Class Crustaceans. Crustaceans This is the name of the branch of zoology that studies crustaceans.

Class Crustaceans. Crustaceans This is the name of the branch of zoology that studies crustaceans.
Class Crustaceans. Crustaceans This is the name of the branch of zoology that studies crustaceans.
11.07.2024

Crustaceans are ancient aquatic animals with a complex body structure covered with a chitinous shell, with the exception of woodlice that live on land. They have up to 19 pairs of jointed legs that perform various functions: capturing and grinding food, movement, protection, mating, bearing young. These animals feed on worms, mollusks, lower crustaceans, fish, plants, and crayfish also eat dead prey - the corpses of fish, frogs and other animals, acting as orderlies of reservoirs, especially since they prefer very clean fresh water.

Lower crustaceans - daphnia and cyclops, representatives of zooplankton - serve as food for fish, their fry, and toothless whales. Many crustaceans (crabs, shrimp, lobsters, lobsters) are commercial or specially bred animals.

2 species of crustaceans are included in the Red Book of the USSR.

general characteristics

From a medical point of view, some species of planktonic crustaceans are of interest as intermediate hosts of helminths (Cyclops and Diaptomus).

Until recently, the Crustacean class was divided into two subclasses - lower and higher crustaceans. The subclass of lower crayfish included phyllopods, jawed crayfish and shell crayfish. It is now recognized that such a unification is impossible, since these groups of crayfish are different in origin.

In this section, the Crustacean class will be considered according to the old classification.

The body of crustaceans is divided into the cephalothorax and abdomen. The cephalothorax consists of segments of the head and chest, merging into a common, usually undivided body section. The abdomen is often dissected.

All crustaceans have 5 pairs of head limbs. The first 2 pairs are represented by segmented antennae; These are the so-called antennules and antennae. They carry the organs of touch, smell and balance. The next 3 pairs - oral limbs - are used to capture and grind food. These include a pair of upper jaws, or mandibles, and 2 pairs of lower jaws - maxilla. Each chest segment carries a pair of legs. These include: jaws, which are involved in holding food, and locomotor limbs (walking legs). The abdomen of higher crayfish also bears limbs - swimming legs. The lower ones don't have them.

Crustaceans are characterized by a bibranched limb structure. They distinguish between the base, external (dorsal) and internal (ventral) branches. This structure of the limbs and the presence of gill outgrowths on them confirms the origin of crustaceans from polychaete annelids with bibranched parapodia.

In connection with the evolution in the aquatic environment, crustaceans have developed organs of aquatic respiration - gills. They often appear as outgrowths on the limbs. Oxygen is delivered by blood from the gills to the tissues. Lower crayfish have colorless blood called hemolymph. Higher crayfish have real blood containing pigments that bind oxygen. The blood pigment of crayfish - hemocyanin - contains copper atoms and gives the blood a blue color.

The excretory organs are one or two pairs of modified metanephridia. The first pair is localized in the anterior part of the cephalothorax; its duct opens at the base of the antennae (antennary glands). The duct of the second pair opens at the base of the maxillae (maxillary glands).

Crustaceans, with rare exceptions, are dioecious. They usually develop through metamorphosis. A nauplius larva emerges from the egg with an unsegmented body, 3 pairs of limbs and one unpaired eye.

  • Subclass Entomostraca (lower crayfish).

    Lower crayfish live in both fresh waters and seas. They are important in the biosphere, being an essential part of the diet of many fish and cetaceans. The most important are copepods (Copepoda), which serve as intermediate hosts of human helminths (diphyllobothriids and guinea worms). They are found everywhere in ponds, lakes and other standing bodies of water, inhabiting the water column.

general characteristics

The body of the crustacean is divided into segments. The complex head bears one eye, two pairs of antennae, mouthparts, plus a pair of legs-jaws. One pair of antennas is much longer than the other. This pair of antennas is highly developed, their main function is movement. They also often serve to hold the female by the male during mating. Chest of 5 segments, pectoral legs with swimming setae. Abdomen of 4 segments, at the end - a fork. At the base of the female's abdomen there are 1 or 2 egg sacs in which eggs develop. Nauplii larvae emerge from the eggs. The hatched nauplii look completely different from adult crustaceans. Development is accompanied by metamorphosis. Copepods feed on organic debris, tiny aquatic organisms: algae, ciliates, etc. They live in reservoirs all year round.

The most common genus is Diaptomus.

Diaptomus live in the open part of water bodies. The size of the crustacean is up to 5 mm. The body is covered with a rather hard shell, which makes it reluctant to be eaten by fish. The color depends on the nutrient base of the reservoir. Diaptomuses have 11 pairs of limbs. The antennules are single-branched, the antennae and legs of the thoracic segments are biramous. The antennules reach especially great lengths; they are longer than the body. Scattering them widely, diaptomuses float in the water, the thoracic limbs cause the jerky movements of the crustaceans. The oral limbs are in constant oscillatory motion and drive particles suspended in water towards the mouth opening. In Diaptomus, both sexes take part in reproduction. Diaptomus females, unlike Cyclops females, have only one egg sac.

Species of the genus Cyclops (cyclops)

inhabit mainly coastal zones of water bodies. Their antennae are shorter than those of diaptomus and participate, along with the thoracic legs, in irregular movements. The color of cyclops depends on the type and color of the food they eat (gray, green, yellow, red, brown). Their size reaches 1-5.5 mm. Both sexes take part in reproduction. The female carries fertilized eggs in egg sacs (Cyclops have two), attached at the base of the abdomen.

