How do starfish reproduce? How do starfish reproduce? A starfish is a
What do you know about starfish? Beautiful and unusual creatures, with many interesting facts from their life - in our selection. Currently, about two thousand species of starfish are known.
Starfish do not have a brain or blood - to obtain nutrients, oxygen and other important fluids, the starfish pumps sea water through its body. It is the resulting water that is distributed throughout the body and forms the “water-vascular system.”
On each arm of a starfish, mistaken for tentacles, there are about 15 thousand tiny suckers that help the starfish move.
A starfish is not a fish, but an invertebrate animal.
Starfish are true predators. They are capable of attacking their own kind and can easily feast on the small offspring of their own species, i.e. are cannibals.
Stars have two stomachs, one of which they can even push out to digest shellfish.
Starfish are long-lived, some species live up to 30-35 years.
Many of the starfish are very dangerous. For example, the crown-of-thorns starfish, which is distributed throughout the Indo-Pacific Ocean, is covered in venomous spines. Growing to almost half a meter in length, these creatures become dangerous not only for coral reefs, but also for divers and swimmers.
Starfish can easily change gender and then switch back. True, for such “transformations” several suitable conditions are needed - water quality, temperature and food availability.
Starfish have eyes - exactly as many as there are rays; at the tip of the rays there is an eye, which looks like a red spot. They don’t see very well, of course, but at least they can distinguish between darkness and light.
Even though starfish live underwater, they do not have gills.
Although the appearance of most starfish corresponds to their name, sometimes unusual individuals with bizarre shapes are found. For example, starfish may have a sun-shaped shape, multiple rays, or their shape may be rounded.
The heart of starfish beats at a frequency of 5-7 beats per minute.
The largest starfish can reach 1 meter in diameter and their weight can reach 5 kilograms. Solar stars are more active than their relatives, and are able to rapidly pursue their prey, and, having incredible strength, simply tear apart the shell of mollusks and crustaceans.
The feeding method that allows the starfish to eat prey much larger than the mouth opening is as follows - since the starfish's mouth is on the underside of its body, the star, having grabbed the prey, wraps its strong arms around it, and then with a strong push places it under itself, and then pushes it into the stomach.
They are also some of the most ancient inhabitants of the Earth. Starfish are about 250 million years old.
Stars move using hundreds of tubes that are attached to the surface and then move in waves.
Starfish live at various depths, up to ten kilometers
In the last few years, starfish have begun to actively reproduce. This creates a problem because each individual has an excessive appetite and consumes about 6 square meters of coral per year. In some areas, measures are being taken to destroy stars.
However, starfish still bring much more useful than harmful - they are important consumers of carbon dioxide - every year sea stars collectively destroy about 2% of the Earth's carbon dioxide, and this is an extremely large figure for the entire planet.
Another useful role of starfish is to clean the seabed of carrion, weak and sick creatures of the seabed, as well as the remains of dead oceanic organisms.
Starfish go through five stages of growth before becoming adults - during the first month, stars are free-swimming and jellyfish-like, they are small, almost invisible to the eye and tiny plants and animals of the ocean.
Although most sea stars are not poisonous, a large star called the acanthaster or crown of thorns is dangerous to humans. The pricks of its needles bring burning pain to a person - if the needle gets stuck in the skin, then it breaks off from the star’s body and begins to infect the person’s blood with poisonous secretions.
An interesting fact is that if you cut off one of the arms of a starfish or all of them at once, without damaging the central part of the body, they will gradually grow back.
Starfish are echinoderm invertebrates. The top of the sea star consists of a protective outer frame, below is a mouth and numerous ambulacral legs, which the star uses for movement and feeding. Most stars reproduce sexually, however, asexual reproduction is also quite common.
Let's look at the methods of reproduction in more detail!
Damaged starfish regenerate very easily, rebuilding lost arms and damaged parts of the disk. Species of the genus Asterias can throw off an arm when damaged. Experiments on Asterias vulgaris have shown that regeneration of the entire star can take place if there is one arm and one fifth of the central disk. If the disc fragment includes the madrepore plate, then regeneration will be successful even if less than a fifth of the disc is present. Once the disc and intestines are restored, the animal is able to resume feeding even before the intestines and arm are fully regenerated. Completion of regeneration is slow and sometimes takes as long as a year to complete.
