Representatives of crustaceans are examples. Interesting facts about crustaceans

Crustaceans are aquatic arthropods that breathe with gills. The body is divided into segments and consists of several sections: from the head, chest and abdomen or from the cephalothorax and abdomen. There are two pairs of antennae. The integuments of the body contain a special solid substance - chitin, and in some, they are also reinforced (impregnated) with calcium carbonate.

About 40 thousand species of crustaceans are known (Fig. 85). Their sizes are varied - from fractions of a millimeter to 80 cm. Crustaceans are widespread in the seas and fresh water, a few, such as woodlice, palm thief, switched to a terrestrial way of life.

Rice. 85. Various crustaceans: 1 - crab; 2 - hermit crab; 3 - shrimp; 4 - wood lice; 5 - amphipod; 6 - sea duck; 7 - shield

Features of the structure and vital activity of crustaceans can be considered on the example of crayfish.

Lifestyle and external structure. Crayfish lives in various fresh water bodies with clean water: river backwaters, lakes, large ponds. During the day, crayfish hide under stones, snags, roots of coastal trees, in minks dug by themselves in the soft bottom. In search of food, they leave their shelters mainly at night.

Crayfish - pretty major representative arthropods, sometimes there are specimens over 15 cm long. The color of crayfish is greenish-black. The whole body is covered with a strong and dense chitinous shell, impregnated with calcium carbonate.

covers crayfish serve as an external skeleton. Bundles of striated muscles are attached to it from the inside. The hard shell of cancer prevents the animal from growing. Therefore, cancer periodically (2-3 times a year) sheds - sheds old integuments and acquires new ones. During molting, until the new shell gets stronger (it takes about a week and a half), the crayfish is defenseless and cannot eat. At this time, he hides in shelters. The body of crayfish consists of two sections - the cephalothorax and abdomen (Fig. 86). At the front end of the cephalothorax there is a pair of long and a pair of short antennae - these are the organs of touch and smell. Globular eyes sit on long stalks. Therefore, cancer can simultaneously look in different directions. In case of danger, he hides his eyes in the recesses of the shell.

Rice. 86. External structure of crayfish: 1 - long antennae; 2 - short antennae; 3 - claw; 4 - walking legs; 5 - eye; 6" - cephalothorax; 7 - abdomen; 8 - caudal fin

Cancer eyes are complex. Each eye consists of many very small eyes, facets, directed in different directions (Fig. 87, B). The image of an object in a complex (faceted) eye is made up of its individual parts, resembling mosaic pictures.

Rice. 87. Internal structure of crayfish (female): A - general plan of body structure: 1 - stomach; 2 - liver; 3 - heart; 4 - blood vessels; 5 - ovary; 6 - gut; B - diagram of the structure of the compound eye

Limbs are located on the cephalothorax of crayfish. If it is turned over on its back, then at the front end of the body one can find three pairs of jaws: a pair upper jaws and two couples lower jaws. With them, cancer breaks prey into small pieces. The jaws are followed by three pairs of short mandibles. They serve to bring food to the mouth. Both jaws and mandibles are modified legs. Behind the mandibles are five pairs of walking legs. With the help of four pairs of these legs, the crayfish moves along the bottom of the reservoirs. And the first pair of walking legs in cancer is turned into large claws. With them, cancer seizes prey, tears off large parts from it. With the same claws he defends himself.

And on the abdomen, the cancer has short limbs (legs), the female has four of them, the male has five pairs. At the very end of the abdomen there is a flat segment, on the sides of which modified, strongly flattened legs are developed. Together they form the tail fin. Sharply bending the abdomen, the crayfish is repelled from the water by its caudal fin, like an oar, and in case of danger it can quickly swim backwards.

Digestive system (Fig. 87, A) begins with the mouth opening. From the mouth, food enters the stomach, which consists of two sections. In the first section there are chitinous formations impregnated with calcium carbonate - millstones, with the help of which food is crushed. Then it ends up in the second section of the stomach, where it is filtered. Large food particles are retained and returned to the first section, while small ones enter the intestine. The ducts of the liver flow into the middle intestine. Digestion of food and absorption of nutrients occur in the intestines and liver. The digestive system ends with an anus located on the caudal segment of the abdomen. Crayfish feed on mollusks, insect larvae living in water, decaying animal corpses, and plants.