In terms of their biochemical composition, copepods are in the top ten high-protein foods. In aquarium farming, “Cyclops” is most often used to feed grown juveniles and small-sized fish species.

Daphnia, or water fleas

move spasmodically. The body of daphnia, 1-2 mm long, is enclosed in a bivalve transparent chitinous shell. The head is extended into a beak-like outgrowth directed towards the ventral side. On the head there is one complex compound eye and in front of it a simple ocellus. The first pair of antennae is small and rod-shaped. The antennae of the second pair are highly developed, bibranched (with their help, daphnia swims). On the thoracic region there are five pairs of leaf-shaped legs, on which there are numerous feathery bristles. Together they form a filtration apparatus that serves to filter small organic residues, unicellular algae and bacteria from the water that daphnia feed on. At the base of the thoracic legs there are gill lobes in which gas exchange occurs. On the dorsal side of the body there is a barrel-shaped heart. There are no blood vessels. Through the transparent shell, the slightly curved tube-shaped intestine with food, the heart, and below it the brood chamber in which daphnia larvae develop are clearly visible.

  • Subclass Malacostraca (higher crayfish). The structure is much more complex than that of lower crayfish. Along with small planktonic forms, relatively large species are found.

    Higher crayfish are inhabitants of marine and fresh water bodies. Only woodlice and some crayfish (palm crayfish) live on land from this class. Some species of higher crayfish serve as commercial fisheries. In the seas of the Far East, a gigantic Pacific crab is caught, whose walking legs are used for food. In Western Europe, lobster and lobster are caught. In addition, crayfish have sanitary significance, because... clear water bodies of animal corpses. Freshwater crayfish and crabs in Eastern countries are intermediate hosts for the pulmonary fluke.

    A typical representative of higher crayfish is the river crayfish.

Crayfish live in flowing fresh water bodies (rivers, streams), feed mainly on plant foods, as well as dead and living animals. During the day, the crayfish hides in safe places: under stones, between the roots of coastal plants, or in burrows that it digs with its claws in steep banks. Only when night falls does he come out to look for food. For the winter, crayfish hide in their burrows.

Structure and reproduction of crayfish

External structure. The body of the crayfish is covered on the outside with a cuticle impregnated with calcium carbonate, which gives it strength, which is why the cuticle is called the shell. The shell protects the body of the crayfish from damage and serves as an exoskeleton. At a young age, during the growth period, crayfish change their shell. This process is called molting. Over time, when the crayfish reaches a large size, it grows slowly and sheds rarely.

The color of the shell of a living crayfish depends on the color of the muddy bottom on which it lives. It can be greenish-brown, light green, dark green and even almost black. This coloring is protective and allows the cancer to become invisible. When caught crayfish are boiled, some of the chemical substances that give color to the shell are destroyed, but one of them - the red pigment astaxanthin - does not decompose at 100 °C, which determines the red color of the boiled crayfish.

The crayfish's body is divided into three sections: head, chest and abdomen. On the dorsal side, the head and thoracic sections are covered with a single cephalothoracic solid, strong chitinous shield, which bears a sharp spike in front; on its sides, in recesses on movable stalks, there are compound eyes, a pair of short and a pair of long thin antennae. The latter are a modified first pair of limbs.

On the sides and below the mouth opening of the crayfish there are six pairs of limbs: the upper jaws, two pairs of lower jaws and three pairs of maxillae. There are also five pairs of walking legs on the cephalothorax; the three front pairs have claws. The first pair of walking legs is the largest, with the most well-developed claws, which are organs of defense and attack. The oral limbs, together with the claws, hold food, crush it and direct it into the mouth. The upper jaw is thick, jagged, and powerful muscles are attached to it from the inside.

The abdomen consists of six segments. The limbs of the first and second segments are modified in the male (they participate in copulation), while in the female they are reduced. On four segments there are two-branched segmented toes; the sixth pair of limbs are wide, lamellar, part of the caudal fin (it, together with the caudal blade, plays an important role when swimming backwards).

Movement of crayfish. Crayfish can crawl and swim forward and backward. It crawls along the bottom of the reservoir with the help of its pectoral walking legs. The crayfish swims forward slowly, moving its abdominal legs. To move backwards, it uses the caudal fin. By straightening it and tucking its abdomen, the crayfish makes a strong push and quickly swims back.

Digestive system begins with the mouth opening, then food enters the pharynx, short esophagus and stomach. The stomach is divided into two sections - chewing and filtration. On the dorsal and lateral walls of the chewing section, the cuticle forms three powerful chitinous chewing plates impregnated with lime with serrated free edges. In the filtering section, two plates with hairs act like a filter through which only highly crushed food passes. Next, the food enters the midgut, where the ducts of the large digestive gland open. Under the influence of digestive enzymes secreted by the gland, food is digested and absorbed through the walls of the midgut and gland (it is also called the liver, but its secretion breaks down not only fats, but also proteins and carbohydrates, i.e. functionally corresponds to the liver and pancreas of vertebrates). Undigested remains enter the hindgut and are excreted through the anus on the tail blade.

Respiratory system. Crayfish breathe using gills. Gills are feathery outgrowths of the thoracic limbs and lateral walls of the body. They are located on the sides of the cephalothorax shield inside a special gill cavity. The cephalothorax shield protects the gills from damage and rapid drying, so the crayfish can live out of water for some time. But as soon as the gills dry out a little, the cancer dies.

