Sea stars- These are very unusual animals that live in the seas and oceans. They are invertebrates, belong to the phylum echinoderms and are very similar to stars, as they have rays diverging in different directions. Most often, the sea star has five rays, but there are species with three, four and six rays. The color of the body is often very bright and varied; on the surface there are special hard plates with needles or spines. The sizes of stars vary greatly and can range from 2 cm to 100 cm, but most stars have a diameter of about 20 cm.
Spreading
Starfish are widely distributed around the globe. They can be found in all oceans and seas and in all climatic zones, but in warm waters There are more starfish than in cold waters, and in fresh waters they are not found at all.
These animals prefer a bottom lifestyle, often live in shallow water, but can also live at depth, but not deeper than 8.5 km.
Now on earth there are 1.6 thousand species of starfish.
Nutrition
Almost all starfish are predators. They mainly feed on marine invertebrates - worms, mollusks, sponges, barnacles, corals and others. Some deep-sea starfish feed on the mud they find on the bottom.
The digestive system of starfish is quite unique. Their mouth opening is located on the ventral side, and two stomachs extend from it. One stomach has the ability to turn outward and envelop the victim, and the second stomach has ten processes that are located inside the rays of the starfish. This unusual digestive system allows the star to eat prey that is larger than itself.
Lifestyle
Starfish are slow, sedentary animals. They usually crawl lazily along the bottom, lie still, or may climb rocks and corals in search of prey. Their movement speed is very low - 10-30 cm per minute. Stars are considered sedentary animals. As a rule, they move no further than 0.5 km from their usual place of residence.
In their development, stars go through several stages of development. From the eggs that adults throw into the water, larvae are first formed and then they gradually turn into an adult starfish. Some species of starfish carry larvae in special brood pouches on their bodies.
Starfish can live 20 years or more.
- Starfish don't have a brain.
- Instead of eyes, starfish have light-sensitive cells located at the tips of their rays.
- Starfish are capable of regeneration - from a detached ray, a new star can develop.
Brief information about starfish.
Sea stars- amazing creatures that look so beautiful on the seabed! Today, friends, we want to tell you a little about them, starting with their general characteristics.
Description of starfish
Echinoderms There are about 1600 species, but today we will list the main ones. The size of the stars ranges from 1 mm to 25 cm, it all depends on the species. Of course, each view is beautiful and colored in its own way, some stars are bright, others are barely visible in the sea. The rays of the star serve as digestion, because it is in them that the processes of both the genital organs and the stomach itself are located. The starfish also has legs and a mouth!
The stars feed plankton, detritus, barnacles, clams, oysters, mussels and even corals! A life expectancy its average age is 20 years.
Interesting facts about starfish
The legs of a starfish are usually equipped with suction cups to make it convenient to move along the seabed.
Most starfish are predators
Dioecious stars
Stars reproduce right in the water, sweeping out both sperm and eggs.
Usually the fertilized “larva” is attached next to the parent, but some carry the baby in a special pouch
HABITAT AND SPECIES OF SEA STAR
Types of starfish
1. Ludia two-needle
2. Patiria comb
3. Solaster pacific
4. Henricia Hayashi
5. Lysastrosoma antisticta
6. Dystolasteria causticus
7. Letasteria nigra
8. Aphelasteria japonica
9. Eusteria spinosa
10. Eusteria reticularis
11. Common Amur star
Where do starfish live?
Sea stars are the oldest group of animals that have survived to our age! And strangely enough, a marine representative can be found in almost every salty sea and every ocean. By the way, it is in those seas where there is normal salinity that starfish can be found on the shore! It is for this reason that humanity has known about them since ancient times.
VIDEO: ABOUT SEA STARS IN THIS VIDEO, WE INVITE YOU TO WATCH A DOCUMENTARY ABOUT SEA STARS
They raise many questions, among which the following are of particular interest: “What does a starfish eat?”, “For whom does it pose a mortal threat?”
Stars on the seabed
These extraordinary decorations of the seabed have existed on the planet for quite a long time. They appeared about 450 million years ago. There are up to 1600 types of stars. These animals inhabit almost all seas and oceans of the earth, the water of which is quite salty. Stars do not tolerate desalinated water; they cannot be found in the Azov and Caspian Seas.
Animals can have rays from 4 to 50, sizes range from a few centimeters to a meter. The lifespan is about 20 years.
The sea inhabitants do not have a brain, but on every ray there is an eye. The organs of vision resemble insects or crustaceans and distinguish between light and shadow well. Many eyes help animals hunt successfully.
Stars breathe almost through their skin, so it is very important for them to have a sufficient amount of oxygen in the water. Although some species can live at decent depths of the ocean.