Respiratory organs crayfish have gills. They contain blood capillaries and gas exchange takes place. The gills look like thin feathery outgrowths and are located on the processes of the mandibles and walking legs. In the cephalothorax, the gills lie in a special cavity. The movement of water in this cavity is carried out due to very rapid vibrations of special processes of the second pair of jaws.

Circulatory system open.

In crustaceans, the body cavity is mixed; in the vessels and intercellular cavities of crustaceans (as in other arthropods), it is not blood that circulates, but a colorless or greenish liquid - hemolymph. It performs the same functions as blood and lymph in animals with a closed circulatory system.

The heart is located on the dorsal side of the cephalothorax. Hemolymph flows through the vessels, and then enters the cavities located in various organs. Here the hemolymph gives nutrients and oxygen, but takes in waste products and carbon dioxide. Then the hemolymph enters the gills through the vessels, and from there to the heart.

excretory system represented by a pair of green glands located in front of the cephalothorax. They open outward at the base of the long antennae. Through these holes are removed harmful products that are formed in the course of life.

Nervous system. Cancer has a central nervous system - a peripharyngeal nerve ring and an abdominal nerve chain and a peripheral nervous system - nerves extending from the central nervous system.

Sense organs. In addition to the organs of touch, smell and vision, crayfish also have organs of balance. They represent a recess in the main segment of the short antennae, where a grain of sand is placed. The grain of sand presses on the thin, sensitive hairs surrounding it, which helps the cancer to assess the position of its body in space.

Reproduction. River cancer is characteristic sexual reproduction. Fertilization is internal. Fertilized eggs laid by the female (from 60 to 200 pieces) are attached to her ventral legs. Egg laying occurs in winter, and young crustaceans appear in spring. Having hatched from the eggs, they continue to hold on to the mother's abdominal legs (Fig. 88), and then leave her and begin an independent life. Young crustaceans eat only plant foods.

Rice. 88. Young crustaceans on the ventral legs of a female

Decapods include crayfish, large sea crayfish - lobsters (up to 60 cm long and weighing up to 15 kg) and lobsters (they do not have claws), small crustaceans - shrimp. Some of them move along the bottom, others actively swim in the water column with the help of abdominal legs. Hermit crabs belong to this group. They have a soft, unsegmented abdomen. Hermit crabs hide from enemies in the empty shells of sea snails, all the time carrying the shell with them, and in case of danger, completely hiding in it, covering the entrance with a highly developed claw. Crabs are decapods. They have a wide but short cephalothorax, very short antennae, and a short abdomen tucked under the cephalothorax. Crabs usually move sideways.

Small crustaceans, well-known to aquarists, belong to the Leaf-legged - daphnia 3-5 mm long (Fig. 89, 1). They live in small fresh water bodies. The entire body (with the exception of the head) of Daphnia is enclosed in a transparent chitinous shell-shell. Through the chitinous covers, a large complex eye and constantly working pectoral legs are visible, which ensure the flow of water under the shell. Daphnia has large, branched antennae. By waving them, she jumps in the water, which is why daphnia is sometimes called "water fleas." Daphnia feed on protozoa, bacteria, unicellular algae located in the water column.

Rice. 89. Crustaceans: 1 - daphnia: 2 - cyclops

A small crustacean, vaguely resembling a wood lice, lives in fresh water bodies - a water donkey. Amphipods are small (up to several centimeters) crustaceans swimming on their side, for which they are called amphipods. Using different legs, crustaceans can swim, walk along the bottom of reservoirs, along the wet soil of the banks, and also jump. Barnacles are small crustaceans that lead an attached lifestyle as adults, such as sea acorns. They live in the sea. Their whole body is covered with a calcareous shell-house. Most often, the shell is attached to stones, crab shells, the bottoms of ships, and whale skin. Barnacles catch their prey (planktonic organisms) with the help of long movable pectoral legs.

Crustaceans are primary aquatic arthropods with a hard and durable chitinous shell impregnated with calcium carbonate, articulated limbs located on the thoracic and abdominal regions. Crustaceans breathe with gills.