Circulatory organs. The circulatory system of crayfish is not closed. Blood circulation occurs due to the work of the heart. The heart is pentagonal in shape, located on the dorsal side of the cephalothorax under the shield. Blood vessels extend from the heart and open into the body cavity, where the blood gives oxygen to tissues and organs. The blood then 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 lower jaws (it produces up to 200 flapping movements per minute). Gas exchange occurs through the thin cuticle of the gills. Oxygen-enriched blood is directed through the gill-cardiac canals into the pericardial sac, from where it enters the heart cavity through special openings. Cancer blood is colorless.

Excretory organs paired, they look like round green glands, which are located at the base of the head and open outward with a hole at the base of the second pair of antennae.

Nervous system consists of a paired suprapharyngeal node (brain), peripharyngeal connectives and a ventral nerve cord. From the brain, nerves go to the antennae and eyes, from the first node of the abdominal nerve chain, or subpharyngeal ganglion, to the oral organs, from the next thoracic and abdominal nodes of the chain, respectively, to the thoracic and abdominal limbs and internal organs.

Sense organs. The compound or compound eyes of crayfish are located in the front of the head on movable stalks. Each eye includes more than 3 thousand ocelli, or facets, separated from each other by thin layers of pigment. The photosensitive part of each facet perceives only a narrow beam of rays perpendicular to its surface. The whole image is made up of many small partial images (like a mosaic image in art, which is why arthropods are said to have mosaic vision).

The crayfish's antennae serve as organs of touch and smell. At the base of the short antennae there is an organ of equilibrium (statocyst, located in the main segment of the short antennae).

Reproduction and development. Crayfish have developed sexual dimorphism. In the male, the first and second pairs of abdominal legs are modified into a copulatory organ. In the female, the first pair of abdominal legs is rudimentary; on the remaining four pairs of abdominal legs, she bears eggs (fertilized eggs) and young crustaceans, which remain under the protection of the mother for some time, clinging to her abdominal limbs with their claws. This is how the female takes care of her offspring. Young crayfish grow rapidly and molt several times a year. Development in crayfish is direct. Crayfish reproduce quite quickly, despite the fact that they have relatively few eggs: the female lays from 60 to 150-200, rarely up to 300 eggs.

The meaning of crustaceans

Daphnia, cyclops and other small crustaceans consume large amounts of organic remains of dead small animals, bacteria and algae, thereby purifying the water. In turn, they represent an important food source for larger invertebrate animals and juvenile fish, as well as for some valuable planktivorous fish (for example, whitefish). In pond fish farms and fish hatcheries, crustaceans are specially bred in large pools, where favorable conditions are created for their continuous reproduction. Daphnia and other crustaceans are fed to juvenile sturgeon, stellate sturgeon and other fish.

Many crustaceans are of commercial importance. About 70% of the world's crustacean fisheries are shrimp, and they are also bred in ponds created in the coastal lowlands and connected to the sea by a canal. Shrimp in ponds are fed with rice bran. There is a fishery for krill - planktonic marine crustaceans that form large aggregations and serve as food for whales, pinnipeds and fish. Food pastes, fat, and feed meal are obtained from krill. The fishing for lobsters and crabs is of less importance. In our country, Kamchatka crab is harvested in the waters of the Bering, Okhotsk and Japan seas. Commercial fishing for crayfish is carried out in fresh water bodies, mainly in Ukraine.

  • Class Crustacea (crustaceans)

Many crustaceans are consumed by humans; shrimp are especially consumed. Crustaceans such as copepods and krill may have the greatest biomass of any animal on the planet. They are the most important link in food chains.

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    Subtitles

Structure and physiology

External structure

Body measurements

Segmentation and limbs

Initially, the body of crustaceans includes 3 sections: head, thoracic and abdominal. In some primitive species, the thoracic and abdominal regions are segmented almost homonomically (that is, they consist of almost identical segments). The number of body segments varies greatly: from 5-8 to 50. It is currently believed that during the evolution of crustaceans, like other arthropods, there was a decrease in the number of segments. In higher crayfish, the number of segments is constant: acron, 4 head segments, 8 thoracic segments and 6 abdominal segments.

Limbs

The body segments bear a pair of two-branched limbs. In a typical case, the limb of a crustacean consists of a basal part - protopodite, carrying two branches: outer - exopodite and internal - endopodite. The protopodite includes two segments: coxopodite, usually bearing a gill appendage, and basipodite, to which the exopodite and endopodite are attached. The exopodite is often reduced, and the limb takes on a single-branched structure. Primarily, the limbs of crustaceans performed several functions: motor, respiratory, and also auxiliary for feeding, but in the majority there is morphofunctional differentiation of the limbs.

Head

The head consists of a head blade - acron and four segments. The head bears acron appendages - the first antennae ( antennules) and the limbs of the next four segments: antennas second, mandibles, or mandibles(upper jaws) and two pairs maxillus(mandibles). Sometimes the first pair of mandibles is called maxillulae, and the maxillae - the second. The antennules are usually single-branched and homologous to the palps of polychaetes. The exopodite of the second antenna is called scaphocerite. The antennae perform the function of sensory organs, sometimes movement, the remaining head appendages are involved in capturing and grinding food. Mandibles play a major role in grinding food. In the larva - nauplius - the mandible is a typical two-branched limb with a chewing process. Adults rarely have a similar form of mandible; usually both branches are reduced, and the protopodite with a chewing process forms the upper jaw, to which the muscles are attached. The maxillae usually have the appearance of delicate leaf-like stalks with chewing processes on the protopodite and somewhat reduced rami.