For some sea stars, reproduction by division is a normal form of asexual reproduction. In this case, softening of the connective tissue occurs in the division plane. The most common form of fission is to split the star in half. Each half then regenerates the missing parts of the disc and arms, although extra arms are often created during the process. Species of the genus Linckia sea stars, common in the Pacific and other areas of the world's oceans, are unique in their ability to cast off their entire arms. Each individual arm, unless eaten by a predator, can regenerate a new body. Some species of starfish reproduce clonally during the larval stage. They develop buds on the larval arms, which differentiate into new larvae.
With a few exceptions, starfish are dioecious. Ten gonads, two in each hand, resemble bunches or grapes. In non-reproducing individuals, the gonads are wrinkled and occupy the bases of the arms. However, the gonads of sexually mature specimens fill the arms almost completely. Each gonad releases gametes through its gonopore, usually located between the bases of the arms, although the gonopores of some starfish open sequentially along the arms or on the oral surface. There are several hermaphroditic species. These species include, for example, the common European starfish Asterina gibbosa, which is a protandric hermaphrodite. Most starfish hatch eggs and sperm into sea water, where fertilization occurs. They usually breed once a year and a single female can lay 2.5 million eggs.
Most sea stars have spawned eggs and subsequent stages of development are planktonic. Some starfish, especially cold-water species, brood large, yolk-rich eggs under an arched body, in aboral disc pockets, in gestation baskets formed by spines between the bases of the arms, under the paxillae, or even in the cardiac stomach. In all species that bear eggs, development is direct. Asterina gibbosa is not an egg-bearing species, although it does attach its eggs to rocks and other objects, which is also unusual for this group of animals.
Development
Sea star embryos generally hatch from eggs and begin swimming at the blastula stage. The coelom arises from the terminal part of the developing primitive gut as two lateral sacs that extend posteriorly towards the blastopore (=anus). A small tubular extension of the left coelom (protocoel + mesocoel = axohydrocoel) opens on the dorsal surface as a hydropore, representing a larval nephridiopore. By the time the coelomic cavities and intestines are formed, the cilia larvae in the integument are concentrated within the ciliary cord. It is a curved strip that runs along the surface of the larva, and later rises to outgrowths - the larval arms. Eventually the anterior ventral part of the ciliary cord separates from the rest and forms a separate preoral loop. At this stage, the bilaterally symmetrical larva, feeding on food suspended in the water column, is called bipinnaria.
The ciliary cords serve both for locomotion and nutrition, and the larval arms increase their area. Phytoplankton and other tiny food particles are collected and thrown away from the beat of the cilia, and then transported to the mouth.
Bipinnaria becomes brachiolaria with the appearance of three additional arms at the anterior end. These short arms (brachioles), ventral in location, bear adhesive cells at the ends. Between the bases of the arms is a glandular adhesive disc, or suction cup. Three arms and an adhesive disk are used for attachment when sinking to the bottom. Typically, the brachiolaria is the larval stage that sinks to the bottom and undergoes metamorphosis, but in some sea stars, such as Luidia and Astropecten, settling occurs at the bipinnaria stage.
Metamorphosis
When starfish larvae are ready to settle to the bottom, their positive phototaxis changes to negative. When settling, the brachiolaria is attached with its anterior end to the bottom with the help of brachioles and suckers, which form an attachment stalk.
During metamorphosis, the bilaterally symmetrical larva turns into a pentameric juvenile. In this case, the loss and reconstruction of larval tissues and the morphogenesis of new structures occur and the primordium of the juvenile star is formed at the back on the left side of the body. In this case, the left side of the larval body becomes the oral surface, and the right side becomes the aboral surface. Part of the larval intestine is retained in the juvenile, but the larval mouth and anus are lost and subsequently re-formed in their new positions. The right larval mesocoel degenerates, but the left protomesocoel (axohydrocoel), including the pore canal and hydropore, is preserved and modified in the VSS. The juvenile star's arms are new extensions of the body wall, unrelated to the larval arms. Eventually the young starfish, less than 1 mm in diameter, separates from the larval stalk and crawls away on short arms:
The growth rates and lifespans of sea stars vary greatly, as demonstrated by observations of two species in the intertidal zone of the US Pacific coast. Leptasterias hexactis broods a small number of yolk-rich eggs during the winter, and the young become sexually mature at two years of age, when they weigh about 2 g. The average lifespan of this species is 10 years. Pisaster ochraceus produces large numbers of eggs each spring and development is planktonic. Sexual maturity is reached by the age of five with an animal weight of 70 to 90 g. Individual individuals can live 34 years, reproducing annually.