Structural features
It is interesting how starfish reproduce and feed. Biology classifies them as invertebrate echinoderms. The starfish does not have blood as such. Instead, the star's heart pumps through the vessels sea water, enriched with some microelements. Pumping water not only saturates the animal's cells, but also by forcing fluid into one place or another helps the star move.
Starfish have a ray structure of the skeleton - rays extend from the central part. The skeleton of sea beauties is unusual. It consists of calcite and develops inside a small star from almost a few calcareous cells. What and how starfish feed largely depends on the characteristics of their structure.
These echinoderms have special pedicellaria on their tentacles in the form of tweezers at each tip of the outgrowth. With their help, the stars hunt and clean their skins from debris clogged between the needles.
Cunning hunters
Many people are interested in how starfish eat. Briefly about their structure digestive system can be found below. These amazing beauties create the impression of complete security. In fact, they are sea predators, voracious and insatiable. Their only drawback is their low speed. Therefore, they prefer a stationary delicacy - mollusk shells. The starfish eats scallops with pleasure and doesn’t mind eating sea urchin, sea cucumber and even a fish that carelessly swam too close.
The fact is that the starfish has practically two stomachs, one of which can turn outward. An unwary prey, captured by the pedicellariae, is transferred to the mouth opening in the center of the rays, then the stomach is thrown over it like a net. After this, the hunter can release the prey and slowly digest it. For some time, the fish even drags its executioner along with it, but the victim can no longer escape. Everything that a starfish eats is easily digested in its stomach.
She acts somewhat differently with shells: she slowly approaches the dish she likes, entwines the shell with her rays, places her mouth opening opposite the slit of the shell and begins to move the shells apart.
As soon as even a small gap appears, the external stomach is immediately pushed into it. Now the sea gourmet calmly digests the owner of the shell, turning the mollusk into a jelly-like substance. This fate awaits any eaten victim, no matter whether the starfish feeds on a scallop or a small fish.
Features of the structure of the digestive system
The predator does not have any devices for capturing prey. The mouth, surrounded by a ring lip, connects to the stomach. This organ occupies the entire interior of the disc and is highly flexible. A gap of 0.1 mm is enough to penetrate the shell doors. In the center of the aboral side, a narrow, short intestine opens, extending from the stomach. What a starfish eats largely depends on the unusual structure of its digestive system.
Love of the stars at the bottom of the ocean
Most starfish are heterosexual. During love games, individuals are so busy with each other that they stop hunting and are forced to fast. But this is not fatal, because in one of the stomachs these cunning creatures try to deposit nutrients in advance for the entire duration of mating.
The gonads are located in stars near the base of the rays. When mating, the female and male individuals connect the rays, as if merging in a tender embrace. Most often, eggs and male reproductive cells end up in sea water, where fertilization occurs.
If there is a shortage of certain individuals, stars can change sex to maintain the population in a certain area.
These eggs are most often left to their own devices until the larvae hatch. But some stars turn out to be caring parents: they carry eggs and then larvae on their backs. U certain types For this purpose, during mating, starfish appear on their backs with special sacs for eggs, which are well washed with water. There she can remain with the parent until the larvae appear.
Reproduction by division
A completely extraordinary ability of starfish is reproduction by fission. The ability to grow a new ray arm exists in almost all animals of this species. A star grabbed by a beam by a predator can throw it away like a lizard's tail. And after a while, grow a new one.
Moreover, if a small particle of the central part remains on the beam, after a certain time a full-fledged starfish will grow from it. Therefore, it is impossible to destroy these predators by cutting them into pieces.
Who are starfish afraid of?
Representatives of this class have few enemies. Nobody wants to mess with the poisonous needles of sea celestials. Animals are also able to secrete odorous substances to scare away particularly voracious predators. In case of danger, the star can bury itself in silt or sand, becoming almost invisible.
Among those who feed on starfish in nature, large seabirds predominate. On the shores of warm seas they become prey for seagulls. In the Pacific Ocean, cheerful sea otters are not averse to feasting on the star.
Predators harm underwater plantations of oysters and scallops - what the starfish eats. Attempts to kill animals by cutting them into pieces led to an increase in the population. Then they began to fight them, bringing the stars ashore and boiling them in boiling water. But there was nowhere to use these remains. There have been attempts to make fertilizer from animals that also repels pests. But this method was not widely used.
Starfish are 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 of 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 starfish, reproduction by division is a normal form of asexual reproduction. In this case, softening occurs in the division plane connective tissue. 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 juvenile star primordium 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 1mm in diameter, detaches 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.