The head can be either one piece ( syncephalon), and divided into two articulated sections: protocephalon, which is formed by the fusion of the acron and the first head segment and carries the first two pairs of antennas, and gnatocephalon, formed by the fusion of the last three head segments and bearing mandibles and maxillae. The last option occurs in the orders: branchiopods, mysids, euphausians, decapods, stomatopods. The oral opening is covered in front by an unpaired fold of cuticle - upper lip. Often in higher crayfish (such as crayfish), the gnatocephalon fuses with the thoracic region, forming jawchest (gnathothorax), covered with a dorsal shell - carapace. The body of higher crayfish is divided into the following sections: head - protocephalon (acron and 1 segment), maxillary thorax - gnathothorax (3 cephalic and 8 thoracic segments) and abdomen (6 segments and telson). In other cases, there is a fusion of the entire head, not divided into protocephalon and gnathothocephalon, with one or more thoracic segments. This is how it is formed cephalothorax, followed by the thorax and abdomen. In some crustaceans (for example, cladocerans), the head is extended into a downward-pointing beak - rostrum.

Thoracic region

The thoracic region, like the abdominal region, can have a different number of segments. Some crayfish, such as branchiopods, have multifunctional abdominal limbs, while others have a separation of functions. So, crayfish have 3 first pairs of thoracic legs - two-branched maxillary, serving for holding and straining food, the next 3 are single-branched walking and at the same time grasping, with a claw at the end, but all pectoral legs at the base bear gills.

Abdominal

The abdominal region consists of several segments and a telson; as a rule, he is limbless. Only in higher crayfishes are bipartite limbs located on the abdomen, performing various functions: in shrimps - swimming, in stomatopods - respiratory, in male crayfish the first 2 pairs are modified into copulatory organs, and in females the first pair is reduced, the remaining abdominal legs are intended for bearing young. In most decapods, the last pair of abdominal legs is plate-shaped ( uropods) and together with the telson forms a five-lobed “fin”.

Crustaceans lacking abdominal limbs usually have fork(furca), formed by articulated appendages of the telson. Only the crustacean has both a fork and abdominal legs. Nebalia. In crabs, the abdominal region is reduced.

Veils

Like other arthropods, crustaceans have a durable chitinous exoskeleton (cuticle). The cuticle consists of several layers, its peripheral layers are impregnated with lime, and the internal ones consist mainly of soft and elastic chitin. In small lower forms the skeleton is soft and transparent. In addition, the chitinous cuticle contains various pigments that give the animal a protective coloring. Pigments are also contained in the hypodermis. Some crustaceans are able to change color by changing the distribution of pigment grains in the cells (if the pigment is concentrated in the center of the cell, the color disappears, but if the pigment is evenly distributed in the cell, the color will appear in the integument). This process is regulated by neurohumoral factors.

The function of the exoskeleton is not limited to protecting the animal; various muscles are also attached to the cuticle. Often, for their attachment, there are special processes in the form of ridges and crossbars on the underside of the cuticle.

The mobility of such parts of the crustacean body is ensured by special soft membranes located between the fused parts of the body, segments or segments of the limbs and appendages. The compacted areas of the segments on the dorsal side are called tergites, and on the abdominal - sternites. The carapace already mentioned above is a special fold of the integument. It may be shaped like a shield, a bivalve shell, or a half-cylinder. The carapace can cover various sections: the head, chest (crayfish, crayfish) or the entire body (daphnia, shell crayfish); in higher crayfish, its lateral parts cover the gills.

Internal structure

Musculature

The musculature of crustaceans is represented by striated muscle tissue, as in all arthropods. They do not have a single skin-muscular sac, and the muscles are represented by separate, more or less large bundles. Typically, one end of the muscle is attached to the wall of one segment of the body or limb, the other - to the wall of another segment. Shell crustaceans with a bivalve shell have a special closing muscle that runs across the body and connects the two shell valves.

Digestive system

The digestive system of crustaceans is well developed, looking like a straight or slightly bent tube. Like all arthropods, it consists of an ectodermal foregut, an endodermal midgut, and an ectodermal hindgut.

The foregut is represented by the esophagus and stomach and is lined with a chitinous cuticle. The stomach can be divided into chewing (cardiac), in which food is crushed using chewing plates - jagged, lime-soaked thickenings of the cuticle on the walls of the stomach, and pyloric, in which food is filtered using thin cuticular processes that form something like a filter, sections (for example, in crayfish).

The ducts of paired hepatic appendages, which are lateral protrusions of the wall, flow into the midgut. When abundantly developed, these appendages are called the liver. The liver of crustaceans not only secretes digestive enzymes, but also absorbs digested food. Its enzymes act on fats, proteins and carbohydrates. Thus, functionally, the liver of crustaceans corresponds to the liver and pancreas of vertebrates. The liver carries out both intracellular and intracellular digestion. There is an inverse relationship between the sizes of the midgut and liver. In copepods, the midgut has the appearance of a simple tube and is devoid of hepatic protrusions. In its rudimentary state, the liver is present in some cladocerans; in amphipods and isopods, the liver looks like two pairs of long tubular sacs.

The hindgut is rectal, lined with chitinous cuticle. The anus opens on the ventral side of the telson (anal lobe). During molting in crustaceans, in addition to the outer chitinous cover, the lining of the anterior and posterior sections is also shed. Until the new covers harden, the cancer does not feed.

