs, barnacles, polychaete worms and other invertebrates. Some feed on plankton and detritus; there are species capable of catching prey using pedicellariae.
Reproduction and development
Starfish are predominantly dioecious. Starfish usually have two gonads in each ray, which open at the base of the ray during sexual intercourse. They reproduce by releasing eggs and sperm into the water. After fertilization, a free-swimming larva (bipinnaria, brachiolaria) is formed, which usually attaches near an adult of the same species and undergoes metamorphosis under the influence of its pheromones. Some species - hermaphrodites - carry their young in a special brood pouch or cavity.
Gallery
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Synonyms:- Russia-US maritime border
- Naval and Colonial League
See what “Starfish” is in other dictionaries:
Starfish- (Sochi, Russia) Hotel category: 3 star hotel Address: Volzhskaya street 23, Sochi, Russia ... Hotel catalog
Starfish- asteria Dictionary of Russian synonyms. starfish noun, number of synonyms: 6 acanthaster (2) ... Synonym dictionary
Starfish- Special Marine invertebrate animal of the echinoderm type. Starfish of all colors, sizes, patterns, sometimes regular five-rayed, sometimes multi-rayed, slowly crawl along the bottom (N. Tarasov. The sea lives). The sea itself was teeming with lush life: glowing... ... Phrasebook Russian literary language
Starfish- A marine invertebrate animal shaped like a five-pointed (sometimes more) star... Dictionary of many expressions
Starfish (film)- Starfish L Étoile de mer ... Wikipedia
Crown of thorns (starfish)- This term has other meanings, see Crown of Thorns (meanings). Crown of thorns ... Wikipedia
STAR- female one of the luminous (self-luminous) celestial bodies visible on a cloudless night. So it started to star, and the stars appeared. | Similarity celestial star, a radiant image, written or made of something. Five, six, arched or coal star. |… … Dictionary Dahl
star- stars, plural stars, stars and (obsolete) stars, stars, women. 1. A celestial body, glowing with its own light, appearing to the human eye as a luminous point in the firmament. Star of the sixth magnitude (astron.). A sky dotted with stars. "Transparent... Ushakov's Explanatory Dictionary
Star- y, wine. y; pl. stars, stars, stars; and. 1. Self-luminous heavenly body, similar in nature to the Sun and visible in the night sky as a bright point. Polar z. Cluster of stars. The shining of the stars. The stars light up, shine, twinkle. The stars of the first,... ... encyclopedic Dictionary
Books
- Starfish and spider. The Unstoppable Power of Leaderless Organizations, Ori Brafman, Rod A. Beckstrom. If you cut off a spider's head, it will die; but if you cut off a tentacle from a starfish, it will grow a new one, and the cut off tentacle can grow into a new starfish. Traditional organizations...
Sea stars- These are very unusual animals that live in the seas and oceans. They are invertebrates, belong to the phylum echinoderms and are very similar to stars, as they have rays diverging into different sides. Most often, the sea star has five rays, but there are species with three, four and six rays. The color of the body is often very bright and varied; on the surface there are special hard plates with needles or spines. The sizes of stars vary greatly and can range from 2 cm to 100 cm, but most stars have a diameter of about 20 cm.
Spreading
Starfish are widely distributed across to the globe. They can be found in all oceans and seas and in all climatic zones, but there are more starfish in warm waters than in cold ones, and they are not found at all in fresh waters.
These animals prefer a bottom lifestyle, often live in shallow water, but can also live at depth, but not deeper than 8.5 km.
Now on earth there are 1.6 thousand species of starfish.
Nutrition
Almost all starfish are predators. They mainly feed on marine invertebrates - worms, mollusks, sponges, barnacles, corals and others. Some deep-sea starfish feed on the mud they find on the bottom.
The digestive system of starfish is quite unique. Their mouth opening is located on the ventral side, and two stomachs extend from it. One stomach has the ability to turn outward and envelop the victim, and the second stomach has ten processes that are located inside the rays of the starfish. This unusual digestive system allows the star to eat prey that is larger than itself.
Lifestyle
Starfish are slow, sedentary animals. They usually crawl lazily along the bottom, lie still, or may climb rocks and corals in search of prey. Their movement speed is very low - 10-30 cm per minute. Stars are considered sedentary animals. As a rule, they move no further than 0.5 km from their usual place of residence.
In their development, stars go through several stages of development. From the eggs that adults throw into the water, larvae are first formed and then they gradually turn into an adult starfish. Some species of starfish carry larvae in special brood pouches on their bodies.
