Why does a starfish color the water? Where do starfish live?
Starfish are veterans of the seabed, they appeared more than 450 million years ago, ahead of many forms of modern inhabitants of the underwater depths. They belong to the class Echinoderms, being relatives of sea cucumbers, brittle stars, sea lilies, sea cucumbers, sea urchins - currently there are about 1600 species of them, having a star-shaped or pentagonal shape.
The starfish, despite its inactivity and the absence of a head as such, has a well-developed nervous and digestive system. Why, exactly, “echinoderms”? It's all about the hard skin of the starfish - on the outside it is covered with short needles or spines. Conventionally, these bizarre creatures can be divided into three groups: ordinary starfish; feather stars, named for their writhing rays (up to 50!), and “fragile” stars that cast off their rays in case of danger.
True, it will not be difficult for this animal to grow new ones, and new stars will soon appear from each ray. How is this possible? - Due to the characteristic feature of the star’s structure, each of its rays is structured in the same way, and contains: two digestive outgrowths of the stomach, performing the function of the liver, a red eyespot at the tip of the ray, protected by a ring of needles, radial bundles of nerves, olfactory organs (they are also suckers and a method of movement), papules located in a groove on the ventral side - skin gills in the form of thin short villi, processes of the genital organs located on the back and producing gas exchange (usually two gonads on each ray), a skeleton consisting of a longitudinal row of vertebrae inside, and hundreds of calcareous plates with spines, covering the skin and connected by muscles, which not only protects the animal from damage, but also makes its rays very flexible. The bodies of starfish are 80% calcium carbonate.
Thus, each ray of a starfish, once separated from its body, is completely viable and quickly regenerates. Well, connected together, the rays form closed systems in the center of the animal: the digestive system passes into the stomach from two sections and opens with a button-shaped disk, which serves as the mouth; bundles of nerves unite into a nerve ring. The main system of the starfish, which we deliberately left “for dessert,” is the ambulacral system. This is the name given to the water-vascular system, which serves the echinoderm simultaneously for respiration, excretion, touch and movement, together with the muscles providing musculoskeletal function. Canals extend from the perioral ring into each ray, from them, in turn, lateral branches to hundreds of cylindrical tubes on the surface of the body - ambulacral legs containing special ampoules and ending with suction cups. An opening on the back, called the mandreoporous plate, serves to connect this system to the external aquatic environment.
So how does the ambulacral system work? - It is filled with water under slight pressure, which, entering through the mandreoporous plate into the perioral canal, is divided into five ray channels and fills the ampoules at the base of the legs. Their compression, in turn, fills the legs with water and stretches them. In this case, the suckers of the legs attach to various objects of the seabed, and then sharply contract, the ambulacral legs are shortened, and thus the animal’s body moves in smooth jerks.
Starfish are voracious predators, although there are exceptions in the form of herbivorous species that feed on algae and plankton. In general, the favorite delicacies of these animals are clams, mussels, oysters, scallops, littorinas, barnacles, reef-forming corals and various invertebrates. The star finds prey by smell. Having discovered a mollusk, it attaches itself with two rays to one shell valve, and the remaining three to the other valve, and a many-hour struggle begins, which the starfish always wins. When the mollusk gets tired and the doors of its home become pliable, the predator opens them and literally throws its stomach onto the victim, turning it outward! By the way, food digestion occurs outside the animal’s body. Some starfish are even capable of digging out prey hiding in the sand.
As for reproduction, most starfish are divided into males and females. Fertilization occurs in water, after which free-swimming larvae called brachiolaria are formed. Unlike adult individuals, their structure is subject to the laws of symmetry, and includes a ciliary cord necessary for collecting food particles (exclusively unicellular planktonic algae), a stomach, esophagus and hind intestine. Usually the larvae swim near an adult sea star of the same species - and after several weeks, under the influence of its pheromones, they undergo metamorphosis: having fixed themselves on the bottom, they turn into tiny (0.5 mm in diameter), but already five-linked sea stars. But these babies will be able to give birth only after two or three years. If the larvae perform the function of dispersing species, and drift over long distances, they are able to delay their transformation into adults and not settle to the bottom for several months - and they can grow up to nine cm in length. Among the starfish there are also hermaphrodites - they carry their young in a special brood pouch or cavities on their backs.
Taking into account the large number of starfish, it is clear that they also influence the growth of populations of the species that are hunted. Nobody risks hunting them, since their bodies contain extremely toxic substances - asteriosaponins. Being virtually invulnerable, starfish are at the top of the marine food pyramid and can therefore have a lifespan of up to 30 years. If you believe scientists, then these brightly colored legendary inhabitants of the seas also make a significant contribution to the process of recycling carbon dioxide, including those produced by industrial facilities on the planet - their share is about 2% of CO2, that is, more than 0.1 gigatons of carbon per year, which, you see, is not weak at all for such seemingly small creatures!
Most starfish have a rough eye at the tip of each arrow. These compound eyes contain multiple lenses (ommatidia), each of which creates one pixel in the overall image that the creature sees. Tropical starfish are able to see crude images with their own eyes, which allows the animals to stay closer to home.