Lesson learned exercises

1. Find out, using figure 86, what features in external structure have arthropods. Name the features of their similarity with annelids.
2. What is the difference internal structure crustaceans from representatives of other classes of arthropods? Explain with the example of crayfish.
3. What are the features of the structure of the sense organs in crayfish?
4. Use several examples and drawings to show the diversity of the class. Describe the habitats of crustaceans.
5. What is the role of crustaceans in nature?

Combining more than 30 thousand species. In addition to this group of animals, arthropods include insects and arachnids. According to the classification, the class is divided into 20 orders: leaf-footed (daphnia), decapods (crabs, crayfish, lobsters), isopods (woodlice), copepods (cyclops), etc.

According to some scientists, in the course of evolution, crustaceans evolved from trilobites, according to others - from annelids. Fossil remains of crustaceans have been found in strata of the Cambrian period.

In the building are marked characteristics. The sizes of these organisms vary from fractions of millimeters (tantulokaridy) to 70-80 cm in giant crustaceans (King crab, Tasmanian crab). The body consists of three large sections: the head, chest and abdomen, conventionally divided into segments. Numerous limbs are located on the chest and abdomen of crustaceans. The chest in higher crustaceans consists of eight segments, in other representatives of the class from different quantity segments. In some crustaceans, several anterior thoracic segments are firmly connected to the head, the limbs on them are transformed into mandibles, and the remaining thoracic limbs are designed for movement (often gills are attached to them). In the vast majority of higher crustaceans, the abdomen is represented by six segments with limbs on each. The rest of the segments have a different number of segments, sometimes legs are absent on them. The limbs of animals of this group are biramous. The leg consists of the main part of two or three segments and two segmented branches.

From adverse external influences, the body of crustaceans is protected by a chitinous shell, which delays the continuous growth of animals. In the process of growth, like other arthropods, they undergo molting. The composition of the shell of large decapods of higher crustaceans, in addition to chitin, includes calcium carbonate, due to which the shell becomes much stronger than that of other members of the class.

Food enters from the mouth opening into the chewing stomach and then into the intestines. The ducts of the digestive gland, the “liver,” open into the midgut.

The circulatory system is not closed. The heart in the pericardial sac is located on the dorsal side of the body. The respiratory organs of these animals are the gills, which are fused with the limbs or are located on the sides of the chest and abdomen. In some species, breathing is carried out through the entire surface of the body. The excretory organs are coelomoducts, or antennal glands, the ducts of which open at the base of the antennae.

Most crayfish are dioecious, only barnacles are hermaphrodites, fertilization is external. The eggs hatch into larvae that swim in the water column. With each subsequent molt, the organs of the larva grow, and it becomes more and more like an adult. Some crustaceans are characterized by direct development, when a small, formed crustacean emerges from the egg.

PLAN

1. general characteristics arthropods.

2. Features of the external and internal structure of crustaceans

3. The main representatives of crustaceans

4. General characteristics of arachnids.

5. The main representatives of arachnids.

LITERATURE:

1. V.I. Blinnikov Zoology with the basics of ecology M, Enlightenment 1990

2. I.Kh. Sharova Zoology of invertebrates M, Vlados, 2002.

3. A.A.Yakhontov Zoology for teachers M Enlightenment 1982

4. Animal life 1-3 volumes

general characteristics

The individual classes that make up the type of arthropods can be easily distinguished by their characteristic outward signs, and in particular by the number of limbs.

If an arthropod has two pairs of antennae on its head and many legs, and if at the same time it lives in water or in damp places, then we have a representative class of crustaceans.

If there are no antennae on the head, and four pairs of walking legs, then such an animal belongs to class of arachnids(this includes spiders, scorpions, ticks).

Representatives centipede class body is long and a large number monotonous segments; they have one pair of antennae, and the number of walking legs is at least 15 pairs.

Finally, for class of insects characteristic is the presence of one pair of antennae and three pairs of legs; in addition, the vast majority of adult insects also have wings.

This is the most prosperous group of animals on Earth, which is characterized by high species diversity and high numbers. Currently, more than 1 million 500 thousand species of arthropods are known, which is several times greater than the number of species of all other types of animals.

Arthropod population extremely high . So:

1. Three-layer protostomes multicellular animals

2. The body is segmented. Segmentation is heteronomous. segments of different parts of the body have an unequal structure. Segments are grouped into body parts: head, thorax, abdomen.