Starfish can live 20 years or more.
- Starfish don't have a brain.
- Instead of eyes, starfish have light-sensitive cells located at the tips of their rays.
- Starfish are capable of regeneration - from a detached ray, a new star can develop.
Brief information about starfish.
A living starfish is a real decoration not only of the ocean floor, but also of the aquarium, however, in order for it to please the eye for many years, you need to know about all the conditions of its maintenance.
Starfish in natural conditions
Many ichthyologists claim that this animal appeared about 450 million years ago. How true this statement is is unknown, but one thing is clear: this predator plays a significant role in the harmony and beauty of the underwater depths. Nowadays, such “decoration” is welcome not only at the bottom of the sea, but also in the sea, where it also looks great against the background of other inhabitants.
Even a novice amateur knows what a starfish looks like, so he is unlikely to confuse it with another inhabitant. True, in order for your pet to live well in an artificially created underwater kingdom, you need to take into account a number of features of its maintenance.
Beginners should first acquire an unpretentious species, since more complex varieties, due to the owner’s lack of maintenance experience, may wither or die. Sometimes, together with “living” stones, a small asterine can get into the home sea, which gets along well with other inhabitants and feeds on the algae fouling on the glass. It is not worth removing it, since it does not cause any harm, but it can create a spectacle when it crawls onto the glass.
Structure of a starfish
Of great interest is the structure of the animal, which belongs to the class
Structure
invertebrates and the phylum echinoderms. It is thanks to its multi-rayed body shape that it got its name. Lives at the bottom of the sea great amount varieties that are characterized not by a multi-rayed, but by a pentagonal and five-rayed body shape.
These invertebrates boast a solid calcareous skeleton, which consists of individual plates movably connected to each other, as well as a well-developed ambulacral system, which is a whole network of channels filled with liquid. Skeletal appendages in the form of spines, tubercles and needles located on the surface serve as a kind of “protection”. To clean the skin, the animal uses special grasping organs called pedicellariae. Predators use them to remove dirt and pieces of algae from their bodies, like tweezers. The mouth is located in the center of the disc, on the lower (ventral) side.
If you look at more than one description of these echinoderms, you will find out that most of them are predators. Such individuals feed on other small invertebrate creatures by attaching their legs to them. In this case, the prey is eaten on the spot, since the invertebrate predator, having attached itself, simply turns out its pouch-like stomach and envelops the prey with it.
Reproduction and compatibility of starfish
Red starfish in an aquarium
Not all mysterious creatures of the ocean depths are able to survive in an artificially created “sea,” but the starfish in the aquarium takes root well. However, it is contraindicated to place animals in a body of water inhabited only, since they are very sensitive to the products of their vital activity. In addition, they will be undesirable neighbors for various invertebrate mollusks.
This is especially true since “five-pointed predators” can simply eat them. In a home pond, they can not only attack an animal, but also bite off its rays, and even eat it.
The reproduction of starfish deserves special attention, since they can do this in several ways. For the most part, these animals are divided into females and males, who, to prolong their genus, spawn eggs and sperm directly into the water.
After their fertilization, free-swimming larvae can be seen in the water column. At first, a cluster of larvae is observed around the adult individual, and under the influence of its pheromones, after a few weeks, the babies undergo metamorphosis and are already attached to the bottom in the form of tiny five-linked organisms.
And hermaphrodite individuals bear larvae either near the mouth or on the back in special cavities. The last method of reproduction is that the adult discards one of the limbs, which quickly regenerates and, as a result, four missing ones grow from one ray. In ancient times, shrimp catchers tried to reduce the population of these predatory invertebrates by tearing them into pieces, but by doing so they only increased their number on the seabed, harming the shrimp even more.
Feeding
As mentioned above, these organisms cannot be placed in the same reservoir with shrimp, sponges and bivalves due to the taste preferences of the former. A novice hobbyist must know what these amazing organisms feed on, because improper feeding will quickly affect their condition.
In a home pond, many species have enough fouling of living stones, artificial driftwood and the walls of a “transparent house”, but you can also give pieces of shellfish and shrimp meat, as well as various food for bottom inhabitants.
Feeding should be done once a day and feed should be used as much as the body can eat in one sitting. Otherwise, food residues will accumulate at the bottom, which will begin to decompose and negatively affect the quality of the water.
Are starfish dangerous for humans?
Despite the fact that many echinoderms look quite menacing, bearing spines and having a “warning” coloration, they are completely safe for humans. They do not bite, shock or attack a person swimming in the sea.
