Starfish and their relatives are called echinoderms. Many representatives of this group are indeed extremely prickly. These creatures, quite numerous and widespread, live in the sea, and for this reason many of them are not well studied. Unlike most animals, the body of echinoderms has radial symmetry. Another feature of echinoderms: small hydraulic (fluid-filled) legs ending in a suction cup. Most groups of marine animals include several species adapted to life in fresh water or on land. There are none among echinoderms. These creatures are relatively large in size, many are brightly colored, and are usually easy to see because they move slowly.
The body of starfish is flattened and equipped with the semblance of arms, which radiate in rays from the center of the animal’s body.
Usually the number of rays of starfish is 5, but there are species with 7 and even 14 rays. The animal's upper body usually bears small, hard protective plates or spines embedded in the skin. On the underside, each ray is equipped with rows of tiny tube feet, like miniature fingers with suction cups at the ends. The rays are able to bend, allowing starfish to glide easily along the seabed. Sea stars have sufficient strength to open shells. Starfish
presses a pair of rays to each side of the shell. Then, with great strength and no less patience, she begins to unclench the doors. As soon as a small gap appears between them, the starfish immediately pushes its stomach, turned outward through its mouth, into it. From this moment on, the predator begins to digest the flesh of the prey. Soon the shell finally opens and the starfish finishes its meal.
Red starfish (Asterias rubens) very numerous in the White Sea. Sometimes they move slowly along the seabed in huge schools covering an area of 2.5 square km, feeding on bivalves, worms, crabs, and other echinoderms. Stars of the genus Astropectens prefer a sandy seabed, into which they submerge halfway. Five rays of this beautiful star equipped with spikes. The fourteen rays of the fairly common solar starfish are bright red and resemble the rays around the sun's disk. She even hunts other starfish.
Brittle stars, or snaketails, - the fastest and most active among echinoderms. Their "arms" are very flexible, and brittle stars can walk by bending them. Moving on your “hands” is much faster than using hydraulic legs. Most brittle stars live below the tidal zone, in deep water. Sometimes they are found in clusters of up to 1000 individuals on an area of the seabed of several square meters. Most brittle stars feed by collecting small edible food particles in the mud or filtering them from the water. Species living in the Atlantic and Mediterranean regions are filtrate feeders. They live in a dense colony, where each individual strives to grab all edible food particles floating by with its spiky rays.
sea lilies They were once very numerous, but now they are much smaller. Like all echinoderms, they are equipped with feathery arms-rays, which they use for feeding and movement. Many have up to ten rays, but there are species whose number of rays reaches 200! Sea lilies lead a life attached to rocks, but some can also crawl. These animals feed by filtering food particles from the water with their developing rays. The most ancient sea lilies are attached to the bottom with a stalk.
If Starfish damaged or lost part of the “arm”, she is able to regenerate this lost part. The reconstructed limb is usually slightly smaller. Sometimes it splits into two branches, resulting in a starfish with six arms!
Crown of thorns starfish feeding. Sometimes they multiply so much that they completely consume the coral reef. Natural enemies they don't have much: they are covered with sharp, poisonous spines.
The Pacific sea star Linkia moves very slowly, which, however, does not prevent it from being a successful predator.
Starfish don't look like wine, but they all are ferocious predators.
Echinoderms:
- 6250 species
- Marine life
- Five-ray symmetry
- Internal skeleton, spines often protrude outward
- Tiny tube feet
Main classes:
1. Sea stars
- 1500 types
- Usually 5 rays (sometimes more)
2. Brittle stars
- 2000 species
- Flattened and star-shaped
- Usually 5 rays (sometimes 6 or branched rays)
- The rays are long, fragile and flexible
3. sea lilies
- 625 species (mostly stemless)
- There are floating (stemless) and sessile (stalked) forms
- They feed by filtering water
Starfish belong to a species of the echinoderm class. To their closest relatives
include such marine animals as: sea urchins, brittle stars, sea lilies and sea cucumbers. All these inhabitants of the sea arose more than 450 million years ago, before the appearance on Planet Earth of the now extinct ammonites and insects, fish, reptiles, birds, mammals, conifers and ferns, which are still alive today.
There are approximately 1,500 species of starfish in the world.
All echinoderms are marine animals. Adult starfish are able to crawl along the seabed, and their microscopic larvae swim in the water column. The sizes of adult starfish range from 10 mm to 100 cm in diameter.
Starfish living in Primorye
Primorye is home to more than twenty species of sea stars, 25 to be exact, here are some of them: Patiriya crest, Distolasteria japonica (spinous), Letasteria nigra, Asteria Amur, Easteria spiny, Easteria reticulata, Acantaster, Aphelasteria japonica, Porcelanasteride, Solaster pacificis, Lysastrosoma antosticta, liudia bisquila, common Amur star, crossaster, henricia Hayashi and other species of starfish.
One of the most common sea stars in the Primo region is Asteria Amur. Its body consists of five rays and a central disk. Each beam has up to 400 legs. Is it easy to control a five-armed body with many legs? After all, in nature there are fifty-rayed stars. Starfish with help complex system sensory organs (at the tip of each ray there is an eye, a branched nervous system, on the body along the entire surface there are receptor cells that respond to mechanical and chemical stimuli) feels confident and calm in life. seabed, is even a predator, eating mollusks (oysters, mussels) and echinoderms (littorines and scallops).