3. In the process of evolution, arthropods developed limbs. Their structure (two-branched type) and location (segmental in the lower ones) prove their connection with the parapodia of the annulus. The limbs consist of segments and are movably connected to the body. The functions of the limbs are diverse - they serve as organs of movement in different environments, sense organs, oral apparatus, organs of defense and attack.

4. The body is covered with a chitinized cuticle - a hard outer cover that is formed by the epithelium underlying it. The cuticle consists of a waxy, waterproof outer layer (epicuticle), a hard middle layer (exocuticle), and a flexible inner layer (endocuticle). It serves to protect against drying and mechanical damage.

5. The lumen of the coelom unites with the primary body cavity to form the so-called mixocoel. Remains of the coelom are preserved only around the nephridia and in the gonads.

6. The muscles are divided into separate muscle bundles and are represented by striated tissue.

7. Digestive system - from three sections: anterior, middle and posterior. In the anterior section, due to the chitinous lining, a grinding apparatus is formed. In crustaceans and arachnids, paired outgrowths appear in the midgut - the rudiments of the digestive glands (liver)

8. The circulatory system is open. For the first time in the process of evolution, the heart appears in the form of a muscular sac located on the dorsal side and having paired openings equipped with valves.

9. Respiratory organs are diverse: in water - gills, in terrestrial leaf-shaped lungs or trachea.

10. The nervous system consists of the brain and the ventral nerve chain. The concentration of nerve elements is characteristic, which leads to the release of the brain

11. The excretory system is represented by complicated metanephridia, homologous to metanephridia of the annulus or malpighian vessels. Most arthropods are dioecious. They develop with both complete and incomplete metamorphosis.

Biological significance: arthropods in natural ecosystems is large and multifaceted.

· As constant and numerous components of aquatic and terrestrial ecosystems, they play an essential role in the biological cycle and bioenergetic processes in nature.

· Many aquatic arthropods are important as biofilters in water purification from organic pollution.

· In the soil, the role of arthropods in the processes of soil formation is great.

· Among arthropods, there are many objects of fishing and industrial breeding.

class of crustaceans

The class of crustaceans, which includes crayfish, contains about 25,000 certain types living in the seas and oceans and in freshwater basins. Characteristic features crustaceans, is Firstly , the presence of two pairs of antennae on the head, Secondly , gill breathing, and their gills are either modified limbs or special outgrowths on the limbs.

Crustaceans develop from eggs, and in most crustaceans, females do not lay their eggs somewhere on the side, but carry them on their bodies until the larvae hatch. In some species, like our crayfish, larvae emerge from the testicles, already generally similar to the adult form, but in most other crustaceans, the larvae emerge from the egg at an earlier stage of development in the form of the so-called nauplius. Such larvae have a very short and rounded body with one unpaired eye on the head and only three pairs of limbs with which they swim in the water.

Crayfish

Crayfish in the European part of the USSR belong to two closely related species. West, in the rivers of the basin Baltic Sea, there is a broad-toed, or noble, crayfish with a wider body and massive claws, and narrow-clawed crayfish with more elongated claws has spread widely in the east. With a general similarity in lifestyle, narrow-clawed cancer is more mobile and more prolific; therefore, penetrating (through channels) to the west, it displaces the noble crayfish there (a pronounced example of interspecific struggle).)

The main representatives of crustaceans

Order Crayfish(daphnia) - inhabit ponds and lakes - food for fry of many fish

Order Copepods(cyclops) seas - food marine fish and whales., an intermediate host of tapeworms.

Squad isopods(water donkey, common wood lice, cellar wood lice) - participate in the circulation of org. substances

Squad Decapods(long-tailed - lobsters, lobsters, shrimps, broad-toed and narrow-toed crayfish, soft-tailed crayfish - hermit crab, short-tailed crayfish - real crabs, giant Japanese crab (Zm), stone crab, palm thief.

Similar information.

Which includes the following most famous animals: crabs, lobsters, shrimp, krill, crayfish, wood lice and barnacles. To date, about 70,000 species have been discovered. Crustaceans have evolved in the sea to this day, they are the only subtype of arthropods for which water environment is the main one. There are several terrestrial crustacean species (eg land crabs, land hermit crabs and wood lice) as well as several parasitic groups (eg whale lice and fish lice). Most crustaceans are mobile, but some groups, such as barnacles, are sedentary.