True, there are poisonous species, or rather just one species called the Crown of Thorns (Acanthaster planci). The body of this organism is covered big amount sharp thorns that resemble thorns.
The bases of the needles are equipped with poisonous glands, which cause serious poisoning in humans and other sea inhabitants when pricked. They live on coral reefs, which serve as the main food for “prickly” predators.
As for size, this class is represented by creatures ranging in size from a few millimeters to more than a meter. For example, the largest specimen raised from the bottom of the Gulf of Mexico reaches a length of 1.38 meters from one end to the other. This is a fragile brisingid (Midgardia xandaros).
Variety of species
Such deep inhabitants as look great and get along in the same aquarium with the stars. But you shouldn’t house big ones with them. predatory fish, crustaceans and other echinoderms, which can become enemies for them.
Care is not difficult, since the animals clean themselves, find food on stones and walls of the reservoir, and also move little. The colors of the animals are striking in abundance color range and brightness, so against the background of green algae and gray stones they look almost fantastic. And although the animals lead a bottom-dwelling lifestyle, this does not prevent them from creating a surprisingly spectacular effect in their home pond.
It is not for nothing that red sea starfish are very popular among amateurs, because they are not only beautiful, but also not particularly pretentious. Particularly often bought are varieties such as
(Linkia laevigate), Red Linkia (Linkia multiflora), Red Phromia (Fromia milleperella) and others.
Content Features
You should not get capricious species of echinoderms from the very beginning, since sometimes the slightest mistake can lead not only to illness of the pet, but also to its death. Although these creatures do not have blood, they can also get sick because water passes through their bodies. This means that the state of the “five-pointed” friend may well depend on the state of the water in your system. Therefore, enough time must then pass before introducing these delicate organisms into it to be sure that the quality of the water will be at the proper level. It is also worth remembering that the reservoir should be spacious, despite the fact that not very mobile inhabitants will live there.
Not all home sea lovers know how starfish move, so due to ignorance, you can make a number of mistakes when choosing soil.
Among other things, a beginner needs to know what these organisms eat, because they are not always suitable for these animals. Various deep foods are suitable for their nutrition, but echinoderms do not disdain the meat of shrimp and shellfish, because in nature these invertebrates are their favorite food. It is possible that the animal will gorge itself on fouling alone, so you should not sprinkle a lot of food. She will definitely not remain hungry, but as for water, if she is fed heavily, it will need to be replaced as soon as possible.
In general, keeping echinoderms at home is not particularly difficult, but like any other living organism, it will not tolerate neglect. Therefore, before getting this animal, you need to be sure of your knowledge and desire. Only with proper care will the mysterious inhabitant of the ocean depths delight the eye of its owner and arouse the admiration of other people.
Starfish - animals with unusual shape body, thanks to which they attracted the attention of people back in ancient times. Starfish belong to the phylum Echinodermata, in which they are classified as a separate class, numbering almost 1,600 species. The closest relatives of these invertebrates are brittle stars, or snaketails, which are very similar to them, and more distant relatives are sea cucumbers and sea urchins.
Elegant starfish (Fromia monilis).
The main distinguishing feature of starfish is, of course, their body shape. In general, the body of starfish can be divided into a central part - the disk, and lateral outgrowths, which are usually 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, accordingly, includes part of the central disk and a hand. It would seem that such a similar structure should result in the monotony of these living organisms. But the body shape of starfish is very variable. Firstly, 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 latter type of stars have a very high central disk, so they resemble pillows. Thus, in most species of sea stars, 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 the cushion-shaped ones it tends to zero.
This bright ottoman seabed in fact, the New Guinea culcita starfish (Culcita novaeguineae).
Secondly, starfish differ in surface texture and color. Here the variety simply defies description - smooth, spiky, prickly, rough, velvety, mosaic; monochrome and patterned, bright and faded. The color range of these animals includes almost all colors, but most often there are various shades of red, less often blue, brown, pink, purple, yellow, and black. Pale sea stars usually live in the depths, while shallow-water species are brightly colored.
This is the same New Guinea kulzita, but of a different color.
At first glance, starfish seem primitive, because they do not have any noticeable sensory organs, a brain, and are poorly differentiated internal organs, but this simplicity is deceptive.
The Linkia starfish (Linckia laevigata) is bright blue in color and has sausage-like rays.
First of all, it should be noted that starfish have internal skeleton. They do not have a backbone or individual bones, but have many calcareous plates connected to each other in an openwork system.