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 body of the animal 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-building 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 starfish. 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 sea stars, 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!
Class name Asteroidea ( starfish) comes from the body shape of the representatives of echinoderms united in this class, which have the shape of a star, most often five-pointed, or a flat regular pentagon.
Among the animals that have survived to this day, starfish are one of the most ancient groups. In fossil form, they are known from the Lower Paleozoic - from the Ordovician period, which is approximately 400 million years distant from our time.
In seas with normal salinity, various starfish can always be seen close to the shore - in the littoral zone, that is, in an area that is flooded with water at high tide and exposed at low tide. Therefore, starfish were well known to man already in ancient times. Their images were discovered on 4,000-year-old frescoes found during excavations on the island of Crete. The very name Aster, i.e. star, was given to these amazing animals by the ancient Greeks. More than 2 thousand years ago, Aristotle included starfish in the classification of animals he created, and he knew that “when they attack, they suck out many shells.”
Starfish class includes two orders - Platyasterida and Hemizonida, which completely became extinct in the Paleozoic and were studied only from the finds of their skeletal remains, and three orders, numerous representatives of which still exist today:
1) Phanerosonia (from the Greek words phaneros - obvious and zone - belt), or clearly plate-like stars, which got their name from the rows of calcareous plates clearly visible from the outside, bordering the edges of the star;
2) Spinulosa (from Latin spinula - small needle, thorn), or needle stars, and
3) Forcipulata (from the modified Latin forceps - forceps), or pedicellaria stars, i.e. stars that always have numerous skeletal appendages on the surface of the body in the form of tiny pedicellaria forceps sitting on legs.
Despite the general very similar structure of all sea stars, they are very diverse both in external shape, size, color and the nature of calcareous skeletal formations (plates, spines, spines, pedicellaria), on which the appearance of the animal greatly depends, and in their way of life and the conditions in which they live. More than 1,500 living species of starfish are known, belonging to approximately 300 genera and 29 families.
Starfish are typical inhabitants of oceans and seas, the water of which has normal oceanic salinity (about 35°/00). None of the representatives of sea stars managed to adapt to life in fresh waters. In highly desalinated seas, stars are either absent, as, for example, in the Azov and Caspian Seas, or only a few species penetrate into them, represented in these conditions by clearly depressed forms. For example, adult individuals of the star Asterias rubens penetrate into the western part of the Baltic Sea to areas with a salinity of 8°/00 (Near the island of Rügen), but, apparently, are not able to reproduce with such strong desalination, and the population of this star is maintained here for due to the bringing of larvae ready for settling from more saline areas. And the only star that penetrated from the Mediterranean Sea to the Black Sea (Marthasterias glacialis) lives only in its most saline southwestern corner near the Bosphorus Strait and was unable to spread throughout the rest of the sea. This salt-loving nature of sea stars is due to the fact that they all belong to poikilosmotic animals, i.e., those that are not able to regulate the total concentration of salts in the liquids filling the body cavity. Therefore, the concentration of salts in the cavity fluids that wash all the tissues and internal organs of stars depends entirely on the salinity of the surrounding water, and strong desalination turns out to be destructive for these typically marine animals.
