Cinequiferous chords. Class crustaceans. Higher and lower cancers are the intermediate hosts of human helminths. A variety of biological forms of lower and higher crustaceans
Cruise Class (Crustacea)
Class crustacea (crustacea) includes very diverse arthropods. These include, often no similar to each other and the appearance, and in the lifestyle of animals, like crabs and wets, river crayfish and shrimps, raches and carp lice, lobsters and water fleas ... and since adult crustaceans are very diverse In the form, then give them a brief description, clearly distinguishing them from other groups of animals, almost impossible. Therefore, evolutionary (genetic) related links between different representatives of the class are established only by the peculiarities of their larval development. And he, in turn, usually includes complex metamorphosis, in which only the first larch stage - the nude - the overall for all crustaceans. But some others, but in some cases, and everything, including the first may not be absent, and then a copy of an adult animal is immediately hatching from the fertilized egg, but only a miniature ...
Some edible and harmful types of crustaceans are known to a person with deep antiquity, but most of the representatives of this class are known only to narrow specialists. As it turned out, crustaceans belong to one of the most numerous on our planet. Currently, scientists described more than 25,000 their species. At the same time, most types of crustaceans live in the seas and oceans, so they are sometimes called "marine insects" for abundance and variety. At the same time, many types of crustaceans also live in fresh waters and on land. Therefore, they can practically be found in all reservoirs: and under ice in polar areas, and in hot springs with a temperature of up to 50 ° C, and in the deserts, and at depths to 6 km, and the tops of tropical trees.
Great and economic importance of crustaceans. At the same time, crabs, lobsters, crayfish and shrimp are of great importance, which man directly uses. But numerous fine forms that are floating in the surface of the water bodies in the composition of zooplankton and often barely distinguishable with the naked eye, constitute the main link of a number of food chains. It is these tiny crustaceans that are a link between microscopic plankton algae with fish, whales and other large commercial animals. Without small crustaceans, which convert herbal cells into an easily digestible animal feed, the existence of most of the water fauna's representatives would be almost impossible.
Among crustaceans, quite a few and harmful species, which are damaged by the farm person or his health in one way or another way. So, the drilling forms of crustaceans, such as cancer-tree, do moves in wooden port facilities and other underwater buildings. On the bottoms of the vessels form powerful rates of sea acorns and sectorals that interfere with shipping. Some types of crabs, river crayfish and some other crustaceans are in the tropics (and in the Far East of Russia) carriers of human diseases, while other crustaceans, like wickers and shield, often harm vegetation, in particular rice sowing, or bred maritime species.
Cruise - ancient aquatic animals having a complex dismemberment of the body covered with a chitine shell, with the exception of wetting wets. They have up to 19 pairs of articular legs performing various functions: capture and grinding of food, movement, protection, pairing, lagging with juveniles. These animals feed with worms, mollusks, lower crustaceans, fish, plants, and crayfish eating and dead prey - the corpses of fish, frogs and other animals, performing the role of sanitation reservoirs, especially since they prefer very clean fresh water.
Lower crustaceans - Daphnia and cyclops, representatives of zooplankton - serve food for fish, their fry, toothless whales. Many crustaceans (crabs, shrimps, lunguhsts, lobsters) are commercial or specially breeding animals.
The Red Book of the USSR introduced 2 types of crustaceans.
general characteristics
From a medical point of view, some types of plankton crustaceans are of interest as the intermediate hosts of helminths (cyclops and diaptomes).
Until recently, the crustacean class was divided into two subclasses - lower and higher crayfish. The subclass of the lower cancers was combined with leaf-legs, jaw and seashell cancers. Currently it is recognized that such an association is impossible, since these groups of cancers are different in their origin.
In this section, the class crustaceans will be considered on the old classification.
The body of crustaceans is divided into headband and abdomen. The headband consists of head and chest segments that merge into a common, usually undisturbed body department. The belly is more often dismembered.
All crustaceans have 5 pairs of head limbs. The first 2 pairs are represented by segic mustache; These are so-called antennas and antennas. They carry the signs of touch, smell and equilibrium. The following 3 pairs are the mouth limbs - serve to capture and grind food. These include a pair of upper jaws, or Mandibul, and 2 pairs of the lower jaws - Maxill. Each breast segment carries a pair of legs. These include: Nogility, participating in retention of food, and locomotor limbs (walking feet). The belly of the higher crayfish also carries the limbs - swimming legs. There are no fewers.
For crustaceans, a two-way structure of the limbs is characterized. They distinguish the basis, outer (dorsal) and inner (ventral) branches. Such a structure of the limbs and the presence of gills of gill growing confirms the origin of crustaceans from nullifying ring worms having two-track parapody.
In connection with the evolution in the aquatic environment, water respiratory organs developed in crustaceans - Zabra. They are often growing on the limbs. Oxygen is delivered by blood from the gills to the fabrics. Lower raks have colorless blood called hemolymph. The highest cancers have real blood containing oxygen-binding pigments. River cancer blood pigment - hemocyanin - contains copper atoms and gives blood blue.
