The structure of crayfish, which is representative of the type of arthropods, is associated with its habitat. This is a typical inhabitant of freshwater bodies, which breathes with the help of gills. This article will be considered crayfish. The structure, pictures, habitat and peculiarities of life are presented below.
Characteristic features of crustaceans
Like all arthropods, the structure of the crayfish (the figure below shows it) is represented by a segmented body and limbs. This is the head, chest and abdomen. Segments of the body are paired limbs, consisting of separate segments. They are able to make quite complex movements. Articular limbs usually attach to the thoracic segments of the body. The external structure of crayfish is fully consistent with the characteristic features of arthropods.
Crayfish can be found in freshwater. Moreover, their presence can be considered an indicator of its environmental safety. After all, these animals prefer reservoirs with pure water and high oxygen content. The structure of crayfish determines their ability to crawl with walking legs or swim. During the day, they are in natural shelters. At night, they crawl out of their holes, from under stones and logs. At this time they are looking for food. In this regard, crayfish are not picky. They are generally omnivorous. Worms, fry, tadpoles, clams, algae - all of them will like crayfish. They do not disdain and dead organic matter. If you decide to have this animal in your home aquarium, not only special food will be suitable for eating, but also meat, vegetables and bread. True, while maintaining clean water will be quite difficult.
External structure of crayfish
The body of crayfish consists of two parts. This is the head and abdomen. The front part is covered with so-called shell. And the abdomen consists of individual segments, on top of which are small shields. The head of the head also contains two pairs of antennae, an oral apparatus, and five pairs of walking legs. Each of them performs certain functions. For example, the first pair ends with powerful claws that serve to grab food, tear it into pieces and protect it from enemies.
Six pairs of limbs are attached to the abdomen. The last pair of legs is dilated and forms the caudal fin together with the anal plate. In appearance, it resembles a fan. With the help of the anal fin, river crayfish rather quickly float posteriorly forward. Together, they have 19 limbs.
The structural features of a crayfish are primarily determined by its cover. Like all arthropods, it is represented by the cuticle, which forms a powerful outer skeleton. Calcium carbonate gives it additional hardness.
Since the cuticle is not capable of stretching, the growth of crayfish is accompanied by periodic molts. This period is critical in the life of these aquatic inhabitants. A few days before the crabs become restless, stop eating, and all the time they spend in search of shelter. With the help of intensive movements of the body and limbs, they get rid of the old cover, from which they crawl out through a gap at the border of the cephalothorax and abdomen. In their secure shelter, crayfish remain for up to ten days, until a new cuticle hardens.
Internal structure of crayfish
During embryonic development in all arthropods, a secondary body cavity is laid. But it does not persist throughout the life of the animal. In the process of individual development, this structure is destroyed, merging with the remnants of the primary and forming a mixed cavity. The gaps between the organs are filled with crustaceans in the fatty body. This is a kind of loose connective tissue that performs important functions: storing nutrients, forming blood cells, protecting against mechanical damage.
Major organ systems
The internal structure of crayfish is represented by rather complex organ systems. Digestive - end-to-end, with the presence of the liver and salivary glands, which secrete enzymes that break down nutrients. The end products of metabolism are removed from the body with the help of the excretory system represented by malpighian vessels.
The respiratory organs of crayfish are caused by the aquatic environment of its habitat, these are the gills. The circulatory system is closely connected with them. She is unlocked. The blood vessels open into the body cavity, mix with its fluid, forming a hemolymph. It transports oxygen, carbon dioxide, nutrients, metabolic products.
The most important function of hemolymph is protective. It contains specialized cells, which carry out amoeboid movements, seize pathogens and digest them with common pseudopods. Movement of the hemolymph in the body provides a pulsating thickened vessel - the heart. Since blood is mixed with cavity fluid and is not divided into arterial and venous, crayfish is cold-blooded animals. This means that the temperature of his body decreases with a cooling in the environment.
In late autumn, crayfish begin to multiply. These are dioecious animals with direct development and external fertilization. The male has a testis and two seed lines, the female has an ovary and paired oviducts. After fertilization, the eggs are on the female's abdomen. So she shows maternal instinct, caring for future offspring. In late spring or early summer, young crustaceans emerge from them, which are an exact copy of adult individuals.
The nervous system is also rather complicated. It consists of differentiated departments: front, middle and rear. The first regulates the work of the eyes, provides complex behavioral reactions of these animals, the rest innervate the antennae. The brain is anatomically connected to the ventral nerve chain, from which individual nerve fibers extend along the body.
Value in nature and human life
Juveniles of crayfish form plankton of freshwater bodies - an important link in the food chain. Using the dead animals for food, they clean the habitat. Recently, due to the negative influence of humans, the number of river cancer populations has sharply decreased. In dirty water, the offspring of crayfish inevitably awaits death. This is also due to the important commercial significance of this representative of arthropods. After all, crayfish meat is a valuable food product, and in some regions even a delicacy. It is rich in proteins, vitamins and microelements. Crayfish is the largest representative of the class that lives in freshwater. To preserve this species in nature, their fishing is officially prohibited until mid-summer.