Under favorable conditions, some species of starfish can reproduce in very large numbers and form populations of high density. In the oceans and salty seas, starfish are ubiquitous, from the Arctic Ocean and the waters washing the coast of Antarctica to the tropical and equatorial zones of the ocean. They are abundant both in the littoral zone of our northern seas, where they can withstand sharp seasonal temperature fluctuations, and in winter they can even freeze, and in constantly warmed tropical shallow waters, where numerous species live among lush thickets of reef-forming corals. As the depth increases, the diversity of sea stars decreases greatly, but even on the bottom of the ocean floor with its constantly homogeneous conditions - the complete absence of light, low temperature and enormous pressure - they are found everywhere, and representatives of three families (Porcellanasteridae, Pterasteridae and Brisingidae), one at a time from each detachment, penetrate to depths of more than 6 km. During the work of the Soviet expedition vessel "Vityaz" in the Pacific Ocean, two species of stars from the genera Porcellanaster and Hymenaster were found in the northern part of the Mariana deep-sea trench at a depth of 7600 m, which apparently constitutes the limit of penetration of starfish into the depths of the ocean.
All sea stars as adults lead a bottom-dwelling lifestyle, crawling along the surface of the bottom or burying themselves in sand or silt. Many stars, especially those living in shallow waters, are active predators, feeding on various mollusks, crustaceans, coelenterates and other invertebrates, including echinoderms. Along with this, mud-eating forms are also very common among deep-sea stars, swallowing the soil in which they live and using the organic remains contained in it as food.
Apparently, starfish were very numerous in the seas of past geological eras, but complete, well-preserved specimens are quite rare in fossil form. The calcareous plates of sea stars do not form a single strong skeleton, but are held together by connective tissue and muscles. Therefore, more often only scattered plates or imprints of stars are found in fossils.
The most ancient and primitive stars from the Somasteroidea group were described in 1951 by W. Spencer from the Lower Ordovician deposits of southern France. And several years ago, New Zealand zoologist B. Fell assigned the modern star Platasterias latiradiata, which lives in the shallow waters of the Pacific coast of America near Southern Mexico and Nicaragua, to the same group. Spencer and Fell view the group Somasteroidea as subclass of the class Stellate echinoderms(Stelleroidea), to which they include true starfish and brittle stars as the other two subclasses. However, here we consider sea stars and brittle stars as separate classes, according to the classification generally accepted in modern manuals.
Starfish usually have a more or less flattened body with a central disk, gradually turning into rays, or arms, radiating from it (Fig. 138). The downward side of the star with the mouth opening in the center is called oral, i.e. oral, and the upper side is called aboral. Sometimes the oral side is conventionally called the ventral side, and the aboral side is called the dorsal side. In stars that have an anus, it is located near the center of the aboral side of the disk. In the middle of the lower side of each ray there is a groove in which there are numerous soft movable outgrowths - ambulacral legs that serve the star for movement.
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A five-rayed structure is typical for sea stars, but quite a few species have six or more arms. In stars of the genus Labidiaster that live in Antarctic waters, the number of rays can reach 45, and in the solar star Heliaster even 50. Sometimes the number of rays varies among different individuals of the same species. Thus, for the star Crossaster papposus, which is common in our northern and Far Eastern seas, the number of rays ranges from 8 to 16. In some cases, the number of rays for stars of the same species may vary depending on the habitat, in others it may increase as the star grows . The ratio of the sizes of the rays and the disk also varies greatly. To characterize the body shape of starfish, they usually use the ratio of the length of the radius (R), i.e., the distance from the center of the disk to the end of one of the rays, and the interradius (r) - the distance from the center of the disk to its edge in the interval between the rays. Most often, the length of the rays is 3-5 times the radius of the disk. In the most long-rayed stars, for example, in some deep-sea Brisingidae with a very small disk and numerous very thin and fragile rays, R can be 20-30 times greater than r, and in many stars from the order Phanerozonia and in some Spinulosa the rays can protrude only slightly beyond the edges a wide disk and the body has the shape of a regular pentagon, in some cases so flattened that the star looks like a flat cookie, in others more or less convex. There are even stars whose appearance is so changed that at first glance it is difficult to recognize them as starfish. In the common inhabitant of coral reefs, Culcita (Table 19), the strongly swollen body resembles an almost round pillow or bun in shape. However, this body shape has developed secondarily and is characteristic only of adult individuals, and very young culcites look like ordinary pentagonal stars. The recently described species Podosphaeraster polyplax is even more modified (Fig. 139). The only specimen of this unusual starfish was found at a depth of about 80 m in the South China Sea. Podosferaster looks like a ball with a diameter of a little more than a centimeter and looks more like a sea urchin than a star. However, its five ambulacral grooves run only along the lower hemisphere, corresponding to the oral side of other stars, while in sea urchins the stripes of plates with ambulacral legs extend to the upper half of the body. The closest relatives of this star, which together form the family Sphaerasteridae, are known only in fossil form from deposits of the Jurassic and Cretaceous periods. The sizes of starfish vary greatly. In the smallest species, the diameter, or, more precisely, the greatest distance between the ends of oppositely directed rays, does not exceed 1-1.5 cm, while in the largest individuals of some species - Acanthaster and Pycnopodia (Tables 19 and 25) - it can reach 50 and even 80 cm, and Brisingids(Freyella remex) the length of each of its ten arms is 45 cm.