Options serve one or two pairs of modified metanephridium. The first pair is localized in the front of the pitchfork; Its duct opens at the base of the antennas (antennal glands). The duct of the second pair opens at the base Maxillars (maxillary glands).
Crustaceans, with rare exceptions, separatogs. Usually develop with metamorphosis. From the egg there is a larva with a nauplius with an non-gentle body, 3 pairs of limbs and one unpaired eye.
- Entomostraca subclass (lower racks).
Lower cancers live in fresh waters and in the seas. They are important in the biosphere, being an essential part of the food diet of many fish and cetacean. Miscealthcare (Copepoda), which serve as intermediate hosts of human helminths (Diffilobotry and Rishta) are the greatest importance. They are found everywhere in ponds, lakes and other standing reservoirs, inhabiting water.
general characteristics
The body of the launcher is dissected for segments. A sophisticated head carries one eye, two pairs of antennas, the oral apparatus plus a couple of legs-jaws. One pair of antennas is much longer than the other. This pair of antennas is strongly developed, their main function is movement. Also often they serve to hold female male during mating. Breasts of 5 segments, breast legs with swimming bristles. The abdomen of 4 segments, at the end - a fork. At the base of the female abdomen 1 or 2 egg bag, in which eggs develop. From eggs come out the larvae of the naupals. Non-supels with their own species are absolutely not like adult rashes. Development is accompanied by metamorphosis. The grinding wraps feed on the organic residues, the smallest water organisms: algae, infusories, etc .. dwell in reservoirs all year round.
The most common genus diaptomus (Diaptomus)
Daptoms are inhabited in the open part of the reservoirs. The size of the label is up to 5 mm. The body is covered by a rather solid shell in connection with which he is reluctant to eat fish. Color depends on the nutritional base of the water branch. Daptomes have 11 pairs of limbs. Antennas Soytvists, antennas and legs of breast segments Twilight. Especially long the lengths reaches the antennas; They are longer than the body. Widely scattering them, the diaptomes are soaked in water, the chest limbs determine the jump-shaking movements of the raschkov. The mouth limbs are in constant oscillatory movement and customize the particles weighted in the water. Both sexes take part in the reproduction diaptoms. In the diaptomy females, in contrast to the cyclop females there is only one egg bag.
Types of genus Cyclops (cyclops)
inhabited mainly coastal zones of water bodies. They are shorter than that of diaptoms, and participate along with breast legs in moving jumps. The coloring of cyclops depends on the type and color of food, which they feed (gray, green, yellow, red, brown). Their size reaches 1-5.5 mm. Basis take part in reproduction. Fertilized eggs female in egg bags (in cyclops there are two) attached at the base of the abdomen.
In its biochemical composition, the grinding races stand in the top ten of high-protein feeds. In the aquarium "Cyclops" most often used to feed the grained juvenile and small in size of fish species.
Daphnia, or Water Blook
move scroll. Daphny's body, 1-2 mm long, is concluded in a double transparent chitinic shell. The head is stretched into a keyless increase in the abdominal side. On the head there is one complex facet of eye and a simple eye in front of him. The first pair of the mustache is small, rowdowed. A mustache of the second pair is highly developed, doubletime (with their help, Daphnia floats). On the chest department there are five pairs of leaf-shaped legs, which are numerous pastry bristles. All together they form a filtration unit serving for filtering out of the water of small organic residues, single-celled algae and bacteria that feed Daphnes. At the base of the breast legs there are gill blades, in which gas exchange occurs. On the dorsal side of the body there is a barrel heart. No blood vessels. Through the transparent sink, a slightly curved tubing intestine with food, a heart, and under it a boding chamber, in which Daphny larvae develops.
- Subclass Malaacostraca (Higher Cracks). The structure is much more complicated than the lower cancers. Along with small plankton forms, there are relatively large types.
Higher crayfish are inhabitants of sea and fresh reservoirs. On land from this class only the lips and some cancers (palm cancer) live. Some types of higher crayfish serve as an object of fishery. In the seas of the Far East, the Golyan Pacific Crab is mined, the walled legs of which are used in food. Omar and Langust are mined in Western Europe. In addition to the cancer, they have a sanitary value, because Release reservoirs from animal corpses. Freshwater crabs and crabs in the countries of the East are intermediate owners for a pulmonary loser.
A typical representative of higher crayfish is a river cancer.
River Cancer lives in flowing fresh water reservoirs (rivers, streams), it feeds mainly vegetable food, as well as dead and alive animals. During the day, the river cancer is hiding in safe places: under stones, between the roots of coastal plants or in minks, which digs up with clamshes in cloth shores. Only with the onset of the night, he goes to look for food. On the wintering crayfish is hidden in their minks.
River Cancer structure and reproduction
External structure. The body of the river cancer outside is covered with a cuticle, impregnated with calcium carbonate, which gives it strength, so the cuticle is called a shell. The shell protects the body of the river cancer from damage and performs the function of the outer skeleton. In a young age, in the period of growth, river raks change the shell. This process was called molting. Over time, when river cancer reaches large sizes, it grows slowly and lines rarely.
