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all Crustacea - from planktonic small fry to a huge Japanese crab-spider - have one common feature: the rigid jointed external skeleton serving by it by a skeleton and protection.

Crustacea Crustacea - one of several classes of the animals possessing jointed, similar to shell, a skeleton which serves not only a skeleton for muscles and an internal, but also protection against damages and enemies. All these animals are called as arthropods, or Artbropoda, because from molluscs living in bowls - for example, mussels and serdtsevidok - differ mobile sustavchatymi finitenesses.

Them ekzoskelet represents utolshchennuju the become horny fabric, or kutikulu which chemical compound is distinguished at different animals. So, at insects the armour consists basically of chitin - an elastic horn material. At many large sea Crustacea like crabs and lobsters the chitin strengthened by calcium forms a firm calcareous armour.

Difficulties of growth

Growth Process is interfaced to considerable difficulties and even risk. At animals with an internal skeleton - for example, at us - bones simply grow in itself together with muscles and an internal. But the chitinous or calcareous armour chlenistonogogo beings does not grow, and keeps time for ever the got form and the size. And as muscles and an internal of an animal continue to grow, pressure in an armour will accrue too while it will not break up to pieces.

In kutikule there are the fragile sites which are breaking up when pressure from within reaches a known limit. Under an old armour always disappears new with igolochki a suit.

When comes it is time to change become close clothes, the animal involves air or water, and the old armour bursts, giving way to the newcomer shining kutikule. While it has not hardened, the animal is inflated as it is possible more strongly. Thanks to it the new armour will be a little velikovat to the owner, and there will be a place for the further growth.

a body Structure

Crustacea At some arthropods like spiders and insects the number of feet is accurately defined (6 - at insects, 8 - at spiders), meanwhile as at Crustacea in this business reigns full raznoboj. At this class of animals each segment of a body is allocated by own pair finitenesses of what it is easy to be convinced, having got accustomed to an ordinary wood louse.

The Body of this similar to a being battleship consists of a chain of the sites covered with a thin armour, each of which is supplied by pair finitenesses. However not all of them carry out identical functions. If pads of first seven segments following a head, are used for walking finitenesses of other of five have turned to respiratory bodies. The pair located on last segment, possibly, serves as an organ of touch, as well as two pairs aerials growing on a head.

At first sight all parts of a body of a wood louse seem identical, but, having got accustomed more close, we will see that last six members form the tail part as though inserted in last from seven "§юфшыіэ№§" segments. At many Crustacea this prominent feature is more brightly expressed, and so that "§юфшыіэ№х" segments grow together with a head and form golovogrud. A typical example of such structure is the shrimp.

The Armour covering golovogrud, is called as a guard. At some Crustacea, for example, at crabs, it wide and flat; at others has the form of the rounded off capsule similar to an oyster cockleshell. However, despite all distinctions, main principle of a structure of a body remains invariable - at each segment on one pair finitenesses. If in a single whole seven segments at an animal will be seven pairs feet have grown together.

Floating and drifting

Except for a wood louse, almost all Crustacea live in the water environment. One creep on a sea or river bottom, others are attached to stones, but many simply drift on a current in uncountable community of the same small animals and plants which is called as a plankton. So some live the most primitive rachki, for example, zhabronogi. These inhabitants of time fresh reservoirs from them 20 and it is more accurate the issued elements of a trunk, each of which is supplied by own pair listovidnyh finitenesses, have kept a multisegment structure of a body of the ancient ancestors. All finitenesses, being more or less identical, carry out set of functions. ZHabronog floats headfirst, moving to a uniform rhythm all legs, and numerous resnichki filter from water of a particle of food. When zhabronog makes a start all pads back, the food with water stream gets on a sticky layer on forward pads which direct it to a mouth. The same finitenesses operate as a gill, absorbing oxygen from water through thin kutikulu. Therefore zhabronogi and their relatives listonogi are called "црсЁюэюушьш" or Brancbiopoda.

Others zhabronogie look absolutely differently. The armour (guard) of a tiny water flea beetle, or dafnii, living in ponds and lakes, covers almost all its body, leaving opened only a head. Its pads operate as a gill because of what dafnija too it is carried to group zhabronogih, but it moves, grebkami powerful second pair of aerials, banishing water rich with food through covered plumose shchetinkami filtering device of the finitenesses.