In many stars, mainly in species that live in the littoral zone and at shallow depths, the upper side of the body is often painted in very bright colors, while the lower side usually has a pale yellowish color. The color of the aboral side is dominated by various shades of orange, pink and red, but there are also stars colored violet, blue, green, brown and even black. Sometimes the coloring is spotty and various bright colors can form a bizarre pattern. The stars that inhabit the depths of the ocean are sometimes reddish in color, but more often lack bright pigmentation and appear yellowish or dirty gray. The color of the stars depends on the pigment inclusions located in the skin epithelial cells.
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 - needle plates, small spines, tubercles, etc. However, in reality, the skeleton of sea stars is not external in origin, as, for example, in mollusks or arthropods, but the internal one, formed in the connective tissue layer of the body wall. All parts of the skeleton visible from the outside are covered with integumentary epithelium and a thin layer of connective tissue, but in adult animals these covers on the most prominent parts can be worn away, exposing the skeletal base.
The main supporting skeleton of stars (Fig. 140) consists of numerous individual calcareous plates interconnected by connective tissue and muscles. The skeleton of the oral side is more developed. Along the entire lower side of each ray there are two rows of ambulacral plates, which look like oblong bars lying across the ray. The obliquely located opposite plates of each row are connected by their upper ends, forming, as it were, the roof of the ambulacral groove running along the ray. Adjacent to these plates on each side of the furrow is a longitudinal row of adambulacral plates, followed by two rows of marginal (magistral) plates forming the lateral edges of the rays and disc. In some stars, the marginal plates are large and clearly visible from the outside (Phanerozonia); in others, they are poorly developed and differ little from the skeletal plates on the upper side of the star. Most stars have additional rows of plates to one degree or another, especially in the interradial spaces of the lower side of the disk. The skeleton of the upper body of different stars is developed to very different degrees. Most often, it forms an irregular network of numerous plates touching at their ends (Fig. 141, B).
In one of the interradii of the upper side of the disk, usually near its edge, there is a special madrepore plate, the grooved surface of which is penetrated by small pores. Through the madrepore plate, the ambulacral system communicates with the external environment.
In addition to the supporting skeleton, starfish have various and numerous skeletal appendages, most often in the form of spines or spines, which have a protective value. Usually they are movably articulated with the plates of the main skeleton. The spines can be simple or in the form of paxillae, which are calcareous columns crowned at the top with a group of small spines or needles (Fig. 142, 1-4). In some stars, the paxillae sit on the dorsal surface like this closely that their spines form a continuous cover. Some of the needles are modified into various forms of small forceps - pedicellaria (Fig. 141, L and 142, 5-4), sitting directly on the plates of the main skeleton or on the needles or rising above them on flexible stalks. Mobile and very numerous pedicellariae cleanse the surface of the body from contamination, capturing and discarding foreign particles that fall on it. Along with this, they can also perform a protective function.