The painting of the shell of a live river cancer depends on the color of the orstand the bottom on which it lives. It can be greenish-brown, light green, dark green and even almost black. Such painting has a protective nature and allows the cancer to become imperceptible. When caught crayfish, the destruction of a piece of chemicals that give the color of the shelter, but one of them is a red-colored pigment of astaxanthine - at 100 ° C it does not fall apart, which determines the red color of the boiled cancer.
The body of the river cancer is divided into three departments: head, chest and abdomen. From the dorsal side of the head and chest departments are covered with a single puppiest solid strong chitin shield, which carries a sharp spike in front of his sides in the recesses on movable stalks there are complex eyes, a pair of short and pair of long thin mustache. The latter are a modified first couple of limbs.
On the sides and below the mouth of the cancer, six pairs of limbs are located: the upper jaws, two pairs of the lower jaws and three pairs of the naughty. There are also five pairs of walking feet on the heads, there are claws on three front pairs. The first pair of walking feet is the largest, with the most well-developed claysters, which are protected and attack authorities. The mouth of the limbs along with the clashes hold food, grind it and direct in the mouth. The upper jaw is thick, served, powerful muscles are attached to it from the inside.
The abdomen consists of six segments. The limbs of the first and second segments in the male are modified (they are involved in copulation), the female has been reduced. On four segments there are two-way shouting zolics; The sixth pair of limbs is wide, lamellar, part of the tail fins (it plays an important role with the tail in the backward vice).
Movement of river cancer. River cancer can crawl and swim forward and backward. It crawls along the bottom of the reservoir with the help of breast-walled feet. Forward river cancer floats slowly, going through abdominal legs. To move back, it uses the tailflower. Running it and flexing the abdomen, river cancer makes a strong push and quickly floats back.
Digestive system It begins the mouth of the hole, then the food comes into the throat, short esophagus and stomach. The stomach is divided into two departments - chewing and comma. On the dorsal and side walls of the chewing department of the cuticle forms three powerful chitin-soaked chitin-free chewing plates with serial free, edges. In the CEDY DEPARTMENT, two plates with hairs act like a filter, through which only heavily crushed food. Next, food enters the middle intestine, which opens the ducts of a large digestive gland. Under the action of food allocated with iron, food is digested and absorbed through the walls of the middle intestine and the gland (it is also called the liver, but its secret splits not only fats, but also proteins and carbohydrates, i.e. functionally corresponds to the liver and pancreas of vertebrates). Unauthorized residues enter the render and are outwarded through the posterior hole on the tail blade.
Respiratory system. River racks breathe with the help of the gills. The gills are the cigarette growing of the chest limbs and the side walls of the body. They are located on the sides of the punching board inside a special gill cavity. Powding shield protects the gills from damage and rapid drying, so the cancer can live off the water for some time. But as soon as the gills get sick a little, the cancer dies.
Circulatory organs. Blood river cancer unlocked. The blood circulation is due to the work of the heart. The heart of the pentagonal shape is located on the dorsal side of the pitchflows under the shield. Blood vessels open from the heart, opening in the body cavity, where blood gives oxygen to fabrics and organs. Then the blood flows into the gills. The circulation of water in the gill cavity is ensured by the movement of a special process of the second pair of the lower jaws (it produces up to 200 mashauting movements in 1 min). Gas exchange takes place through the slim cuticle of the gills. Oxygen-enriched blood in the gumper-hearted channels is sent to the window-shaped bag, from there through special holes falls into the heart cavity. Cancer blood is colorless.
Options Pairies, have the form of round green glands, which are located at the base of the head and open out the opening at the base of the second pair of mustaches.
Nervous system It consists of a paired pumping unit (brain), incaploising conventionables and the abdominal nervous chain. From the brain, the nerves go to the toastic and eyes, from the first node of the abdominal nervous chain, or a sodlilt ganglia - to the oral organs, from the next pectoral and abdominal nodes of the chain - respectively, to the thoracic and abdominal limbs and internal organs.
Sense organs. Complex, or the facetful eyes in the river cancer are located in the front of the head on movable stalks. Each eye includes more than 3 thousand eyes, or facets separated from each other with thin pygment layers. The photosensitive part of each facet perceives only a narrow beam of rays perpendicular to its surface. An integer image is made up of a plurality of small partial images (as a mosaic image in art, so they say that arthropods have mosaic vision).
Cancer mustache serve as a touch and smell bodies. At the base of short mustows there is an equilibrium organ (stavocist, is mainly a segment of short detergents).
Reproduction and development. The river cancer has a sexual dimorphism. The male's first and second pair of abdominal legs are modified into a copulative organ. The female is the first pair of abdominal legs rudimentary, on the other four pairs of the abdominal legs, it shelters caviar (fertilized eggs) and young raffs, which for some time remain under the protection of the mother, clinging to their clasons for her abdominal limbs. So the female takes care of his offspring. Young raks are intensively growing and linked several times a year. The development of the river cancer is direct. Cracks multiply pretty quickly, despite the fact that they have a relatively few caviars: the female lays out from 60 to 150-200, rarely - up to 300 eggs.