Description

The body of crustaceans is divided into the following sections: head, thoracic and abdominal. In some species, the head and thorax are fused together (cephalothorax). Crustaceans have an external skeleton (exoskeleton). The cuticle (outer layer) is often reinforced with calcium carbonate, which provides additional structural support (especially true for large species).

Many species of crustaceans have five pairs of appendages on the head (these include: two pairs of antennae (antennae), a pair of lower jaws (maxillas) and a pair of upper jaws (mandibles, or mandibles)). The compound eyes are located at the end of the stalks. Rib cage contains several pairs of pereiopods (walking legs), and a segmented belly pleopods (ventral legs). The posterior end of the crustacean body is called the telson. Large species of crustaceans breathe with gills. Small species for gas exchange using the surface of the body.

reproduction

Most species of crustaceans are heterosexual and reproduce sexually, although some groups, such as barnacles, remipedians, and cephalocarids, are hermaphrodites. The crustacean life cycle begins with a fertilized egg, which is either released directly into the water or attached to the genitals or legs of the female. After hatching from an egg, crustaceans go through several stages of development before turning into an adult.

food chain

Crustaceans occupy a key place in the sea and are one of the most common animals on Earth. They feed on organisms such as phytoplankton, in turn, crustaceans become food for larger animals such as fish, and some crustaceans such as crabs, lobsters and shrimp are a very popular food for humans.

Dimensions

Crustaceans come in a wide variety of sizes from microscopic aquatic fleas and crustaceans to the giant Japanese spider crab, which reaches a mass of about 20 kg and has legs 3-4 m long.

Nutrition

In the process of evolution, crustaceans have acquired a wide range of feeding habits. Some species are filter feeders, extracting plankton from the water. Other species, especially large ones, are active predators that grab and tear their prey with powerful appendages. There are also scavengers, especially among small species that feed on the decaying remains of other organisms.

First crustaceans

Crustaceans are well represented in the fossil record. The first representatives of crustaceans belong to the Cambrian period and are represented by fossils mined in the Burges Shale Shale Formation, located in Canada.

Classification

Crustaceans include the following 6 classes:

• Gillnopods (Branchiopoda);
• Cephalocarids (Cephalocarida);
• higher crayfish (Malacostraca);
• Maxillopods (Maxillopoda);
• Shellfish (Ostracoda);
• crested (remipedia).

The body of representatives of the class Crustacea is covered with a hard shell and consists of a cephalothorax and abdomen. Unlike other arthropods, crustaceans have 2 pairs of antennae on their heads - long (organs of touch) and short (organs of smell).

Crayfish breathe with gills located on the sides of the body, under the shell of the cephalothorax.

Eyes

Cancer eyes are complex. They are made up of many facets, up to 3 thousand. Due to the weak mobility of the cephalothorax, the eyes of crayfish are located on stalks, which it can turn in different directions. In case of danger, he hides them in the recesses of the shell.

limbs

Three pairs of modified limbs form a mouth, 3 more pairs form the jaws. Cancer has 5 pairs of ho-dil legs, among which the first one with highly developed claws stands out externally.

Life cycle

The largest group of crustaceans decapods crayfish. It includes all known species: crayfish, crabs, lobsters, shrimps, lobsters. They are especially diverse in the shallow waters of tropical seas. There are freshwater species, for example crayfish, and ground- robber crab, alluring crab, hermit crab.

Barnacles- the only group of sessile forms among crustaceans. They are found only in the seas. Barnacles secrete a secret to build a complex calcareous shell, inside which they live. Examples of free-living barnacles are sea ​​ducks And sea ​​acorns.

The simplest structure is leaf-footed. These include mainly freshwater species, For example daphnia(water fleas). material from the site

Numerous species of crustaceans make up the bulk of zooplankton - communities of small animals that inhabit the water column and are passively carried by the current. These crustaceans are the main food for fish and aquatic mammals.

Like all animals, crayfish play the role of consumers. They feed mainly on worms, insect larvae. Crustaceans that feed on dead organisms are actively involved in the processes of self-purification of reservoirs.