Scientists have found that some species of deep-sea starfish, found at depths of up to 1 km below the surface of the water, where sunlight does not penetrate, can see despite the darkness. Most species that can see in the dark depths of the ocean have more sensitive eyes, but see grosser images. These same starfish seem to distinguish objects more clearly than their tropical counterparts living on the light shallows.
Scientists offer different explanations for this. Some species seem to see clearly in the horizontal direction, but less clearly in the vertical, which is absolutely true for an organism that lies on the seabed. Other species appear to be less able to detect changes in what they see over time.
These two species are also bioluminescent, meaning they are capable of producing short flashes of light on the surface of their bodies. The combination of these flashes of light and the ability to see clearly allows these deep-sea starfish to communicate with potential mates.
Regeneration
Hungry predators, crabs or fish, can bite off the arrows of starfish. If a fight ensues, some species of starfish voluntarily lose their limbs so that the rest of their body can escape. Moreover, they can regenerate an entire limb. If you find a starfish that has one arrow that is smaller than the others, there is a good chance it is a new limb.
On sea water
Starfish do not have the usual set of muscles. Instead, they move with the help of seawater, which is pressurized in the vascular system of their bodies. They draw seawater through the pores, then it passes through internal channels into the limbs, and these already set thousands of tubular “legs” in motion.
The muscles and valves inside each tube compress the water, allowing them to stretch and retract, creating movements similar to walking with your feet, but multiplied hundreds of times. At the end of each tube foot is a tiny suction cup that can stick to surfaces and help propel stars.
Gastric Ejection
Starfish are extremely efficient seabed predators, feeding on a wide range of foods - mussels, clams, oysters. They sneak up on their prey and use their legs to simultaneously grab the prey and pin it to the sea floor.
If the prey is small enough, the starfish will swallow the entire animal by inflating its stomach, located in the center. While maintaining a death grip position, the starfish will gradually dissolve the edible soft tissue using enzymes inside the stomach and then discard the inedible hard parts of the shell.
But if the prey is too large to fit into its stomach, the starfish will first try to open the shell and then push its stomach into the gap so that it can destroy the soft tissue inside the victim and digest it right in its house, as if sucking it through a straw.
Starfish are amazing!
Structure and physiology
Adult echinoderms are characterized by radial and usually pentaradial body symmetry, while their larvae are bilaterally symmetrical. Thus, echinoderms have secondary acquired radial symmetry bodies. All echinoderms go through a five-ray stage of development, even if they eventually regain bilateral symmetry (sea cucumbers, irregular sea urchins). Many crinoids and some starfish have many arms, usually a multiple of five. Some brittle stars ( Gorgonocephalus arcticus) arms branch, forming a complex tree-like structure.
In adult echinoderm there are oral the side on which the mouth is located, and the opposite aboral the side on which the anus is usually located. The oral side of actively moving sea stars, brittle stars and sea urchins faces the substrate along which the animal crawls. The body of sea cucumbers is elongated in the oral-aboral direction: the mouth is located at one end and the anus at the other. Sea lilies lead a sessile lifestyle, attaching to the substrate with the aboral side.
The rays (arms) of an echinoderm are called radii. On the oral side of each radius there are usually ambulacral legs, with the help of which the animal moves. Opposite the radii are interradii. The external radial symmetry of the animal is disrupted by the madrepore plate, located on one of the interradii.
The sizes of echinoderms vary from a few millimeters to a meter, and in some extinct species - even up to 20 m. The body of starfish and brittle stars has a pentagonal or stellate shape, sea urchins are spherical, heart-shaped (heart-shaped sea urchin Echinocardium cordatum) or disc-shaped (flat sea urchins) shape, in holothurians the body is barrel-shaped or worm-shaped, and in crinoids it resembles a flower.
Covers and skeleton
The color of echinoderms is varied
Echinoderms, unlike all other animals, can reversibly change the rigidity of their integument and connective tissue. They have connective tissue that can change its rigidity - the so-called mutable connective tissue. The extreme values of hardness are as different as ice and water. When a starfish arches over a prey (such as a mollusk), it stiffens its connective tissue and its rays become a support for the ambulacral legs, which are attached to the valves of the mollusk. After eating, the connective tissue softens, becomes elastic, and the starfish straightens. Sea urchins, by changing the stiffness of connective tissue, can fix the position of spines, which are used to repel predators or for anchoring in rock crevices. Under stressful conditions, brittle stars and sea cucumbers spontaneously reject (autotomize) the rays or throw out internal organs through local softening of the connective tissue. In extreme cases, when some sea cucumbers are removed from the water into the air, their body completely softens, spreads out, and the animal dies. Although the integument of echinoderms contains muscles, nerves and other types of cells, it is the extracellular matrix of connective tissue that changes stiffness. This matrix contains the endings of nerve cells, and there are probably two types of nerves: the action of some makes the matrix rigid, the action of others softens it. The stiffness of the matrix is affected by changes in the concentration of Ca 2+ and other cations. In general, an increase in Ca 2+ concentration stiffens the matrix, while a decrease softens it. Ca 2+ can participate in the formation of bridges between macromolecules in the matrix.