The structure of crayfish is largely due to its habitat and determines its importance in nature and human life.
Biology: the structure of crayfish
Let's start with the basics of classification. This animal is representative of the type Arthropods. They are characterized by the presence of a segmented body and limbs, an external skeleton and a mixed body cavity.
The animal that we study belongs to the class of crustaceans. His closest "relatives" are Daphnia, Shchitni, Cyclops, Carpedoids and Crabs. Two other classes of arthropods are Spider-like and Insect.
Crayfish is quite an ancient representative of the animal world. This species appeared already in the Jurassic period 130 million years ago. Its fossil forms indicate minor evolutionary changes.
The internal structure of crayfish is determined by the embryonic development. During this period, the animals laid the secondary body cavity. But as it develops, it collapses, mixing with the remnants of the primary. Thus, a mixed body cavity, characteristic of all crustaceans, is formed. Its characteristic feature is the presence of a fatty body. It is a loose connective tissue that fills the gaps between the organs.
An interesting fact is that female crayfish are much more voracious than males. This is especially pronounced during the mating period. And what do these species feed on? They are almost omnivorous. But the food they find by smell, so it must always have a "flavor". Their plant ration is represented by algae, foliage of coastal trees, sedge, elodea, water buckwheat, horsetail, water lilies. In winter, food is dry foliage.
Animal food also differs a considerable variety. These are insect larvae, clams, tadpoles and frogs, small or sick fish, young crayfish. These animals are especially not indifferent to carrion. But it should not be completely decomposed.
To hunt the crabs go at night, and in the daytime they hide in shelters. They can be burrows, tree roots, stones. The composition of food depends on the stage of the life cycle of the crustaceans. Thus, in the period of mating and molting, they need a more high-calorie food of animal origin.
Digestion and Excretion
The digestive system of the crayfish is represented by the mouth, pharynx, esophagus, stomach, intestines, ending with the anus. It has its own characteristics. So, the stomach consists of two sections. In a larger one, food is ground with the help of chitinous teeth, while in the second it is filtered through a filtering device. Another feature is that the final process of splitting and absorption of substances occurs in the digestive gland. Food comes to this organ from the intestines.
Green glands are organs of excretion. They are paired. From them depart excretory tubules, which open in the area of the base of the antennae. The products of their excretion are toxins dissolved in the blood.
Circulatory and respiratory system
The structure of crayfish has a number of progressive features. For the circulatory system is the appearance of the heart. She is unlocked. This means that the blood from the vessels enters the body cavity, washing all the organ systems. At the same time oxygen is supplied to the cells. At the same time they get rid of carbon dioxide. It enters the respiratory system - gills, and enters the water. From here, crustaceans get oxygen.
Components of this system are the pharyngeal ring, abdominal chain, supra- and subpharyngeal nodes. From them to the organs and limbs depart nerve fibers. Cancer has sensory systems of vision, hearing, touch, smell, balance. Eyes have a particularly complex structure. They are on special stalks. Each of them consists of numerous simple ocelli, which perceives only part of the image. And in the aggregate, the correct "picture" is being formed. Such a vision is called mosaic.
The structure of crayfish is closely interrelated with seasonal phenomena and cancer lifestyle. With a decrease in daylight, their activity begins to decrease. The process of reproduction begins in the fall. These are animals with an external type of fertilization, therefore the eggs attach to the abdominal legs of the female. This is how crayfish take care of their offspring, in which they spend the whole autumn and winter. At one time, the female allocates up to 600 eggs, which bears half a year.
With the onset of cold weather crayfish descend deeper and lead a sedentary lifestyle. Caviar larvae appear only in summer. Outwardly, they are an exact copy of adults. This type of development is called direct. During this period, crayfish are collected at coastal sites. This is because the final stage of development of fertilized eggs requires special conditions. These include higher temperature and oxygen levels.
So, in our article we looked at the structure of crayfish and the peculiarities of its vital activity. Its main features include:
- aquatic habitat,
- body of cephalothorax and abdomen,
- 19 pairs of limbs that allow crayfish to walk on the bottom, swim, hunt, keep food, defend themselves from enemies,
- mixed body cavity,
- removal of metabolic products through green glands,
- the presence of the heart, an open circulatory system,
- the nervous system of the node type,
- isolation, external fertilization, direct development.
River crayfish lives in various freshwater reservoirs with clear water: river creeks, lakes, large ponds. During the day, crayfish hide under stones, snags, and roots of coastal trees, in their burrows, dug by themselves in the soft bottom. In search of food, they leave their shelters mostly at night. It feeds mainly on plant food, as well as dead and live animals.
The 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 filtering. On the dorsal and lateral walls of the chewing section there are three powerful lime-infused chitinous chewing plates with jagged free edges. In the filtering department, two plates with hairs act like a filter through which only strongly powdered food passes. Large pieces of food linger and return to the first section, while small ones enter the intestine.
Then the food enters the midgut, where the ducts of the large digestive gland open.