Characteristics of starfish by variety
The speed of a sea star moving along the bottom is several centimeters per second; it is interesting that the star searches for its mollusk prey by smell. Approaching the prey, the star feels it with its ambulacral legs, which are located at the tips of the rays. After which they cling with two rays to one leaf, and with three rays to the other, then stretch them.
After a long battle, almost many hours of struggle, the mollusk gives up tiredly, at this moment the star turns out its so-called stomach and launches it between the valves. Digests food externally. After some time, the mollusk leaves a clean shell.
Some starfish, for example, Distolasteria japonica, extract bivalves from the top layer of sand. It slowly rotates directly above the mollusk, which has climbed into the sand, and with the help of ambulacral legs transfers grains of sand from the beginning to the tips of the rays. It turns out that the star turns out to be lower and lower over time and, having descended, reaches the mollusk.
Acantaster, aka crown of thorns, is a starfish with impressive spikes on its back, aka “crown of thorns”, feeds on corals and lives in the tropics. She crawls onto a coral colony and eats them in an amazing way, releasing her stomach.
An interesting fact is that among starfish there are also herbivorous inhabitants of the Porcelanasteridae family, living in the tropics and feeding on unicellular algae.
Starfish, like all animals, are dioecious, meaning that they have females and males.
Reproduction of starfish
External fertilization occurs in seawater. Most species of stars develop their young in water, but not all, because some have brood chambers on their dorsal side for bearing young. The larvae reach 3-5 mm in length. Starfish larvae, unlike adults, are bilaterally symmetrical. They have digestive organs - the esophagus, stomach, ciliary cord - an organ for collecting food particles and a hindgut. Star larvae feed on single-celled planktonic organisms
algae.
They exist as larvae for several weeks, then sink to the bottom, attach to it, and after a period of metamorphosis turn into a small five-rayed starfish with a diameter of 0.5 mm. Puberty in starfish it occurs at the age of 2-3 years.
Features of the structure of starfish
A characteristic feature of the structure of the marine animal is that all the rays are structured the same. This suggests that the five-rayed sea star has many organs in 5 copies. On each ray there are 2 outgrowths of the stomach - hepatic outgrowths. The ambulacral canals and radial bundles of nerves run along the entire length of the beam. All organs are united into one system in the center of the star (disk): in the stomach they are united digestive system and opens with the mouth, the nervous system is connected into a nerve ring, the ambulacral system is connected by the ring ambulacral canal.
The ambulacral system, filled with water under weak pressure, produces shoots into each leg (ray). The elasticity of the ambulacral system together with the muscles of the legs ensures musculoskeletal function. The madreoporous plate is located on the dorsal side of the body. Outwardly, it resembles a lime strainer up to 5 mm in size, and plays the role of a filter, located at the entrance to the circulatory and ambulacral systems of the star. Sea water is passed through it, then enters and flows out of the ambulacral system.
The skeleton of a starfish consists of hundreds of oddly shaped calcareous bones, which are located in the skin and connected by muscles. This unusual structure of the skeletal system makes it possible to bend, take bizarre poses and at the same time strengthen the star’s integument.
Thin short outgrowths are visible on the dorsal side of the animal. These are papules - skin gills. Through them, or rather the walls of these villi, the process of gas exchange occurs. Simply put, the starfish breathes through the skin of its back.
These are sedentary animals; the function of dispersal of species is almost always performed by larvae.
Sea Star Habitat
Starfish live only in seas with a salinity of 35% (35 g of sea salt per liter of water). In connection with this, there are none in the Baltic and Caspian Seas, and very few in the Black Sea.
Summer and winter temperature values sea water off the coast of Primorye differ significantly, and these differences are greatest in the littoral zone. IN winter time the surface of the water freezes to -2 ºС, and in summer time warms up to 25ºС or more. Apparently because of this, about ten species of starfish live in the littoral zone of Peter the Great Bay, but only 2-3 species of stars are found.
Most often found off the coast is Patiria comb - a star with short blue rays, with numerous scattered red-orange spots on the dorsal surface. It is found in five-ray, six-ray and seven-ray. In July-August, during spawning, they form numerous clusters on the bottom.
Asteria Amur is just as easy to catch your eye - a five-pointed star of lilac color with many shades. A few years ago, scientists from New Zealand unexpectedly discovered this species of star on their plantations, feasting on artificially grown shellfish. How did she end up there? It's very simple, she penetrated from Sea of Japan to the shores
Tasmania via ships. These ships take seawater as ballast, and along with it they take away the larvae of local marine life. Distolasteria japonica, similar to Asteria Amur, is black and white in color, and the madrepore plate, as well as the tips of its rays, are painted bright yellow. Near the shore, on the rocks, Letasteria black and dark cream is found; the rays have wide transverse stripes.
