Starfish ( lat. Asteroidea - from the Greek. Ἀστήρ " star ") - a class of invertebrate type echinoderms . About 1600 modern species are known (150 in Russia) [1] .
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Starfish and their larvae. Illustration from Ernst Haeckel's book Kunstformen der Natur , 1904 | |||||||||||||||||
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Asteroidea Blainville , 1830 | |||||||||||||||||
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Content
Biology
Star-shaped or pentagonal echinoderms . The size of the stars ranges from 2 cm to 1 m, although most have a magnitude of 12-25 cm. Many species are brightly colored.
These are sedentary animals, most often having five rays, however, there are also specimens with three, four or six rays [2] .
Rays, or hands, are organs extending from the central flat or slightly convex disk of a starfish. When the rays are shortened, the body shape approaches a pentagonal. The rays enclose the digestive outgrowths of the stomach and the processes of the genital organs; inside the beam is a longitudinal row of vertebrae . The skin is equipped with correctly arranged skeletal plates, which are armed with spikes and needles, sometimes - pedicellaria . Ambulacral legs sit in open grooves, extending along the underside of the rays to the mouth. The legs are flexible tubular outgrowths, usually with suction cups at the end, and are driven by water pressure in the internal channels and ampoules of the ambulacral system . The mouth is located in the center of the abdominal side, the anus on the dorsal side; madrepor plate - on the dorsal side .
The digestive system is unique. Above the mouth inside the disc are two gastric sacs; ten digestive (hepatic) outgrowths leave the upper (pyloric), two in each hand. The lower stomach is able to evert, enveloping and partially digesting food.
Sense organs : red eye spots at the ends of the rays and tactile endings of the skin.
Starfish have a highly developed ability to regenerate : restore torn rays. In addition, part of the starfish, which includes a fairly large piece of the central disk, can grow into a full-fledged animal. Particularly noteworthy is the genus Linckia , in whose representatives the detached ray is able to develop into a new organism.
The life expectancy of a starfish is 20 years or more [3] .
Lifestyle & Nutrition
Starfish are benthic animals crawling with ambulacral legs, usually equipped with suction cups. Everywhere they live in oceans and seas (except for desalinated areas) to a depth of 8.5 km.
Most starfish are predators that feed mainly on mollusks , sea ducks , polychaete worms, and other invertebrates. Some feed on plankton and detritus ; There are species that can catch prey with the help of pedicellaria .
T. Thornton describes the way starfish and ophiurs protect a small population of plate-branchial mollusks, which are their main food, from extinction, saving themselves from starvation. The mollusk larvae are so small that starfish could easily destroy them, but at this time they begin a period of starvation, lasting from 1 to 2 months - until they grow by 2-3 orders of magnitude - after which their appetite "turns on" [4] .
Having discovered a bivalve mollusk , a starfish grabs its shell with its hands, sticks to it with ambulacral legs and, due to muscle tension, pushes the cusps apart. The lower stomach turns out, penetrating into the shell, envelops the soft parts of the mollusk and digests without swallowing. The liquefied food is then drawn into the body.
Some starfish (for example, Asterias rubens ) cause damage by destroying commercial mollusks ( oysters , mussels , etc.); others ( crown of thorns , Acanthaster planci ) eat reef-forming corals .
Reproduction and development
Starfish are predominantly dioecious . Starfish usually have two gonads in each ray, opening at the sexual time at the base of the ray; they multiply by extruding eggs and sperm into the water. After fertilization, a free-floating larva ( bipinnaria , brachiolaria ) forms , which usually attaches close to an adult of the same species and undergoes metamorphosis under the influence of its pheromones. Some species - hermaphrodites - carry juveniles in a special hatcher bag or cavity.
In Culture
- A starfish named Patrick is one of the main characters in the popular animated series SpongeBob SquarePants .
Gallery
Extinct species, Jurassic
Pacific Ocean, USA, Oregon
Asterias rubens , White Sea , Russia
Indian Ocean , Tanzania
Pacific Ocean Canada
Pacific Ocean , Papua New Guinea
Pacific Ocean , USA
Yellow Sea , South Korea
Pacific Ocean , Australia
Indian Ocean , Thailand
Norwegian Sea , Norway
Pacific Ocean , Australia
Pacific Ocean , Australia
Indian Ocean , Tanzania
Hong Kong Market
Notes
- ↑ Data on the number of species for Russia and the whole world
- ↑ Four-beam starfish discovered off the coast of Primorye
- ↑ Akimushkin I.I. Animal World. Invertebrates. Fossil animals. - 3rd ed. - M .: Thought, 1995.- S. 219. - 15,000 copies. - ISBN 5-244-00804-8 .
- ↑ Alexander Ugolev. Theory of adequate nutrition and trophology .. - P. chapter 1.5. Population, environmental and evolutionary problems of trophology. The biosphere is like a trophosphere ..
Literature
- Invertebrate Zoology: Functional and Evolutionary Aspects: A Textbook for Stud. universities: in 4 vols. T. 4. Cycloneurals, tentacle and second-edged / Edward E. Ruppert, Richard S. Fox, Robert D. Barnes; under the editorship of V.V. Malakhova - M .: Publishing Center "Academy", 2008.
- Starfish: Biology and Ecology of the Asteroidea / Lawrence, JM. - Johns Hopkins University Press, 2013 .-- ISBN 978-1-4214-0787-6 .
- Atlas of starfish of the Far Eastern seas of Russia . - Vladivostok, 2010.
Links
- Starfish // Brockhaus and Efron Encyclopedic Dictionary : 86 t. (82 t. And 4 ext.). - SPb. , 1890-1907.