All on a kind

The Transparent external guard dafnii allows to see all its internal, including vyvodkovuju the chamber in which berries develop. Dafnii, as well as the majority of Crustacea, — raznopolye beings, but the female is quite capable to deduce posterity without pairing, in so-called process partenogeneza. With approach of spring when water is rich with a forage and conditions for growth and reproduction are ideal, population dafny in a reservoir sharply increases and consists almost entirely of females. But in the end of summer and in the autumn the changed living conditions impulse to increase in number of males. Coupling with females, they impregnate the berries steady against drying and a frost and capable to survive in the winter when all population dies out. Next spring from them there are larvae, and all cycle repeats at first.

It is easy to find set of small elementary Crustacea In any fresh-water reservoir with long aerials growing on each side. It veslonogie - members of a numerous class which totals over 8400 kinds.

a Food through the filter

The Most part of year sea veslonogie rachki eat other planktonic animals, but during a season "тхёхээхую чтх=хэш " a microscopic phytoplankton they are switched to a filtrational food, getting water rich with a forage in the second pair aerials and filtering it through kozhistoe resheto modified finitenesses.

Approximately during the same time they promptly breed, and, by some estimations, on a share veslonogih rachkov the great bulk of a world's reserve of animal protein is necessary. They are the main power supply of the majority of other sea inhabitants.

Not all veslonogie freely float in thickness of water. Some - for example, karpovye louses - have safely turned to the parasites eating blood of the owners and armed with hooked pads inadvertently not to fall off a feeding trough. Whales are exasperated too with the rachki-parasites in length to 30 Other kinds see differ narrower specialisation and are arranged on life in the fish gills, being fed with the blood circulating in thin branchiate fabrics.

the Live crust

Every possible kinds usonogih rachkov which huge colonies render habitable reefs and topljaki on coast of all seas of the world have even better adapted to external conditions. At first sight sea acorns are similar on molluscs-saucers. Actually it rachki, selected a sedentary life on stones and filtering food from surrounding water.

the Dangerous inhabitancy

The Life on sea coast - business rather unsafe. Any local inhabitant can be broken surf waves, is crushed by casually fallen down stone or simply to dry up during outflow. Therefore here not to do without reliable protection. The sea acorn has solved this problem, having grown on the head kutikuly some the firm limy plates forming together a bowl in the form of a cone. The bowl is tightly attached to an underwater rock, and the animal eats through a small aperture in its top, getting food from water six steams hooked shchetinistyh legs. For the period of outflow rachok involves legs and densely closes a bowl several plates to keep inside water.

Sea acorns - germafrodity. For reproduction everyone moustached rachok uses a long tube through which enters sperm to the neighbours, and those store oosperms in a bowl while from them microscopic and rather quick larvae-naupliusy will not develop. Everyone nauplius goes to free swimming in thickness of a plankton where about one month lives and eats more likely as veslonogy rachok. After that it is attached to a rock and turns to the adult settled individual.

Mobile lichinochnaja the development stage has for moustached rachkov huge value for to its help there is a moving of all kind. This stage of their life name also "фшёяхЁёэющ ¶рчющ". The set of others concerning inactive Crustacea, including cancers, crabs and lobsters uses the Same system. Larvae-naupliusy of all these kinds some time wander in a plankton thick, before will settle on a sea-bottom to begin transformation into the adult individual.

Similarly veslonogim rachkam, not all representatives of group usonogih are entered in uniform classical structure. We will tell, sea ducks conduct about the same way of life, but their lamellar cockleshells grow on short small stalks and, without having reliable protection, cannot live without water. Still the big originality rachki-parasites like Sacculina carcini differ usonogie. Their larvae first freely float in thickness of water, but adult individuals are attached to a crab and start "ъюЁэш" in its body, eating juice of the owner.