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In the spaces between the skeletal plates of the dorsal side, and in some stars also on the oral side, numerous delicate thin-walled outgrowths protrude out into which the body cavity extends - papules, or skin gills, which serve mainly for respiration (Fig. 141, A). To a large extent, breathing occurs through the walls of the ambulacral legs, and sometimes through other areas of the body surface. The stars move with the help of numerous ambulacral legs, extending in pairs from the radial canals of the ambulacral system stretching to the end of each ray (Fig. 123). Through the spaces between the ambulacral plates of the skeleton, the legs extend out into the ambulacral groove. The legs are mostly arranged in two, and in some stars four rows along the entire length of the beam. Their total number in each ray can reach several hundred. Each leg is connected to an ampoule located inside the beam - a muscular sac in the form of a small bubble that can contract and stretch. The legs themselves can also stretch and compress greatly, as well as bend in any direction. Most stars have legs equipped with suction cups at the end. One leg attached to any surface, contracting, can develop a force of up to 30 g, and with the joint coordinated action of numerous legs of several rays, the thrust force developed by the star can reach several kilograms. This, it turns out, is more than enough even to move the star up a vertical plane, as well as to hold fairly large prey and to open tightly closed shells of bivalve mollusks. It is curious that the adhesion force of the sucker stalk to the substrate exceeds atmospheric pressure and more than 40% of this force is due not to the suction effect of the vacuum generated by the sucker, but to the sticky mucus constantly secreted by the glandular cells of the sucker epithelium. The ambulacral legs are equipped only with longitudinal muscles that ensure their contraction, and their stretching is caused by the hydrostatic pressure of the fluid pumped into the legs from the compressed ampoules.
The muscles of starfish are relatively poorly developed. A muscular cord running along the dorsal side of each ray serves to bend the ray upward. The system of muscles connecting the skeletal plates of the oral side ensures the narrowing and widening of the ambulacral groove and the lateral bending of the rays. External skeletal appendages, ambulacral legs, and skin gills are supplied with muscle fibers. The stars of the deep-sea family Benthopectinidae (Phanerozonia), which are characterized by long and flexible rays, are distinguished from all other stars by paired muscular cords running along the sides of each ray along its dorsal surface. Apparently, stars of this family are capable, with the help of such muscles, of making movements that allow them to float up and swim short distances near the bottom.
Although most stars are active predators, they do not have any adaptations for tearing apart prey or chewing food. The specialized oral plates of the skeleton are adapted only for pushing food into the mouth. Surrounded by a soft, leathery space called the peristome, the mouth is capable of stretching widely. It is connected by a short esophagus to the voluminous stomach, which fills most of the internal space of the disc. A short and narrow hindgut extending from the upper part of the stomach opens on the dorsal side near the center of the disc with the anus. However, the latter is so small that it practically cannot serve to remove undigested food residues, and they are thrown out through the mouth. In the upper part of the stomach, paired branched blind outgrowths, the so-called pyloric, or hepatic, appendages extend from it into each ray, into the internal channels of which digestive juices are abundantly secreted. In the walls of the liver appendages, digested food is absorbed and reserves of nutrients accumulate, which can be consumed in cases where the star does not feed for a long time, for example, during the period before breeding or when gestating young. Fasting for 6-8 weeks leads to the complete consumption of such reserves.
In some stars, the hindgut, anus and radial outgrowths of the stomach are absent and the entire digestive tract consists only of a sac-like stomach. Such stars usually belong to mud-eating forms.
Many stars with long and flexible arms, mainly from the Asteriidae family, are able to turn their stomach (its lower part) outward, envelop their prey with it and digest it without swallowing it. No food remains are ever found in the stomachs of such stars. Other stars with short or insufficiently flexible arms are not able to hold prey for a long time. They swallow whole, sometimes quite large animals, and after digesting their soft parts, they throw undigested remains out through the mouth, such as mollusk shells or sea urchin shells.
The food spectrum of many large predatory stars is very wide. Although they usually prefer to feed on one or another specific species of animal, they often eat many others or their carcasses. But some stars have strictly selective nutrition. Some of them eat only sponges, others feed on coral polyps, and the food of Coscinasterias calamaria consists mainly of brachiopods, the shells of which this star opens in the same way as other stars open bivalves.
The nervous system of starfish is very primitive. They do not have any clearly defined cerebral ganglia.