The meaning of crustaceans
Daphnia, cyclops and other small crustaceans consume a large number of organic residues of dead small animals, bacteria and algae, thereby cleansing water. In turn, they represent an important source of food for larger invertebrate animals and fishes, as well as for some valuable planktonoid fish (for example, Citions). In pond fisheries and fish-tree plants, crustaceans are specifically bred in large basins, where they create favorable conditions for their continuous reproduction. Daphnia and other crustaceans are fed by young sturgeon, seven and other fish.
Many crustaceans have a commercial value. About 70% of the world's crustaceans are shrimp, they are also bred in ponds created on coastal lowlands and connected to the sea channel. Shrimps in ponds feed rice bran. Krill is underway - plankton marine crustaceans, forming large clusters and employees of food whales, lobs and fish. Food pasta, fat, firing flour are obtained from Krill. Less importance is fishery of lobs and crabs. In our country, Kamchatka crab is mined in the waters of Beringov, Okhotsk and the Japanese seas. River crayfish fishing is carried out in fresh reservoirs, mainly in Ukraine.
- CRUSTACEA class (crustacean)
On two nodclass - the lower crustaceans (Entomostraca) and the highest crustaceans (Malacostraca) - it turned out insolvent, since in the subclass of the lower crustaceans, the groups were not connected to each other. The subclass of the highest crustaceans has been preserved as a homogeneous group that occurs from one root.
Crack-shaped class (crustacea) is divided into 4 subclass: 1. Zabronoga (Branchiopoda); 2. MAXILLOPODA; 3. Cracked (Ostracoda); 4. Higher crustaceans (Malacoslraca).
Subclass. Zabronoga (Branchiopoda)
The most primitive crustaceans. The head is free, does not grow together: with breasts. Chest leaf legs, equipped with breathing blades (appendages), simultaneously perform motion, respiration and food to mouth. Abdominal limbs are absent from everyone, with the exception of a shield. Nervous staircase system. The subclass includes two major detachments.
Garron detachment (Anostraca)
Powding Shield - Carapaks - Suitable. Homonianly segmented body with a large number of segments (Zabronog 21 segments, not counting the heads). The head consists of two departments - the protocephalon (acron and antennal segment) and the tweeter (Mandibul segments, maxillars first and maxillars are second).
Breast legs are arranged very primitively and have thin-walled grown, filled with hemolymph (blood) and performing respiratory function. The blood system is represented by a long tubular heart with a pair of dues in each body segment. Nervous staircase system. Zabronogas are paired facetful eyes, but the unpaired nudinal eye is also preserved. Development with metamorphosis (Nauplius. Methanuplius).
This detachment includes conventional freshwater lats - gowns (Branchipus Stagnalis). Zhabronogs in a large number appear in spring water bodies. They are yellowish, with 11 pairs of breast legs and float back down. In salty lakes, Artemia Salina wraps capable of parthenogenetic reproduction (development) are common. Among them found polyploid races, with an increase in the chromosome set at 3, 4, 5 and 8 times.
Flylopoda detachment (PhylLopoda)
There is a punching shield, but it differs from different groups., The detachment includes three sub-trainers.
Substation 1. Schedule (Notostraca). The largest animals among the gowns, more than 5-6 cm long, covered with a wide flat headband, not closing only 10-15 rear legal segments with a long vocal, which ends Telson. The number of body segments is non-permanently (except 5 heads), it can reach 40 or more. On the front 12 segments (chest) there are one pair of sheet legs, and on the following several pairs (up to 5-6 pairs on one segment). A very primitive cross, close to the organization to Zhabronoga. Development with metamorphosis.
In standing spring reservoirs (often in large puddles) there are regular ships: Triops Cancriformis, Lepidurus APUS. Schedule is interesting to their sporadic appearance in small water bodies and rain puddles, often in large quantities. This is due to the belief that the shield falls allegedly from the sky with the rain. In fact, everything is explained by the fact that the wintering balls of the shoveline can carry a long period outside the water and transferred to the wind.
Ordinary shield (Triops Cancriformis) is a real living fossil, this species has not changed its organization from an early Mesozoic (Triass). Such a constancy of the type within 200 million can be explained by a very short term of its active life (3-4 weeks) and the emergency durability of the eggs.
The record 2. Konchostraki (Conchostraca). Representatives of it - ordinary bottom freshwater wraps, the length of the body of which ranges from 4 to 17 mm. Carapaks in the form of a bivalve greenish-brown sink, concluding the entire body of the lap, with its numerous (from 10 to 32) leaf-satellular legs. This includes large labels Limnadia, Cyzicus, etc.
The subverse 3. branchist (cladocera). In ponds, lakes and rivers you can always find representatives of this sub-train - small crustaceans, up to 2-3 mm (rarely 5 mm) lengths that make up a substantial part of freshwater plankton, which often appear in a huge amount. Representatives of the Daphny, or Water Bloch family are especially frequent: Daphnia Magna, Daphnia Pulex, SimoCephalus Vetulus, etc.