Polzuny and shchelkuny

The Overwhelming majority of Crustacea belongs to a subclass Malacostraса, including a number of widely known groups: wood lice, tolstogolovok, shrimps, lobsters and crabs. Some of these animals are able to float, but many possess strong hodilnymi feet and live either on a land, or at a sea or river bottom. The given circumstance has allowed some kinds to grow till rather impressive sizes. These ground animals have refused filtering of food from water and some steels active predators eat the fossils. Thus at many the powerful claws, capable to suffice and break off extraction have developed.

At all land and sea wood lice much in common in appearance and habits. These are multisegment and mnogonogie ashmen of sea coast and crude corners of a land. Sea wood lice - mainly the water animals, managed to adapt to a survival above inflow level. Finitenesses of their back segments have turned to the gills storing own water-supply while they are occupied by searches of a forage along a surf strip. They require constant humidifying, but perish, for a long time it having appeared under water.

Wood lice

On a step forward have promoted in wood louse development. Definitively having left the water environment, all of them require constant humidifying, therefore always lodge in crude places. They breathe gills in the same way as their sea relatives, but the respiratory system should be constantly covered by a thin film of water in which oxygen is dissolved. In back finitenesses of some kinds of wood lice primitive respiratory tubes in which damp environment the arrived oxygen is dissolved were generated.

Distant relatives of wood lice, ravnonogie or bokoplavy, is basically sea animal, living at the bottom or parasitizing on other Crustacea or fish. Unlike the majority of Crustacea, they do not have planktonic stage of development of larvae, and thanks to it one group of this group - wood lice - could lodge on a land.

One of kinds ravnonogih is called as a fresh-water shrimp though and considerably differs from the present shrimp with its accrete golovogrudju, well developed pair claws and four steams strong hodilnyh feet. On total number of finitenesses the present shrimps and their relatives are named dekapodami or desjatinogimi. This group includes shrimps, cancers, lobsters and crabs.

In close relationship with desjatinogimi consists kril - planktonic krevetkopodobnoe a being, in infinite quantities living in the southern seas approximately the same as veslonogie rachki in northern. Kril eats a phytoplankton (microscopic seaweed) which breeds under the round-the-clock sun of the Antarctic polar summer much. As veslonogie rachki in the north, it is the main source of animal protein in the environment of the dwelling.

If kril floats in the top layers of ocean desjatinogie Crustacea walk about on a bottom or a shore, only being occasionally started up, by swimming. For example, there are the shrimps who have chosen for habitation sandy beaches, located below an inflow line where they are fed with the fossils cast ashore. Their claws consult almost with everything that suits in food, including with malkami and others small rachkami. Shrimps-cleaners living in the tropical seas are curious. They as real footmen serve large big fishes, clearing them of parasites. Potential clients quickly find them among stones and coral thickets on bright striped raskraske.

the Main thing - in time to be washed off

The Usual shrimp floats by means of five pairs finitenesses growing from a paunch, but in need of fast flight instantly makes a start back blow of a fanlike tail. Portly lobsters and fresh-water cancers for powerful fossilized armours of these heavyweights do not allow them to keep afloat use the same reception. Thick kutikula a lobster does its almost impregnable, but among desjatinogih is and less protected kinds. We will tell, cancers-eremites hide a soft paunch in bowls of sea molluscs, having bent it under the form of the dwelling. However, in process of growth the cancer should look for new, more spacious apartment. The eremite keeps the house on itself specially adapted finitenesses and at the slightest threat hides inside, having covered an input with an enormous right claw.

At the majority of crabs firm enough paunch nevertheless is curtailed under a wide armour golovogrudi. Thanks to it the center of gravity is displaced forward and it appears directly over feet of a crab, allowing it to hold balance better, than to a lobster. Besides, moving sideways, the crab uses the finitenesses for so it is more convenient to them to move much more effectively. As a result the crab amazes with the quickness, running much faster many relatives so, and to survive to it easier.

Many kinds of Crustacea live on a sea-bottom, being fed with fossils or hunting, but some, especially green crabs, crabs-ghosts and attracting crabs, often meet and ashore. Someone even has managed to locate on a land. Land crabs breathe the same as wood lice, dissolving oxygen in a film of the moisture covering gills. But their larvae - as well as larvae of sea relatives - float in a plankton, therefore for deducing of posterity they come back in the sea.