Digestive system
A starfish can open the shell of a bivalve mollusk and digest it right in it.
The body cavity is filled with coelomic fluid containing numerous amoeboid cells. These cells absorb waste products and foreign bodies and exit the body through the integument. Thus, they perform excretory and immune functions.
Ambulacral system
The sea urchin moves with the help of its ambulacral legs.
Madrepore plate
Perihemal and circulatory systems
The perihemal system is a collection of canals and cavities (sinuses) surrounding the animal’s circulatory system. The circulatory system is poorly developed and is a system of cavities in the connective tissue (lacunae) that do not have an endothelial lining. Each beam contains two radial perihemal canal, in the partition between which is located radial blood vessel. Radial vessels enter oral blood ring, lying in the partition between two ring perihemal canals. Genital sinus surrounds aboral blood ring and the genital stolon. Two blood rings connected axial organ, surrounded left and right axial sinuses.
Axial complex
The axial complex of organs is located in one of the interradii of echinoderms. It consists of organs from different systems:
- Petrosal canal connecting the annular ambulacral canal with the madrepore plate;
- An axial organ, inside of which there is a network of blood vessels;
- The left axial sinus is part of the coelom connecting the internal annular perihemal canal with the right axial sinus;
- The right axial sinus, capable of contracting rhythmically and thereby promoting the movement of blood in the vessels, that is, performing the functions of the heart;
- The genital sinus is a section of the coelom containing the sex cord, which consists of immature germ cells.
Nervous system
Phylogenetic origin
Fossil crinoids
The common ancestor of all Deuterostomes was a bilaterally symmetrical free-living animal with three pairs of coelomic sacs. This is indicated by the presence of a developmental stage that is similar in all Deuterostomia. In echinoderms, this stage corresponds to the dipleurula larva. The appearance of the first echinoderms is associated with the transition of this hypothetical ancestor to a sessile lifestyle and its acquisition of radial symmetry.
The oldest representatives of echinoderms belong to the class Carpoidea. They lived from the Cambrian to the Lower Devonian. They led a sedentary lifestyle, but did not yet have radial symmetry. The body was covered with plates, the mouth and anus were located on the side facing away from the substrate. The internal organs were located asymmetrically. Among class representatives Cystoidea(spherical) radial ambulacral grooves appeared around the mouth, intended for collecting food from the water column. The rest originate from the balls Pelmatozoa: Class Blastoidea(sea buds), which is characterized by powerful development of jointed arms, modern sea lilies and class Edrioasteroidea, in which free-living species appeared. First Eleutherozoa, combining the features of modern sea stars, brittle stars and sea urchins, belonged to the class Ophiocistia. From them came the modern representatives of the subtype. Holothurians, which have retained a number of primitive characters (madrepore plate and gonopore on the oral side, one gonad), originate directly from globuloids.
Echinoderms are well preserved in fossil form due to the fact that their internal skeleton consists of calcareous sclerites.
Classification
Phylum Echinodermata (echinoderms)
- Subtype Pelmatozoa(pelmatozoa, attached)
- Class †Carpoidea - carpoideans
- Class †Cystoidea – globuloids, cystoids, or sea bladders
- Class †Blastoidea - sea buds, or blastoidea
- Class Crinoidea- sea lilies
- Class †Edrioasteroidea - edrioasterodeans
- Subtype Eleutherozoa(eleutherozoa)
- Class † Ophiocistia - ophiocystia
- Class Asteroidea- sea stars
- Class Ophiuroidea- brittle stars
- Class Echinoidea- sea urchins
- Class Holothuroidea- holothurians
Notes
References
- Biological encyclopedic dictionary edited by M. S. Gilyarov et al., M., ed. Soviet Encyclopedia, 1989.
- Zoology of invertebrates. Dogel V. A., 1981.
- Course of comparative embryology of invertebrate animals. Ivanova-Kazas O. M., Krichinskaya E. B., 1988.
Links
- Virtual Echinoderm Newsletter
- Photos of echinoderm larvae
- Tree of Life Web Project: Echinoderms
- Classification of modern echinoderms (California Academy of Sciences) (English)
- Classification of echinoderms (University of California Museum of Paleontology) (English)
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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 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. The starfish, with the help of a complex system of sensory organs (at the tip of each ray there is an eye, a branched nervous system, and receptor cells that respond to mechanical and chemical stimuli are located on the entire surface of the body) feels confident and calm on the seabed, even being a predator that eats 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 a starfish 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 connected into one system in the center of the star (disc): in the stomach the digestive system is combined and opens with the mouth, the nervous system is connected into a nerve ring, the ambulacral system is connected by a 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.
The values of summer and winter sea water temperatures off the coast of Primorye differ significantly, and these differences are greatest in the littoral zone. In winter, the surface of the water freezes to -2 ºС, and in summer it warms up to 25 ºС 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? Everything is very simple, it penetrated from the 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. As a result, marine inhabitants of the bottom turn out to be practically invulnerable, being consumers (SOM - consumers of organic matter) of the 2nd order.