Respiratory system

Most crustaceans breathe through skin gills, which are feathery or lamellar outgrowths - epipodites, extending from the protopodites of the legs. As a rule, they are located on the thoracic limbs; only in stomatopods and isopods are the abdominal legs completely transformed into gills. In decapod crustaceans, gills also form on the body wall in the gill cavities under the carapace, gradually moving from protopodites to the body wall. In this case, the gills in decapods are arranged in three longitudinal rows: in the first row, the gills retain their primary location on the protopodites of the body, in the second they sit at the junction of the protopodites with the body, in the third they have already completely moved to the side wall of the body. The body cavity continues in the gills, into which the hemolymph enters. Gas exchange occurs through the very delicate cuticle of the gills.

The flow of water in the gills is carried out as follows. Water enters the gill cavities from one end of the body through a gap between the carapace and the body, and is pushed out from the other, and the direction of the water flow can change. The conduction of water is also facilitated by the movement of special processes of the second pair of maxillae, making up to 200 flapping movements per minute.

Many small crustaceans with a thin carapace do not have gills, and breathing occurs through the entire surface of the body. Land crustaceans have special adaptations for breathing atmospheric oxygen, for example, pseudotrachea (deep invaginations) on the abdominal legs of woodlice. The limb cavity is filled with hemolymph, which washes the invaginations and carries out gas exchange. Land crabs breathe oxygen dissolved in water, which covers the membranes of the gill cavity with a thin film and is protected from evaporation by the carapace. However, land crustaceans still need high air humidity to breathe.

Circulatory system

Like all arthropods, crustaceans have a mixed body cavity (mixocoel) and an open circulatory system (that is, hemolymph flows through the vessels and sinuses of the myxocoel). The heart is located above the intestines, on the dorsal side of the body and is located near the respiratory organs (if gills are only on the thoracic legs, the heart is in the thoracic region, etc.). In the most primitive crustaceans, the heart is metameric, multi-chambered, and is represented by a long tube running along the entire body (some branchiopods) and having a pair of ostia (holes) in each segment (chamber). In other crustaceans, the heart is shortened: in water fleas, the heart is shortened to the extent of a barrel-shaped sac with one pair of awns; in decapods, the heart is a small sac with three pairs of awns. Among the higher crayfish there are representatives with both long and short hearts.

The heart of crustaceans is in pericardial sinus mixocoel. From there, the hemolymph enters the heart through the ostia. When the chambers of the heart contract, the valves of the ostia close, the valves of the cardiac chambers open, and hemolymph is expelled into the arteries: anterior and posterior. From there, the hemolymph flows into the spaces between the organs, where it gives off oxygen and is saturated with carbon dioxide. It performs the function of gas exchange due to the presence of respiratory pigments - hemocyanin (in higher crayfish) or hemoglobin (in copepods, barnacles, barnacles and branchial crayfish), which bind oxygen. The hemolymph partially washes the kidneys, where it is freed from metabolic products. Next, it is collected in the system of venous vessels, delivered to the gill system of capillaries, gives off carbon dioxide and is saturated with oxygen. Then the efferent branchial vessels deliver it to the pericardial sinus.

The degree of development of the circulatory system is related to the development of the respiratory system. In small crustaceans that carry out gas exchange through the body wall, only the heart remains of the circulatory system or it disappears completely.

Excretory system

The excretory system of crustaceans is represented by kidneys, which are modified coelomoducts. Each kidney consists of a coelomic sac and a convoluted excretory tubule that can expand to form the bladder. Depending on the location where the excretory pores open, there are two types of buds: antennal(first pair; excretory pores open at the base of the second antennae) and maxillary(second pair; at the base of the second pair of maxillae). Higher crayfish in adulthood have only antennal buds, all others have only maxillary buds. Only the already mentioned crustacean has both pairs of kidneys. Nebalia from the group of higher crayfish, as well as in seashell crustaceans. The remaining crustaceans have only one of two pairs of kidneys, and in the process of ontogenesis they change: if in the larval state the maxillary glands function, then in the adult the antennal glands function. Apparently, crustaceans originally had 2 pairs of kidneys, like Nebalia, but during subsequent evolution they retained only one.

Nervous system

The nervous system of crustaceans, like all arthropods, is represented by paired supra-pharyngeal ganglia, a nerve ring and a ventral nerve cord. Primitive branchial crayfish have a scalene-type nervous system: paired ganglia in segments are widely spaced and connected by commissures. In most crustaceans, the abdominal trunks have become closer, the right and left ganglia have merged, the commissures have disappeared, and only the duality of the longitudinal jumpers between the ganglia of adjacent segments indicates the paired origin of the abdominal nerve cord. Like most arthropods, crustaceans show a tendency to oligomerize (fusion) ganglia from different segments, which distinguishes the abdominal nerve cord of arthropods from that of annelids. Thus, crayfish, whose body consists of 18 segments, has only 12 nerve ganglia.

Brain crustaceans are represented by paired lobes protocerebrum(innervation of the acron and eyes) with mushroom bodies And deutocerebrum(innervation of the antennules). Usually, the ganglia of the segment that moves forward and carries the second pair of antennae merge with the brain. In this case, the third department is separated - tritocerebrum(innervation of the antennae), in other crustaceans the antennae are controlled by the peripharyngeal ring.

Crustaceans have a well-developed sympathetic nervous system, mainly innervating the intestines. It consists of a cerebral section and an unpaired sympathetic nerve, along which there are several ganglia.