A duplex, flattened from the sides of the puppiest shield-karapaks - branchist covers the whole body, but the head is not covered. The abdomen of Daphnia, bend, also hiding under the shield. At the back end, the shield often ends with a sharp spike. In the daphnia on the head having the form of beak, except for a nudinal eye, there is also an unpaid facet of eye, consisting of a small number of ommatidis. Tireless eye is driven by special muscles.
The antennas are very short, and the antennas are turned into special locomotor organs, the two-ways are very developed, bisps are very developed. They are driven by strong muscles. Moving in the water, the branches produce strong cramped with antennas, and from each cramping their body bounces forward and up. The next moment the antenna is recorded for a new rowing movement, and the body of the lap somewhat lowers. For these peculiar movements of Daphnia and got the name "Water Bloch".
Breast limbs at branchist 4-6 pairs, and in many, in particular in Daphnia, they are a kind of filtering machine. These branching limbs are shortened, equipped with faster scallops and make rapid oscillatory movements. A constant current of water is created, from which small algae, bacteria and dadritis particles are filtered. Filtered food is compressed and moved to the mouth. With this device, Daphnya for 20-30 minutes filters such a number of foods that the entire intestine can fill. Some predatory branchist breast legs are segments and serve for grabbing.
On the dorsal side of the body, closer to the head, the heart is located as a small bag. It has one pair of acute and outlet in the front. Blood vessels are missing, and hemolymph circulates in the sinus of a mixture. The nervous system is very primitive and built as the gills, on the staircase type.
Of particular interest is the reproduction of branchist, in particular Daphny. They have an alternation of several parthenogenetic and one rolling generation. This type of reproduction is called heterogonia.
The development of branching eggs passes without metamorphosis (with the exception of one species). During the summer, only females that breed parthenogenetically and postponing "summer" eggs are usually found, which differ in that they have a double, diploid number chromosome.
Eggs are deposited into a special brood chamber, placed under the shell on the spinal side of the body, behind the heart.
Development direct. Young females of Daphnia are hatched from eggs.
With a deterioration of living conditions (decrease in water temperature, reducing the feeding of the reservoir, which is usually occurring in the fall) of Daphnesia begin to lay eggs having a haploid set of chromosomes. Of these or are formed (without fertilization), only small males, or eggs need fertilization. The eggs of the latter category are called resting. The males are 1.5-2.5 times less females, which they descend. Fertilized eggs differ from non-advocated larger sizes and a large number of yolks. First, fertilized eggs (two eggs) are placed in the brood chamber, and then a special saddle-ethipipium is formed from the part of the Daphnia shell. With a molting, Ethippium is separated from the maternal individual shell and plays the role of a protective shell around the egg. Since gas bubbles are formed in the wall of the zphippium, it does not sink and in the fall on the surface of the water, many epiphps appear on the surface. Etiphpiums are often equipped with hooks, hooks on long threads, which ensures the spread of Daphny on fresh reservoirs. Floating on the surface of water, the epipouls are hooking with hooks to the feathers of waterfowl and can be moved to the far reservoirs. Eggs enclosed in Etiphpiums winter and develop only in spring when the first generation of females come out of them.
Different branches have a change in body shape, depending on the living conditions. Often these changes are the right seasonal character, which is associated with periodic seasonal changes in conditions, and are called cyclomorphosis.
The branchist plays a large role in nutrition of freshwater fish, especially fry. Therefore, fish farms are extremely interested in enriching the fauna of branchist. Methods of artificial dampiness and enrichment of reservoirs have been developed.
Subclass. MAXILLOPODA
Sea and freshwater crustaceans. The number of segments of the chest department is constantly (usually 6, in some species 5 or 4). Breast legs have a motor or water function, do not participate in breathing. Abdominal legs are not.
Small crustaceans, 1-2 mm, rarely 10 mm long, without puppiest shield. The detachment includes about 2,000 species. Most of weary - planktonal forms. Running long antennas on the parties, they really hide them in the thickness of the water. In addition to soaring in plankton and jumping (cyclops) forms, among weakly, there are also bentos forms. Representatives of Cyclops and Diaptomus genera are common in fresh waters.
For weakly, the following features of the structure are characteristic. The antennas are strongly developed and play the role of cheerful from the cyclop or the apparatus for the harvest of other weary. Adaptations to the "steam" in the water sometimes cutting are expressed: the antennas and chest limbs in some marine weary are seated with long cider bristles directed to the parties, which greatly increases the surface of their body.
In males, the antennals are often turned into female holding bodies during mating. Other head limbs function largely as swimming legs.
Breast limbs are primitive, have a typical two-way character, but do not bear the gills. They have the importance of locomotor organs. They are caused by jump-shaped movements of weaklit.
The headband is formed by five spruce head segments and one breast. Free chest segments are usually 4, and abdominal 3-5, with a fork, or a car, at the end. There are no gowns, breathing occurs with the entire surface of the body. In this regard, the heart has no heart forms.