Openwork plexuses 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 calcareous spines wears off and they become visible from the outside. It is these spines that give starfish their spiny appearance.
The spines on the surface of the starfish are covered with skin, but some of them are already exposed and have a shiny surface.
In addition, on the upper side of the body in many species, calcareous plates may be visible, fused together or forming a network.
A bizarre pattern formed by the skin and skeletal elements of a starfish.
Finally, the third element influencing appearance starfish are pedicellaria. Pedicellariae are modified needles that look like tiny tweezers. In the life of a starfish they play important role, with their help she cleanses the upper side of the body from debris and sand. All skeletal elements are connected to each other by muscles, so after the death of a starfish, its skeleton crumbles into calcareous plates and not a trace remains of the animal.
The acanthaster starfish, or crown of thorns (Acanthaster ellisii) has spiny and poisonous spines.
The muscular system of starfish is relatively poorly developed. Each ray has a muscle cord that can bend the ray upward, and this, in fact, limits the muscle movements of the stars. But mobility is not limited at all. Starfish can crawl, dig, bend, and swim, but they do not do this with the help of muscles.
Scalloped sea stars (Patiria pectinifera) climb on the seaweed.
These animals have a special body system - ambulacral. Essentially, this system consists of 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 flex and move. The central part of this system is the ambulacral legs - 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 is able to perform miracles. For example, it is able to climb a vertical surface, can stick to the glass of an aquarium for a long time, can rear up, swelling up like an angry cat, or maybe, grabbing hold of two rays, push the valves of a mollusk shell apart. And all this is done by an animal practically devoid of a brain and eyes!
Translucent ambulacral legs are visible on the underside of the beam.
To be fair, it is worth noting that starfish do have some sense organs. These are the eyes located at the ends of each ray. The eyes are very primitive and only distinguish between light and darkness; starfish cannot see objects. Starfish are capable of detecting chemicals (analogous to smell), but they sense them differently. Some species are very sensitive and can crawl to the bait for several days in a row by smell, while 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 covers them from above, and also always try to feel their way with the help of small tentacles at the end of each ray. The sense of touch tells the starfish whether it has encountered a victim or a predator. The starfish's brain is replaced by a group of loosely interconnected cells. It is surprising that despite such a primitive structure of the nervous system, starfish can produce elementary conditioned reflexes. For example, individuals who were often caught in nets began to get out of them faster than those who were caught for the first time.
At the end of the ray of the asterodiscus starfish (Asterodiscus truncatus) a formed eye is visible. The beam itself is covered with relief limestone plates.
Another strong, literally and figuratively, system of starfish is the digestive system. The mouth of these animals is located in the center of the disc on the underside of the body, and the tiny anus is located on the back. By the way, starfish rarely use it (in some species it even becomes overgrown), preferring to remove undigested food residues through the mouth. The stomach of these invertebrates has outgrowths extending into rays; reserves of nutrients are deposited in them in case of famine. And starfish regularly starve because they stop feeding during reproduction. The stomach in many species can turn outward through the mouth opening, and it stretches like rubber, taking any shape. Thanks to its expandable stomach, the starfish can digest prey that is larger than itself. There is a known case when the starfish Luidia swallowed such a large sea urchin that it died, unable to spit out its remains.
A tiny anal opening is visible in the middle of the central disc of Phromia monilis.
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 or lungs, so starfish are sensitive to lack of oxygen. They also cannot tolerate desalination of water, so they are found only in seas and oceans. The sizes of these animals range from 1-1.5 cm for the miniature spherical star Podosferaster to 80-90 cm for the sea star Freyella.
The name of this starfish speaks for itself - fromia elegans.
Starfish 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 waters. Most species prefer to live in shallow waters, some even end up on the shore during low tides. But among these animals there are also deep-sea species, including those that live at depths of over 9 km!
Starfish in shallow water.
Sea stars most time crawling along the bottom. They do this very slowly, the usual speed of a medium-sized individual is 10 cm per minute, but a starfish can “hurry up” at a speed of 25-30 cm per minute. If necessary, these animals climb onto stones, corals, and algae. If a starfish falls on its back, 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 turns its body and takes its usual position. Some species can even swim awkwardly short distances. Starfish can be called sedentary animals; their tagging has shown that they do not move more than 500 m from the place of initial catch.
The coriaster starfish (Coriaster granulatus) looks like a bun.