Also found on rocky bottoms is an active predator that feeds on mussels, Aphelasteria japonica, crimson-colored, with rays that easily break from the base of the disc. The largest star in Primorye is considered to be the one with a ray span ranging from 40 cm to 50 cm or more. It lives at a depth of four to one hundred meters.
The importance of starfish in the balance of the sea
The role of starfish is noticeable if only because of their large numbers. Being predators, they influence the number of their prey - balanus, mollusks, polychaete worms, often eating them in large volumes, and change the composition of the sea bottom fauna. In artificially created mussel plantations, starfish play an important positive role.
They are useful because they thin out, eating some of them, after which the remaining mussels grow larger.
When alive, the starfish is not a food product. Because they, or rather their bodies, contain toxic substances - asteriosaponins. Eventually Marine life bottoms turn out to be practically invulnerable, being consumers (POV - consumers organic matter) 2nd order.
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. It is true that in an artificially created underwater kingdom your pet has a good life, 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 adult, 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 fancier definitely needs to know what these animals eat. amazing organisms, 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 is poisonous species, or rather, one species called 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 Gulf of Mexico, reaches a length from one end to the other of 1.38 meters. This is a fragile brisingid (Midgardia xandaros).
Variety of species
Such deep inhabitants, like, they 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 their abundance of colors and brightness, so against the backdrop 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 when proper care the mysterious inhabitant of the ocean depths will delight the eye of its owner and arouse admiration among other people.
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 Echinodermata, being relatives sea cucumbers, brittle stars, sea lilies, holothurians, 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? - Thanks to characteristic feature the structure of the star - each of its rays is structured identically, 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), located in a groove on on the ventral side of the papules - skin gills in the form of thin short villi, located on the back and producing gas exchange processes of the genital organs (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 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. Main system the starfish, which we deliberately left “for dessert”, is ambulacral. 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 are attached to different subjects 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), stomach, esophagus and hindgut. 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. According to scientists, these brightly colored legendary inhabitants of the seas also make a significant contribution to the recycling process carbon dioxide, produced including by industrial facilities on the planet - their share is about 2% CO2, that is, more than 0.1 gigatons of carbon per year, which, you see, is not at all weak for such seemingly small creatures!
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.
home distinguishing feature starfish is, of course, a body shape. In general, the body of starfish can be divided into central part- 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 colorful ottoman on the seabed is actually the New Guinea 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 an 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.
A young starfish has skeletal elements hidden under 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 catching chemical substances(analogous to smell), only they feel 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, starfish that were often caught in nets began to get out of them faster than those that were caught for the first time.
At the end of the ray of the asterodiscus starfish (Asterodiscus truncatus) a formed eye is visible. The beam itself is covered with relief limestone plates.
Another “strong” system, in the literal and figurative sense of the word, of starfish is the digestive system. The mouth of these animals is located in the center of the disc on the underside, and the tiny anus is located on the dorsal side of the body. By the way, starfish rarely use it (in some species it even becomes overgrown), preferring to remove food debris through the mouth. The stomach of starfish has projections extending into rays; in these projections, reserves of nutrients are deposited 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 size of sea stars ranges 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 - elegant fromia (Fromia elegans).
Starfish have a global distribution. They are found everywhere in all seas and oceans from the tropics to the poles. Of course, in warm waters species diversity higher than in cold ones. 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 they crawl along the bottom, they do it very slowly, the usual speed of an average-sized starfish is 10 cm per minute, but a sea star can “hurry up” at a speed of 25-30 cm per minute. If necessary, starfish can climb onto rocks, 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 are even capable of swimming awkwardly over short distances. Starfish can be called sedentary animals; tagging of animals 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 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.
A completely non-romantic relationship ensued between the sea star Solaster dawsoni and 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. sea urchin the star comes crawling and eats it with its mouth. Bivalves They 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 the star, like a real strongman, pushes the shells apart with a force 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 2-200 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 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, the caring female rests only on the tips of the rays, and arches her body into a dome, under which the larvae are located. Since the larvae are located near the mouth opening, the female does not feed during this period. The larval form is the most mobile in life cycle starfish, it is during this period that the larvae can be carried by currents over very long distances.
The starfish larva 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 damage to the body. If a starfish is artificially divided into several parts, then each will form new organism. 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 seagull caught a starfish.
But the starfish Astropectenus is friends with polychaete worms. One star can have up to five cohabitants who prefer to stay on the lower side of the body close to the star’s mouth. The worms pick up the remains of the star's prey and even... stick their heads into its stomach. Ctenophores live on the echinaster starfish special type, which clean the surface of the star from fouling.
These bright spots on the Luzon starfish (Echinaster luzonicus) are ctenophores (Coeloplana astericola).
Since ancient times, people have paid attention to the colorful animals of shallow waters, but starfish were of no economic interest to them. Only in China are starfish 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 starfish 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 starfish 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 most a malicious pest It turned out to be an acanthaster starfish, or crown of thorns. This very large starfish feeds exclusively on corals, leaving a crown of thorns behind. coral reef just a white lifeless path. At one time, these stars multiplied so much that they literally destroyed a huge section of the Great Barrier Reef off the coast of Australia. The unique geological formation was under 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.
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