There is only an unpaid bait. Hence the name of cyclops (cyclops - one-eyed giants of Greek mythology).
Interesting biology of reproduction of weaklit. The sexual dimorphism, expressed mainly in the smaller sizes of males and in the structure of their antennal. After mating females, eggs are laying, gluing together with a special secret and forming one or two egg bags that remain attached to the sexual holes of the females before the larvae exit.
From the egg, the larvae of the nauplius, turning after molting in methaniplus, which is still three times, and the result is the third, compositive larva, after several links turning into an adult form.
Among the crustaceans, weakly occupy a special place by the huge value they have for the nutrition of many animals, primarily fish and whales. If branchwisters are a very essential part of freshwater plankton, then weakly are the most important part of the sea plankton, and many of them are common in fresh waters. For maritime plankton, representatives of the genus Calanus and others are characterized, which often appear, especially in the northern seas, in a huge amount, caused by this change in the color of water.
Detachment Usonogy (Cirripedia)
Sea Acorns (Balanus) often covered underwater objects in large quantities: stones, piles, mollusc shells. Outside, the lime sink of a truncated-conical shape, formed by individual, fragile with plates, is visible. A wider base of the sink grows to the substrate, and on the opposite side there is a lime cover from movable plates. The living balanca has a cap, and a beam of segic, musty, double-livery peppers in a constant rhythmic movement is turned out of it, which is also provided with food to mouth and respiration. This is the only external sign, indicating that the sealerious animal is before us.
Sea claritions (Lepas) differ from the marine acorns of the form and the fact that the lower (head) department forms a special, non-sink of the sink - leg. An animal is placed inside the sink on the dorsal side, legs up. Skin folds are adjacent to the walls of the shell - mantle.
At the young stages of development, the Uponogi is attached to the substrate by the head end, the antennals and special cement glands take part in this.
The belonging of the sucon-horned crustaceans is proved by the fact that the typical nudelius turns out of their eggs, which turns into metapaulus. The latter turns into a typical ciprice larva, which has a bivalve shell typical. It is called so because it looks like a Cypris seashell. This larva is attached with the help apprental to the substrate and turns into a semi-shaped shape of the sucion of cancer.
Usonogy Craki hermaphrodites, but some species have small additional males. Fertilization usually cross. The development of hermaphroditism among the sucked is associated with the transition to their sedentary lifestyle.
Cleancake subclass (Ostracoda)
These are very small wraps, most often with a size of 1-2 mm, in large numbers occurring in marine and fresh waters, predominantly bottom crawling forms, although there are floating ones among marine species - plankton. The number of birth and species is large: about 1500 species of shells are known in the seas and fresh waters.
A characteristic feature of the shells is a two-hand head shield, resembling the sink and completely hiding the entire body of the animal, unlike branchist, which remains a free head.
The organization of the shells is very simplified. Many have no bloodary system and gills, others have only hearts. The body of the shells is strongly shortened. The head carries five pairs of appendages, and the breast is only 1-2 pairs. Abdominal legs are absent, and the abdomen of some forms are equipped with a car. For most, only parthenogenetic females are known.
Cracked quickly and smoothly move in water, and the diving bodies serve as antennas and antennas. Cypris can also crawl through the substrate using antennas and breast legs.
The usual representative - Cypris - is found in almost any fresh reservoir; In the seas, Cypridina's crust is also common.
The subclass of the highest crustaceans (Malacoslraca)
The most highly organized from crustaceans, at the same time preserved some primitive features of the structure. The number of body segments is defined: four heads (not counting Acron), eight chest and six (or seven in thin-penetrating) abdominal, not counting Telson. Abdominal segments have limbs (6 pairs). Forks, or Furki, no, except for thin-pressed cancers. Segmentation is more heteronomous compared to representatives of other subclasses. Many forms are formed a headband, due to accession to the head segments of 1-2-3 breast segments. In some forms, a separate primitive primary head is preserved - Protocephalon. The blood system is developed, except the heart there are always blood vessels. The respiratory system in most species is represented by habra associated with breast or abdominal limbs.
The excretory organs of adult cancer are the antennal glands. Only the thinnesting glands are also present at the same time.
Development with metamorphosis or direct. When developing with metamorphosis, the stage of the Nauplius passes, with a rare exception, in egg shells. From the egg usually leaves Zoe or the larva of the misidal stage. The subclass includes several detachments.
Detachment Tonkone, or Nebalai (Leptostraca)
Nebalay is a very small group of small crustaceans (only 6 species are known). They are interesting because they have signs of the most primitive organization among higher crayfish and discover the similarities with zhabronogs. The presence of abdominal extremities and the antennal glands brings the nebali with the highest crustaceans. However, in contrast to all other higher crayfish, they have not 6, and 7 segments of the abdomen, anal segment of the abdomen ends with a fork. Other signs are characteristic of nonbali: 1) Two-screw shell, coating breasts and part of the abdomen; 2) eight pairs of identical two-way limbs, similar to the legs of the grocery; 3) the presence of two pairs of excretory glands at the same time in adults - antennal and rudimentary maxillary.