Despite their outward primitiveness and apparent helplessness, starfish are formidable predators. They are quite voracious and never refuse prey, with the exception of the period of gestation. Only deep-sea species feed on silt, from which they extract food particles; kulcite sea stars, which prefer to eat fouling on corals, can also be called conditionally “non-predatory”. All other species actively hunt other animals.
Not at all romantic relationship connected this pair: the sea star Solaster dawsoni eats the spiny hippasteria spinosa.
Most starfish are picky; they eat everything they can hold with their hands and whatever their “rubber” stomach can reach, not disdaining carrion. Some species can only feed on a certain type of food: sponges, corals, gastropods.
The pretty starfish (Pentagonaster pulchellus), 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 bivalves. The star catches the sea urchin by crawling and eats it with its mouth. Bivalves have shells whose valves close tightly in case of danger, so starfish treat them differently. First, the starfish sticks with two rays to the shell flaps, and then begins to move them apart. It must be said that the ambulacral legs are firmly glued to the substrate thanks to an adhesive lubricant, and one single ambulacral leg can develop a force of up to 30 g! And on each ray of the starfish there are hundreds of them, so she, like a real strongman, pushes the shells apart with an effort of several kilograms. However, the starfish does not need to spread the shell flaps to their full width; for a hearty lunch, a gap of 0.1 mm is enough for it! The starfish turns its stomach into this truly microscopic gap (it can stretch up to 10 cm) and digests the mollusk in its own home.
Asteria starfish (Asterias rubens) reaches out to a clam.
Most starfish are dioecious; very few species have both male and female gonads. The gonads are located in pairs at the base of each ray. In the asterine starfish, the young are first male and then change to female. A special exception is the ophidiaster starfish, which has no males at all! Females of this species lay eggs without fertilization, a process called parthenogenesis. During mating, males and females connect their rays and release 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 200 million in species with free-swimming larvae.
Mating starfish.
Starfish larvae come in three types. In some species, the eggs hatch into a free-swimming larva, 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 large reserves of yolk, so it does not feed and immediately turns 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. During this period, a caring female rests only on the tips of the rays, and arches her body into a dome, under which the offspring 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 the life cycle of sea stars; it is during this period that the young can be carried by currents over very long distances.
The starfish larva has bilateral symmetry.
In addition to sexual reproduction, starfish can also reproduce asexually. Most often this occurs in multi-rayed 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 following traumatic injury to the body. If a starfish is artificially divided into several parts, then a new organism will be formed from each. Even one beam is enough for restoration, but a piece of the central disk is required. Starfish grow slowly, so they look lopsided for many months.
A new individual is formed from the cut off ray of a starfish. This shape is often called a comet.
IN natural environment starfish have very few enemies, since the sharp spines, which can be poisonous, scare away large predators. In addition, these invertebrates, on occasion, try to bury themselves in the sand so as not to attract attention. Most often, sea stars fall into the teeth of sea otters and seagulls.
A seagull caught a starfish.
But the starfish Astropectens is friends with polychaete worms. One individual can have up to five cohabitants, who prefer to stay on the underside of the body close to the star’s mouth. The worms pick up the remains of her prey and even stick their heads into her stomach! The echinaster sea star is inhabited by a special type of ctenophore, which cleans 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 waters, but starfish were of no economic interest to them. Only in China are they sometimes eaten, while attempts to feed starfish to domestic animals can lead to the death of the latter. This is likely due to toxins that some species accumulate by eating coral and poisonous shellfish. But with the development of the maritime economy, people began to classify these animals as their enemies. It turned out that starfish often eat bait in bottom traps for crabs, and also raid plantations for breeding oysters and scallops. In a few years (that’s how long it takes to grow oysters), starfish can destroy an entire oyster bank. At one time they tried to destroy the predators by cutting them into pieces, but this only increased their numbers, because from each stump a new starfish grew. Then they learned to extract starfish with special trawls and kill them with boiling water.
A very impressive mosaic starfish (Iconaster longimanus).
The worst pest was the acanthaster starfish, or crown of thorns. This very large echinoderm feeds exclusively on corals; after itself, 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 ate up a huge section of the Bolshoi barrier reef off the coast of Australia. The unique geological formation was under 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 it is not fatal. Specially trained divers collected the acanthasters into bags with sharp spikes or injected a lethal dose of formaldehyde into the body of the starfish. Only in this way was it possible to pacify the invasion of voracious predators and save the reef. Nowadays, all species of starfish are in a safe condition and do not need protection.
The crown of thorns eats the coral.