The nervous system of crustaceans is closely related to the endocrine system. The ganglia of crayfish include neurosecretory cells that secrete hormones that enter the hemolymph. These hormones influence metabolic processes, molting and development. Neurosecretory cells are located in various parts of the protocerebrum, tritocerebrum and ganglia of the ventral nerve cord. In some crustaceans, hormones from the neurosecretory cells of the optic nerves enter a special sinus gland and from there into the hemolymph. They are responsible for the mechanism described above for changing body color.

Sense organs

Organs of vision

A simple ocellus is a pigment cup into which the visual cells face. It is covered with a transparent cuticle that forms the lens. Light first passes through the lens, visual cells, and only then to their light-sensitive ends. These eyes are called inverted(that is, converted). Simple ocelli are collected in groups of 2-4 and form an unpaired nauplius (nauplial) eyes, characteristic of the larvae of crustaceans - nauplius. In adult nauplii, the eye is located between the bases of the antennae.

Compounded eyes consist of simple ocelli - ommatidia. Each simple eye is a cone-shaped glass, bounded by pigment cells and covered on top with a hexagonal cornea. The light-refracting part of the ommatidium consists of cells crystal cone, and photosensitive - retinal cells, at the point of contact of which a photosensitive rod is formed - rhabdom. In crustaceans with compound eyes, there is mosaic vision, that is, the overall visual perception consists of parts perceived by individual ommatidia. Compound eyes often sit on special movable outgrowths of the head - stalks.

In some crayfish, visual perception of certain light stimuli is necessary to trigger the mechanism described above for changing body color.

Organs of balance

Some crustaceans have balance organs - statocysts. In crayfish they are located at the base of the antennules. During the molting period, the lining of the statocyst changes, and the animal loses coordination of movement. Statocysts are characteristic of decapods and some other higher crustaceans.

Other senses

The organs of touch and smell in crustaceans are numerous sensilla and tactile hairs, mainly located on the antennae, limbs and furcula. The sense of touch is confined only to those areas of the integument where sensitive hairs are located. At the base of such hairs, under the hypodermal epithelium, there are bipolar neurons. Hairs with a particularly permeable cuticle, localized on the antennae, are organs of smell.

Reproductive system

Sometimes in males, the antennae or antennules act as grasping organs, and in crayfish, 1-2 pairs of abdominal legs function as copulatory organs. Gonads in primitive forms, genital ducts and openings are paired. Much more often, the gonads are completely or partially fused. The walls of the oviducts secrete a dense shell around the eggs. In some cases, females have seminal receptacles. In this case, fertilization occurs when the female lays eggs and sprays them with sperm from the openings of the spermatheca. In some crayfish, spermatophore fertilization occurs; When mating, males of these species glue spermatophores to the female’s body or insert them into her genital opening.

Crustaceans vary widely in the shape and size of sperm. Thus, in some small shell crustaceans, the length of sperm is 6 mm, which is 10 times longer than the animal itself. At Galatea ( Galathea) and higher crayfish, the sperm is similar to an hourglass. During fertilization, the sperm is attached to the egg with processes, then the tail part of the sperm, absorbing moisture, swells and explodes, and the head end with the nucleus sticks into the egg.

Most crayfish are characterized by caring for their offspring, although some of them simply throw eggs into the water column. Often, females carry eggs glued to the genital openings in the form of egg sacs (characteristic of copepods) or long threads. Decapods glue eggs to the limbs of the abdomen. In percarids, shieldfishes, branchiopods and many isopods, the carapace and thoracic legs form brood pouch (marsupium). Most thin-shelled and krill crustaceans carry their eggs between their thoracic legs. Female carp eaters do not carry eggs, but lay them in rows on stones and other objects.

The fertility of crayfish varies.

The eggs of some crayfish (scuttlefish and branchiopods) are highly resistant: they easily tolerate drying out, freezing and are carried by the wind.

Life cycle

Embryonic development

The nature of crushing of crustaceans depends on the amount of yolk in the eggs. When there is little yolk in the egg (for example, some copepods), crushing occurs similar to the crushing of annelids: it is complete, uneven, determinate, with teloblastic laying of the mesoderm (that is, from a cell - teloblast).

In most crayfish, the eggs are rich in yolk, and crushing becomes partial and superficial. During several divisions of the nucleus without cell division, daughter nuclei are formed that go to the periphery and are located there in one layer (therefore, the fragmentation of crustaceans is called superficial). Next, a section of cytoplasm separates around each nucleus, and a small cell is formed; the central mass of the yolk remains undivided. This stage is similar to a blastula with a blastocoel filled with yolk. Then part of the blastula cells on the future abdominal side goes under the outer layer, forming a multicellular plate - germ band. Its outer layer is formed by ectoderm, the deeper ones are mesoderm, the deepest layer, adjacent to the yolk, is endoderm.

Further development of the embryo occurs mainly due to the germ band. It begins to segment, and from its most anterior and powerful section, paired cephalic ganglia appear, due to which complex eyes arise. Behind it, the rudiments of the acron, antennal and mandibular segments are formed. Sometimes the mesoderm is laid down in the form of paired coelomic sacs, like in annelids, which are subsequently destroyed: their cells go to build mesodermal organs (muscles, heart, etc.), and the cavities merge with the remains of the primary body cavity. This is how the mixocoel, or mixed body cavity, is formed. In some cases, the mesoderm loses distinct segmentation, and a pronounced coelom is not formed at all.

Postembryonic development

Crustacean larvae

In higher crustaceans, the metanauplius stage is followed by a special larval stage - zoea(the larva received this name when scientists considered it a separate species). This larva has developed cephalic and prothoracic limbs, has the rudiments of the remaining thoracic legs, and a formed abdomen with the last pair of legs. In addition, zoea has compound eyes. The zoea then develops into mysid larva with formed thoracic legs and the rudiments of all abdominal limbs. After this, the mysid larva molts and transforms into an adult animal.