Nebalay is a very ancient group, and, apparently, they are closer to others to extinct, thencestrating primary crustaceans, which were ancestors of all modern crustacean class subclasses.
Misidacea detachment (mysidacea)
Misidals - a kind of group of predominantly sea crayfish, externally similar to small shrimp. Includes about 500 species leading the near-end or plankton lifestyle. Body sizes from 1-2 to 20 cm in bottom deep-water forms.
Miseids have stabbed eyes. The body of the misid is equipped with Carapaks, covering only 8 pairs of breastweight swimming legs. Abdominal with poorly developed limbs, long and free. Females have a brood chamber formed by the processes of the thoracic legs. Development direct.
Interesting the ability to purge a significant desalination, which gives them the opportunity to penetrate the seas in rivers and fresh lakes.
In Russia, the mealsids are common in the Caspian Sea and in the desired sites of the Black and Azov seas. They enter up the flow of large rivers and their tributaries, populate the reservoirs again created on them. Some kinds of misid are found only in fresh waters. Misidals are quite large, since they serve as the feed of many fishing fish.
Nefoda detachment (Isopoda)
The body of the equilibrium is flattened in the dorgentral direction. The headband consists of the head segments that have merged together, to which one or two breast segments joined. Headband is movably mounted with the rest of the chest segments. Carapaks is missing. Thoracic limbs are simolenty, walking type; Abdominal limbs are lamellar performing the gills function. In connection with the position of the gills on the babeline, the tubular heart is also located in the last two breast segments and in the trouser. The system of arterial blood vessels is developed.
The wet in connection with the ground lifestyle arise adapts to breathing with atmospheric air. Ordinary mocicians - no wonder so called - can only live in a wet environment, in sufficient dry air, many wets die quickly. The edges of the spinal panels in the wet lowered on the sides of the body and pressed to the substrate on which it sits. This supports sufficient humidity on the abdominal side of the body, where the modified gills are placed. Another kind of loccar is a coagured moc. (Armadillidium cinereum) - can live in dry places.
Many loccroids breathe gills that are protected from drying in a kind of gill cap (a modified pair of gill legs). The gills are moisturized with drip water captured by the sculpture of coverings or rear abdominal legs - urofodes. Some of the wets are capable of separating fluid through an anal hole, which helps to maintain the water covering the gills.
Finally, many wets develop so-called pseudotraches. In the front abdominal legs, piercing is formed, leading to the cavity, from which thin branching tubes filled with air are deposited. Unlike real fucking chitin, they do not form a spiral thickening.
Many types of wets are living in the soil, where they can harm cultural plants. . Some of them live in deserts, where they are very numerous and can benefit, participating in the cycle of organic matter and soil-educational processes. In Central Asia, the desert types of wets from the genus HEMILEPISTUS, sometimes occur in very large quantities.
Solid Blue Plaques (Amphipoda)
In terms of the organization, the booplasts are close to the equal. In the side of the headband is also formed by a jolly head and one breast segment. They also do not have a puppiest shield and breast limbs them are simoled. But at the same time, the booplasts are quite different from the equal. Their body is not flattened in the dorgentral, but in the lateral direction and is curved on the abdominal side. The gills are placed on breast legs. The females on 2-5 pairs of breast feet have special plates that together form a brood chamber. In connection with the position of the gills on the chest limbs, the tubular heart is also placed in the thoracic department. For swimming serve three pairs of front abdominal bivic limbs. The rear three pairs of abdominal legs jaming. Therefore, the Goypoch's detachment has a Latin name amphipoda, which means the differences.
Among the sea side, many lead the coastal lifestyle and even live in algae thrown into the pitfalls in the sands died in sand. Such, for example, sandy champs (Talitrus Saltator). In fresh waters, Gammarus Puex, living in small places of rivers and lakes.
A large number of peculiar, anywhere there are no more encountered types of boobs (about 240) lives in Lake Baikal. Boxes are in the nutrition of various fish.
Detachment Details Cancer (Decapoda)
The detachment of the tenth cancers unites about 8,500 species of the most highly organized crustaceans, often reaching very large sizes. Many of them are edible. Far Eastern Kamchatka crab, river cancer, some other crabs, shrimps serve as a fishery. Features of the organization's ten-sensitive cancers are known from the overall characteristics of the class of crustaceans.
All the tenthellies of cancers are stem, the three first breast segments are part of the pummaging, a puppiest shield - Carapaks - grips with all the breast segments, and does not cover them, like other crustaceans.
Most of the tensions are marine animals, but some live in fresh waters. Types of leading bentosny, bottom lifestyle (river cancer, crabs, hermit crayfish, etc.) are dominated. Very few (some crabs) adapted to life on land. In fresh waters, various types of river crayfish live, and a river crab occurs in the Crimea and Caucasus mountain rivers.
The detachment of the tenth cancers is divided into three suburbs: long-tailed cancers (Macrura), soft crayfish (Anomura) and short-eyed crayfish (Brachiura).