Despite the primitiveness of the nervous system of sea stars, experiments conducted by a number of researchers have shown that some stars can develop conditioned reflexes. In the star Asterias rubens, which is common in the littoral zone of Murmansk, by repeated combinations of food with a certain surface of the substrate on which the star crawls, it was possible to develop a selective reaction to this type of surface. Stars of the same type, entangled in a network, gradually “learned” to free themselves from it much faster than during the first experiments. The conditioned reflexes developed in stars can last up to five days without reinforcement.
Of the morphologically distinct sensory organs, only the eyes are developed in stars. The last unpaired ambulacral leg of each ray lacks a sucker and is a short tentacle, at the base of which there is a red ocellus, consisting of numerous individual eye cups. With the help of its eyes, a star cannot “see” in the proper sense of the word, but is only able to distinguish between the intensity of illumination and the direction of light.
In addition to the unpaired terminal tentacle, several adjacent ambulacral legs also do not have suckers and perform the function of touch. The crawling star always pulls them forward and probes the surface of the substrate with them. In the epidermis of the body wall of stars, sensitive nerve cells are found everywhere. They are especially numerous in the suckers of the ambulacral pedicles, at the bases of the spines and pedicellaria, and on the sides of the ambulacral grooves. In such areas their number can reach 70 thousand on an area of 1 mm2. Apparently, not only the terminal tentacles, but also the suckers of the remaining legs can act as organs of touch. In addition, clusters of nerve cells are able to perceive taste and other chemical stimuli. Stars of some species react to food that is located at a distance of up to half a meter from them. There is even a case described when the star Asterias vulgaris moved directly towards food for two days, which was located at a distance of 12 m from it. Fishermen who set traps for large sea lobsters, lobsters, are well aware that stars often crawl towards the traps and accumulate in them , eating bait intended for lobster. However, sometimes there is virtually no chemoreception. In a number of cases, hungry stars crawled a few centimeters from their favorite food without noticing it, and ate the food only when they accidentally came across it.
Stars do not have special excretory organs. The removal of metabolic end products from the body is carried out mainly by motile amoeboid cells, numerous in the fluid filling the body cavity. Loaded with metabolic products, amoeboid cells move to the surface of the body and exit mainly through thin-walled skin gills. In addition, the end products of metabolism are secreted by special secretory cells into the canals of the hepatic appendages, from where they enter the stomach and are removed outward.
Most starfish are dioecious. But there are also frequent cases of hermaphroditism in its various manifestations. So, for example, in Marthasterias glacialis, along with individuals of one or the other sex, there are also stars with mosaic hermaphroditic gonads. And in Asterina gibbosa, common on the Atlantic coasts of Europe, the so-called proterandric hermaphroditism prevails in populations of some areas, when young stars function only as males, and those grown to a certain size - only as females. But in other areas, stars of the same species may be male, female or hermaphrodite, regardless of size.
In typical cases, in each ray, near its base, there are paired gonads, the ducts of which open outward between the rays or sometimes on the oral side of the body. But in a number of species, numerous gonads are located serially inside the rays and each open outward with its own opening.
In appearance, male and female individuals are usually indistinguishable, except in cases where females take care of the offspring and carry developing young. But sometimes stars of different sexes may differ slightly in size or color during the breeding season. In the already mentioned Asterina gibbosa, during the breeding season, males accumulate around the female and press their rays to her rays in such a way that the released sperm falls directly on the eggs swept into the water. And shallow-water tropical Archaster even unite in pairs when breeding.
The embryonic development of stars can proceed with the stage of a free-swimming larva, from which a young star is formed as a result of metamorphosis, or it can be direct. In most stars, reproductive cells are released directly into the water, where fertilization of the eggs occurs and their further development into a bilaterally symmetrical bipinnaria larva (Fig. 143, L-E). This symmetry of the larva is a trace of the origin of starfish from the distant ancestors of all modern echinoderms, which also had bilateral rather than radial symmetry. After several weeks of life in the water column, during which the larva actively feeds on microscopic algae, three outgrowths are formed at the anterior end of the bipinnaria and it turns into the larva of the next stage - brachiolaria (Fig. 143, F-G). The brachiolaria soon settles to the bottom, is attached by a sucker located between the outgrowths of the anterior end and undergoes metamorphosis, during which the anterior part of the brachiolaria, which acts as a stalk, degenerates, and a young star is formed from the rear part containing the stomach.