Some higher crayfish have differences from the life cycle described above. Thus, in many crabs a zoea immediately emerges from the egg, but in crayfish the development is direct: a young crustacean with a full complement of segments and limbs emerges from the egg, then it grows and molts, turning into an adult.

Finally, different groups of crustaceans may have distinct larval stages.

Shedding

Molting in crustaceans is most well studied using the example of higher crayfish. It is accompanied by both morphological and physiological changes.

Before molting, a number of organic (lipids, proteins, vitamins, carbohydrates, etc.) and mineral compounds accumulate in the tissues and hemolymph of the animal. Some of it comes from the old cuticle. Oxygen consumption increases, the intensity of metabolic processes increases.

At the same time, hypodermal cells begin to secrete a new cuticle using substances from the hemolymph and tissues. The new cuticle gradually thickens, maintaining, however, flexibility and elasticity. Finally, the old cuticular cover bursts, the animal climbs out of it, leaving an empty cover - exuvium. A crayfish that has molted quickly increases in size, but not due to the proliferation of tissues, but due to the accumulation of water in them. Due to cell division, tissue volume increases only between molts. Some time after the exuvium is shed, mineral salts are deposited in the new cuticle, and it quickly hardens.

The molting process is regulated by the hormonal system. An important role in it is played by neurosecretory cells associated with the sinus gland mentioned above and the small endocrine head gland. Its hormones trigger and accelerate molting, and the neurosecretory cells of the eyestalks produce hormones that suppress its activity, that is, preventing the onset of molting. Their content is especially high in the period after molting and between moltings, then the activity of the head gland is activated and preparation for a new molting begins. In addition to those described above, other hormones also take part in the regulation of molting.

Other Life Cycle Features

Some crustaceans, such as daphnia, are characterized by complex life cycles with alternating parthenogenetic and sexual reproduction. In addition, generations of daphnia living at different times of the year experience seasonal changes, expressed in changes in the shape of the head, the length of the rostrum, spines, etc.

Ecology and lifestyle

Spreading

In the seas and oceans, crustaceans are as widespread as insects on land. Crustaceans are diverse in fresh water bodies, and some branchiopods are found in temporary puddles remaining after snow melts. Another branchiopod crustacean - Artemia salina- lives in saline reservoirs in steppes and semi-deserts: in estuaries, salt lakes.

Nutrition

Most planktonic crustaceans feed on bacteria, as well as unicellular organisms and detritus. Bottom-dwelling representatives feed on particles of organic matter, plants or animals. Amphipods eat animal corpses, thereby helping to cleanse water bodies.

A number of studies have been conducted on crab feeding behavior. Portunus pelagicus, in which the animal’s reactions to specific nutrients were studied and also compared with reactions to natural foods (fish, shellfish). As a result, it was found that the reaction of the crustacean to some amino acids and saccharides was the same as to natural food, and the reactions to amino acids and saccharides were very similar. Particularly strong responses were observed to alanine, betan, serine, galactose and glucose. These data may be useful for crab aquaculture.

Shieldfish are characterized by an ancient type of nutrition, which also occurred among trilobites: they feed on pieces of detritus and small bottom animals, which are captured by the chewing processes of all legs and then transmitted along the ventral groove to the mouth.

Practical significance

Crustaceans are an important fishery, including shrimp, crabs, spiny lobsters, langoustines, crayfish, lobsters, and various balanus, including sea duck (or persebes), which is the most expensive of the gourmet crustaceans.

Classification

Currently, more than &&&&&&&&&073000.&&&&&0 73,000 species of crustaceans are known (including more than 5 thousand fossil species), united in 1003 families, more than 9,500 genera (Zhang, 2013), 42 orders and 6 classes:

  • Class Branchiopoda - Branchiopods
    • Subclass Phyllopoda - Leaf-footed
    • Subclass Sarsostraca - Sarsostraca
  • Class Cephalocarida - Cephalocaridae
  • Class Malacostraca - Higher crayfish
    • Subclass Eumalacostraca - Eumalacostraca
    • Subclass Hoplocarida - Hoplocaridae
    • Subclass Phyllocarida - Phyllocaridae
  • Class Maxillopoda - Maxillopoda
    • Subclass Branchiura - Carp lice
    • Subclass Copepoda - Copepods
    • Subclass Mystacocarida - Mystacocaridae
    • Subclass Pentastomida - Fivemouths
    • Subclass Tantulocarida - Tantulocaridae
  • Class Ostracoda - Shells
  • Class Remipedia - Remipedia

According to the latest data, crustaceans also include insects - the class Hexapoda, which are the sister group of branchiopods. If this concept is accepted (the concept of Pancrustacea or Tetraconata, see, for example), the taxonomic position of crustaceans has to be changed (for example, the presence of two pairs of antennas is no longer a common feature for them). Otherwise, crustaceans turn out to be a paraphyletic taxon.