Long-tailed cancers have a long abdomen with well-developed abdominal legs. Long-tailed cancers, in turn, can be divided into crawling and floating.
First include river crayfish. The two most widespread fishing species of cancers live in Russia: widespread (Astacus Astacus) and narrow-step (A. leptodactylus). First meet; In the basin of rivers current in the Baltic Sea, the second - in rivers flowing into Black, Azov, Caspian Sea, in the Azov and Caspian seas and in the water bodies of Western Siberia. Usually these species are not found together. With joint habitat, narrowly cancer displaces more valuable broadcast. Large lobsters, the length of which can exceed 80 cm, and langusts (up to 75 cm), and langusti, and in different parts of the Atlantic Ocean and in different parts of the Atlantic Ocean are most valuable.
Floating long-tailed cancers are presented in the seas with many types of shrimp. Unlike bottom crustaceans - river cancer, lobster, etc., whose body is quite wide, - the body of shrimp is flattened with sides, which is explained by a floating lifestyle.
Shrimps are eaten, especially the population of seaside cities. In some countries, they serve as a subject of fishing.
Soft-tired crayfish, as a rule, benthosses living at various depths. The characteristic signs of soft-eyed crayfish are a softer, covered with less solid cover of abdomen, very often observed asymmetry of claw and abdomen, underdevelopment of some abdominal limbs.
This subdomain includes a biologically interesting group of cradle cancer. They stick their soft abdomen into suitable empty shells of bunthogged clams and drag them behind them. When the danger is approaching, the carbon cancer is hiding at all into the sink, covering the mouth to a more developed culse. Grown, Cancer Helf changes the sink to a larger one. Crayfish cancers often observed a curious symbiosis with actions. Some acts are settled on the shell occupied by hermit cancer. These acts acquire "mobility"., And the rains of hermites are better protected, having armed with shacting cells on the sink and almost inedible actinium. Also curious a symbiosis of craft cancer with sponges settled on their sinks.
The soft cancer includes some species that have external similarities with real crabs (wide and short headband and largely reduced abdomen). This is primarily a major fishing camchatic crab (Paralithodes Camtschathica), reaching 1.5 m in the removal of the limbs. He lives in the Far Eastern seas (Japanese, Okhotsk and Bering).
Finally, a very interesting crab-robber belongs to soft cancer, or a palm thief, reaching a length of 30 cm. It lives on the islands of the Pacific Ocean and is interesting as a shape adapted to life on land. It hides in non-flats lined with coconuts. Instead of the gills, he only has their rudiment, and the gill cavities on the sides of the puppiest shield turned into peculiar lungs. Palm thief is powered mainly by falling fruits of various palm trees, which he splits with its strong clamshes, and predates, attacking weakened animals.
Short-eyed cancers have a small, always a fitted abdomen. These include real crabs.
Crabs are typical bottom animals, well-adapted to life among stones, rocks, coral reefs in the journey strip of the sea, but there are forms living at large depths. Crabs are especially rich in the Far Eastern Sea. In the Black Sea, it is not very large common, with strong claws, stone crab (Cancer Pagurus), as well as other, smaller species.
Crab belongs the largest representative of crustaceans living at high depths in the Far Eastern seas - a giant Japanese crab (Macrocheria Kaempferi), reaching 3 m between the ends of the elongated medium breasts.
Crowdow phylogery
When studying crustaceans, we met many facts pointing to the possibility of their origin from Anneld. The most important of these facts are: 1) a parapodial type of structure of the most primitive two-track limbs; 2) the nature of the structure of the nervous system - the abdominal nerve chain or a more primitive staircase nervous system of zabronogs; 3) the type of structure of excretory organs originating from metanephridium polychaets; 4) tubular heart in the most primitive crustaceans, reminiscent of the spinal blood vessel annelide.
Different groups of crustaceans are already known to us from Paleozoic deposits, which indicates a very greater antiquity of their origin.
The most primitive group among modern crustaceans is undoubtedly a subclass of zhabronogs. Particularly important signs of grocery: 1) an indefinite and often large number of body segments; 2) the homomicity of their bodies segmentation; 3) primitive structure of breast limbs; 4) Ladder type of structure of the nervous system. The proximity is undoubtedly the origin between the gorgeous and branchist cancers, the latter are, however, a significantly more specialized group (antenna, brood chamber, generation change).
Glind, possessing some primitive signs, in other respects they have more progressive features. So, they have a head formed by five quite spilled segments, and the total number of body segments are always definitely and reduced to 14. The absence of some organs in weakly, such as facet and hearts, should be considered as the result of the secondary reduction.
The highest crustaceans undoubtedly have a more advanced organization than all other groups of crustaceans. However, they are not related to any of the groups of low-organized cancers, as they retained some very primitive signs, such as the presence of abdominal limbs that were fully reduced from other groups. Primary head - Protocephalon - also peculiar to many detachments of higher crayfish, whereas in other subclasses is less common.
Search
We can notify you about new articles,