Under the action of secreted enzymes, food is digested and absorbed through the walls of the midgut and the glands (it is called the liver, but its secret breaks down not only fats, but also proteins and carbohydrates). Undigested remnants enter the posterior intestine and are expelled through the anus on the caudal blade.
In cancer, the body cavity is mixed, it is not blood that circulates in the vessels and intercellular cavities, but a colorless or greenish liquid - hemolymph. It performs the same functions as blood in animals with a closed circulatory system.
On the dorsal side of the cephalothorax under the scute is a pentagonal heart, from which blood vessels depart. The vessels open into the body cavity, the blood gives up oxygen and nutrients there to the tissues and organs, and collects waste products and carbon dioxide. Then the hemolymph enters the gills through the vessels, and from there into the heart.
The respiratory organs of cancer are the gills. They contain blood capillaries and gas exchange. The gills have the appearance of thin feathery outgrowths and are located on the processes of the maxillary and walking legs. In the cephalothorax the gills lie in a special cavity.
The movement of water in this cavity is due to the rapid oscillations of special processes of the second pair of lower jaws), and up to 200 flapping movements are performed in 1 minute.) Gas exchange occurs through the thin shell of the gills. Oxygen-enriched blood through the gill-heart valves is sent to the pericardial bag, from there through special holes into the heart cavity.
On both pairs of antennae there are receptors: tactile, chemical feelings, balance. Each eye contains more than 3,000 eyes, or facets, separated from each other by thin layers of pigment. The light-sensitive 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, so they say that arthropods have mosaic vision).
The organs of equilibrium represent a depression 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.
The organs of excretion are represented by a pair of green glands located in the anterior part of the cephalothorax (at the base of the long antennae and open outwards). Each gland consists of two parts - the gland itself and the bladder.
In the bladder accumulate harmful waste products formed in the process of metabolism, is displayed outside the excretory channel through the excretory pore. The excretory gland in its origin is nothing else but a modified metanephridium. It begins with a small coelomic sac (in general, harmful metabolic products come from all organs of the body), from which a tortuous tube departs - the glandular canal.
In crayfish developed sexual dimorphism. Fertilization is internal. In males, the first and second pair of abdominal legs are modified into a copulatory organ. In the female, the first pair of abdominal legs is rudimentary; on the other four pairs of abdominal legs, it bears eggs and young crustaceans.
Fertilized eggs laid by the female (60-200 pieces) are attached to her abdominal legs. Egg laying occurs in winter, and young crustaceans (similar to adults) appear in spring. After hatching from eggs, they continue to hold on to the mother's abdominal legs, and then leave her and begin an independent life. Young crustaceans eat only plant food.
Adult crayfish molt once a year. Сбросив старый покров, они 8-12 дней не покидают укрытий и дожидаются, пока затвердеет новый. В этот период тело животного быстро увеличивается.
В основном, ведут водный образ жизни, но есть также амфибиотические и сухопутные формы из числа равноногих ракообразных, десятиногих и амфипод. Among crustaceans, there are both free-living and parasitic forms.
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Nutrition and Digestion
Cancer feeds on a variety of foods. He likes the rotting corpses of various animals and feels them at a great distance. He willingly attacks various living, mostly sedentary animals: mollusks (shells of small ones he breaks with his claws), insect larvae. It eats cancer and plants, especially chararium-rich algae rich in calcium, and young crustaceans feed only on plants.
The mouth of the cancer is surrounded by transformed legs (Fig. 69A): one pair turns into the upper jaws, two pairs - into the lower jaws, three pairs - into the maxilla. They all serve to hold, grope and grind food.
Extraction crayfish claws enough, if it is large, tears pieces from it. These pieces move to the mouth with the jaws, then the jaws tear it into even smaller pieces and send it into the mouth. In the stomach, food is still crushed and, finally, enters the intestine, where it is digested and absorbed. The anus of the cancer is located on the tail segment of the abdomen.
Breathing and respiratory system
The respiratory organ of the cancer is the gills (Fig. 69B), which in the form of thin feathery outgrowths are placed in a special chamber under the cephalothorax.
Water enters them through the small holes at the base of the chest legs and out through the hole near the mouth. The water flow is due to continuous, very fast (100-200 times per minute) oscillations of the second pair of jaws. The gills are shrouded in a network of blood capillaries.
Gas exchange is carried out in the gills.
Reproduction and development
Reproduction in cancer is sexual. River crayfish dioecious, internal fertilization. Material from the site http://doklad-referat.ru
Egg laying occurs in winter. Eggs, in the amount of 60-200 pieces are glued to the abdominal legs of the female. Their development lasts several months, young crustaceans appear in spring. At first, they continue to hold on to the female's abdominal legs, then proceed to independent living. For crayfish, direct development is characteristic when a microscopic, almost formed animal resembling an adult appears from the egg. Molting occurs in young crustaceans several times a year, and since the third year of life in males twice, in females once a year. During the molting, when the old chitinous cover is discarded, the outer covers are soft and the cancer is not only defenseless, but it can neither catch nor chew the prey. Therefore, until a new chitinous shell is cured, and this takes 8–10 days, the cancer is still sitting in its shelter. Crayfish live up to 20 years.