Alternative classification

The classification presented above is not shared by all taxonomists. The site uses another one, which is distinguished primarily by the dissolution of the garbage class of maxillopods and the separation of two superclasses. Classification up to subclasses inclusive:

  • Class Branchiopoda - Branchiopods
    • Subclass Phyllopoda - Leaf-footed
    • Subclass Sarsostraca - Sarsostraca
  • Class Cephalocarida - Cephalocaridae
  • Class Remipedia - Remipedia
  • Superclass Multicrustacea
    • Hexanauplia class
      • Subclass Copepoda - Copepods
      • Subclass Tantulocarida - Tantulocaridae
      • Subclass Thecostraca - Tecostraca
    • Class Malacostraca - Higher crayfish
      • Subclass Eumalacostraca - Eumalacostraca
      • Subclass Hoplocarida - Hoplocaridae
      • Subclass Phyllocarida - Phyllocaridae
  • Superclass Oligostraca
    • Subclass Mystacocarida - Mystacocaridae
    • Class Ichthyostraca
      • Subclass Branchiura - Carp lice
      • Subclass Pentastomida - Fivemouths
    • Class Ostracoda
      • †Subclass Archaeocopa
      • †Subclass Bradoriida
      • † Subclass Metacopa
      • Subclass Myodocopa - Myodocopa
      • Subclass Palaeocopa
      • Subclass Platycopa
      • Subclass Podocopa - Podocopa

see also

  • List of crustaceans listed in the Red Book of Russia

Notes

  1. Shevyakov V. T.// Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
  2. Subtype Crustacea(English) in the World Register of Marine Species. (Accessed May 27, 2017).
  3. Zhang Z.-Q. Phylum Athropoda // Animal Biodiversity: An Outline of Higher-level Classification and Survey of Taxonomic Richness (Addenda 2013) (English) // Zootaxa: monograph; magazine / Zhang, Z.-Q. (Ed.). - Auckland, New Zealand: Magnolia Press, 2013. - Vol. 3703, no. 1 . - P. 17-26. - ISBN 978-1-77557-248-0 (paperback), ISBN 978-1-77557-249-7 (online edition). - ISSN 1175-5326. - DOI:10.11646/zootaxa.3703.1.6. (Retrieved March 7, 2015)
  4. Martin J. W., Davis G. E. An Updated Classification of the Recent Crustacea. - Los Angeles: Natural History Museum of Los Angeles County, 2001. - 132 p. (English) (PDF)
  5. , With. 348.
  6. , With. 293.
  7. , With. 363.
  8. Kornev P. N. The first discovery of representatives of the subclass Tantulocarida in the White Sea // Invertebrate Zoology: journal. - 2004. - T. 1, No. 1. (PDF)
  9. Kornev P. N., Chesunov A. V. Tantulocarids are microscopic inhabitants of the White Sea // Nature: magazine. - 2005. - No. 2. (PDF)
  10. McClain C. R., Boyer A. G. Biodiversity and body size are linked across metazoans (English) // Proceedings of the Royal Society B: Biological Sciences: magazine. - 2009. - Vol. 296, no. 1665. - P. 2209-2215. - DOI:10.1098/rspb.2009.0245. - PMID 19324730. (Retrieved March 2, 2015)
  11. Crustacea - National History Museum
  12. , With. 349.
  13. Crustaceans // Great Soviet encyclopedia: [in 30 volumes] / ch. ed. A. M. Prokhorov. - 3rd ed. - M.: Soviet Encyclopedia, 1969-1978.
  14. Crustaceans- article from the Biological Encyclopedic Dictionary
  15. , With. 295.
  16. , With. 296.

While photographing a snail in an aquarium (photo later), I wondered what the name of the science that studies snails is.

And this is what turned out.

malacology - the science that studies mollusks

A branch of zoology devoted to the study of soft-bodied mollusks (Mollusca). The name comes from the Greek word malakion - mollusk. Scientists who study mollusks are called malacologists. Malacology examines issues of systematics and phylogeny, zoogeography, biology and ecology of mollusks, etc.

One of the sections of malacology is conchology(conchiology) - dedicated to the study of mollusk shells. Conchology - a section of malacology that studies mollusk shells. In a broad sense, it is a scientific, semi-scientific, or amateur study of the shells of soft-bodied animals such as Mollusks.

Hippology- the science of horses, studies anatomy, physiology, reproduction biology, breed formation. Until the 30s. In the 20th century, hippology was taught in cavalry and artillery schools and other special educational institutions. In Russian it will sound like horse breeding, but probably still more in-depth.

I immediately remembered entomology– childhood hobby, studying insects and its subsections arachnology, studying spiders and acarology- a science that studies ticks, and a number of others that study small taxa of arachnids (scorpions, harvestmen, pseudoscorpions, phalanges and others).

Well, since there was such a booze...

Apiology- the science that studies bees (honeybees)

Herpetology- a branch of zoology that studies amphibians and reptiles. Its subsection serpentology- studying snakes. Sometimes the science of amphibians is called batrachology(from Greek - frog).

Carcinology– studies crustaceans. Sections of carcinology also deal with large or practically significant groups. So, copepod studies copepodology, cladoceran - cladocerology, decapod - decapodology

Ketology– studies cetaceans (dolphins, killer whales and naturally whales)

Myrmecology- a subsection of entomology that studies ants.

Nematology(Nematology, nematodology) - a branch of zoology that studies roundworms of the Nematoda type, which is one of the largest in the animal kingdom in terms of the number of species (80,000 species have been described, up to 500,000 are expected)

Oology- a department of zoology devoted to the study of animal eggs, mainly birds. Oology is also sometimes understood as collecting bird eggs.

Ornithology– the term is well known; this science studies birds.

Planktology– it’s pretty clear here – studies plankton

Theriology, also known as mammology, studies mammals; its subsections are ketology and primatology

Chiropterology– studies bats, such as bats.

Ethology– studies animal behavior, closely related to animal psychology.