With direct development, relatively few large and yolk-rich eggs develop without a free-swimming larval stage. Many stars with this type of development show concern for their offspring to one degree or another. In Asterina gibbosa and some other stars, this care is limited to the fact that they attach eggs to various underwater objects, most often to the lower surface of stones hanging above the bottom, and then crawl away. However, in most inhabitants of the cold waters of the polar regions or great depths, developing embryos and even already formed young stars are borne on the mother’s body until they become capable of leading an independent existence. In particular, all stars inhabiting the Antarctic region bear their young, regardless of which order they belong to.
In stars from the orders Spinulosa and Forcipulata with more or less long and flexible rays, gestation of the young most often occurs as follows. The mother rests on the bottom with the ends of the rays, and bends their bases and disk so that they form something like a bell, inside of which there is a mouth. The developing stars are placed in the cavity of this bell, connected by a common cord, to which each of them is attached with its oral part. During the entire period of bearing her offspring, the mother does not feed. In the small star Leptasterias groenlandica living in the cold waters of the Arctic, the juveniles develop inside the mother's stomach - in special marsupial outgrowths of its front part.
Stars with short wide rays and a less flexible body are not able to form a brood chamber under the oral part of the disk, and the development of juveniles can occur on the dorsal side of the body, or directly on its surface between the paxillae (some representatives of Phanerozonia), or in a special brood chamber ( family Pterasteridae from Spinulosa). A more detailed description of such stars will be given below.
The fertility of stars whose development occurs in the water column can be exceptionally high. According to the calculations of the English researcher J. Gemmill, Asterias rubens released about 2.5 million eggs into the water in just two hours, and during the breeding season, egg laying in this species can occur several times. The well-known expert on echinoderms, the Dane T. Mortensen, found that another star is even more prolific - Luidia ciliaris, whose ovaries can contain up to 200 million eggs. The fertility of stars bearing their offspring is incomparably less. In stars that bear young on the underside of the body near the mouth, developing embryos usually number no more than 200, although sometimes their number can reach up to 1000. And the number of young stars developing on the back or in special brood chambers does not exceed several dozen.
In some stars, along with sexual reproduction, asexual reproduction can also occur by dividing the disk into two parts. The division line usually runs in a certain direction through the interradii, so that the rays of each division resulting from the division remain intact. Both parts of the star begin to exist independently, and their missing rays and sections of the disk are restored. This type of division is found in a number of species of the family Asteriidae (Forcipulata), usually in those that have more than five rays, as well as in some representatives of the family Asterinidae from the order Spinulosa, for example, in stars from the genus Nepanthia common in the tropical waters of Australia (Fig. 144, B). In some species, only young stars can reproduce by division; in others, the ability to divide remains throughout life. Stars that reproduce in this way can rarely be found with rays of the same length: the regrowing rays of one of the halves of the body are much smaller than the rays of the other half, inherited by the star from the maternal individual. In all species of the genus Linckia (Phanerozonia), asexual reproduction occurs in a different way (Fig. 144, A), which we will describe when describing these stars.
Associated with the ability to reproduce by fission is the very developed ability of stars to regenerate, that is, to restore parts of the body lost due to injury. Some stars can restore all the missing parts even after cutting them into several pieces, but usually only in cases where such a piece consists of at least one ray and an adjacent section of the disk. And with Linckia, the entire star can grow again even from part of the beam. There are cases when stars can, when in danger, spontaneously cast off rays and then regrow them. If the end of the beam turns out to be split in the longitudinal direction as a result of injury, then each part can continue to grow independently and a kind of beam is formed, forked at the end in the form of a fork. Interestingly, a star that has lost its entire arm regenerates at a faster rate than when only the tip of the beam is lost. In young stars, lost parts are usually restored faster than in old ones, and in warm-water tropical species faster than in inhabitants of cold-water regions.
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 sea star 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 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 notice the numerous elements of the calcareous skeleton located on the surface of the body - plates, needles, spines, tubercles, etc. But in fact, the skeleton of starfish is not external, like 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.