Crustacean chordates. Crustaceans - description, characteristics, nutrition, reproduction and classification. Daphnia, or water fleas
Crustaceans- These are aquatic arthropods or inhabitants of wet places. Their body sizes range from a few millimeters to 1 m. They are distributed everywhere; lead a free or attached lifestyle. The class has about 20 thousand species. Only crustaceans are characterized by the presence of two pairs of antennae, two-branched limbs and gill breathing. The class Crustaceans includes 5 subclasses. Conventionally, all representatives are divided into lower (daphnia, cyclops) and higher crayfish (lobster, lobster, shrimp, river crayfish).
Representative of higher cancers - crayfish. It lives in fresh water bodies with running water, leads night look life and is a predator.
Crayfish. External and internal structure:
1 - Antennae, 2 - Claw, 3 - Walking legs, 4 - Caudal fin, 5 - Abdomen, 6 - Cephalothorax, 7 - Cephalic ganglion, 8 - Digestive tube, 9 - Green gland, 10 - Gills, 11 - Heart, 12 — Sex gland
The body of the cancer is covered with a dense chitinous shell. The fused segments of the head and chest form the cephalothorax. Its front part is elongated and ends with a sharp spike. In front of the spine there are two pairs of antennae, and on the sides on movable stalks there are two compound (compounded) eyes. Each eye contains up to 3 thousand small ocelli. Modified limbs (6 pairs) form oral apparatus: the first pair - the upper jaws, the second and third - mandibles, the next three pairs are the maxillaries. The thoracic region bears 5 pairs of jointed limbs. The first pair is the organ of attack and defense. It ends in powerful claws. The remaining 4 pairs are walking limbs. The limbs of the segmented abdomen are used in females to bear eggs and young. The abdomen ends with a caudal fin. When a crayfish swims, it scoops up water with it and moves with its tail end forward. Bundles of striated muscles are attached to the internal projections of the chitinous cover.
Cancer feeds on both living organisms and decaying animal and plant debris. The crushed food passes through the mouth into the pharynx and esophagus, then into the stomach, which has two sections. The chitinous teeth of the chewing section grind food; in the filter stomach it is filtered and enters the midgut. The ducts of the large digestive gland, which performs the functions of the liver and pancreas, also open here. Under the influence of its secretion, food gruel is digested. Nutrients are absorbed, and undigested residues are thrown out through the hindgut and anus.
The excretory organs of cancer are a pair of green glands (modified metanephridia) that open at the base of the long antennae. Respiratory organs are gills located on the sides of the cephalothorax. They are penetrated by blood vessels in which gas exchange occurs - blood gives off carbon dioxide and is saturated with oxygen. Circulatory system open It consists of a pentagonal heart located on the dorsal side and the vessels extending from it. Blood pigment contains copper, so it of blue color. The nervous system of crayfish resembles nervous system annelids. It consists of the suprapharyngeal and subpharyngeal ganglia, united in a peripharyngeal ring, and the abdominal nerve cord. The organs of vision, touch and smell (on the antennae), and balance (at the base of the short antennae) are well developed. Cancers are dioecious. Reproduction is sexual, development is direct. Eggs are laid in winter, and small crayfish hatch from eggs in early summer. Cancer expresses concern for offspring.
The meaning of crustaceans. Crustaceans serve as food for aquatic animals and as food for humans (lobsters, crabs, shrimp, crayfish). They clear water bodies of carrion. Certain representatives of crustaceans cause fish diseases by settling on their skin or gills; some are intermediate hosts of tapeworms and roundworms.
Class Crustaceans (Crustacea)
The Crustacea class includes a wide variety of arthropods. This includes, often not similar friend animals like crabs and woodlice, both in appearance and in their way of life, crayfish and shrimps, hermit crabs and carp lice, lobsters and water fleas... And since adult crustaceans are very diverse in shape, then give them brief description, clearly distinguishing them from other groups of animals is almost impossible. Therefore, evolutionary (genetic) family ties between different representatives of the class are established only by the characteristics of their larval development. And this, in turn, usually includes a complex metamorphosis, in which only the first larval stage - nauplius - is common to all crustaceans. But some others, and in some cases all of them, including the first one, may be absent, and then a copy of an adult animal immediately hatches from the fertilized egg, but only a miniature one...
Some edible and harmful species of crustaceans have been known to man since ancient times, but most representatives of this class are known only to specialists. As it turns out, crustacean animals are among the most numerous on our planet. Currently, scientists have described more than 25,000 of their species. Moreover, most species of crustaceans live in the seas and oceans, so they are sometimes figuratively called “sea insects” for their abundance and diversity. However, many species of crustaceans also live in fresh waters and on land. Therefore, they can practically be found in all bodies of water: under ice in the polar regions, and in hot springs with temperatures up to 50 ° C, and in deserts, and at depths of up to 6 km, and on the tops of tropical trees.
Great and economic importance crustaceans. Wherein great importance have crabs, lobsters, crayfish and shrimp, which are directly consumed by humans. But numerous small forms, which float en masse near the surface of reservoirs as part of zooplankton and are often barely visible to the naked eye, form the main link of a whole series food chains. It is these tiny crustaceans that are the link between microscopic planktonic algae and fish, whales and other large game animals. Without small crustaceans that transform plant cells in easily digestible animal feed, the existence of most representatives aquatic fauna would become practically impossible.
Among crustaceans there are many species that are harmful to humans, which in one way or another cause damage to a person’s economy or his health. Thus, boring forms of crustaceans, such as the woodworm, make passages in wooden port structures and other underwater buildings. On the bottoms of ships, sea acorns and barnacles form thick foulings that interfere with navigation. Some species of crabs, crayfish and some other crustaceans are found in the tropics (and Far East Russia) are carriers of human diseases, and other crustaceans, such as wood lice and shield bugs, often harm vegetation, in particular rice crops, or farmed marine species.
The most primitive crustaceans belong to the subclass Gill-footed(Branchiopoda). Daphnia(Daphnia) are representatives of the order Listopods, suborder Cladocera. Daphnia, inhabitants of the water column, are often called water fleas, probably due to their small size and spasmodic mode of movement. Let's place several living specimens of D. magna in a glass jar and observe them. The body of the crustaceans is up to 6 mm long, covered with a bivalve shell, flattened on the sides. On a small head there is a large black spot- the eye, and in the body part the brownish-greenish intestine, clogged with food, is visible.
|
Daphnia (Daphnia magna) |
Daphnias do not remain quiet for a second. The main role in movement is played by the flapping of the long lateral antennas. Daphnia's legs are leaf-shaped, small, do not take any part in movement, but regularly serve for feeding and breathing. The legs are constantly working, making up to 500 strokes per minute. This way they create a current of water carrying algae, bacteria, yeast and oxygen.
Cladocerans also include pelagic crustaceans such as small (less than 1 mm in length) long-nosed bosmina(Bosmina longirostris). It is easily recognized by its long, curved nose - the rostrum - with a tuft of bristles in the middle. An even smaller owner of a brownish spherical shell - Hydorus sphericus(Chydorus sphaericus) - can be found both in the water column and among coastal thickets.
Also widespread copepods(Copepoda) - cyclops and diaptomus, which belong to the subclass Maxillopod(Maxillopoda). Their body consists of a head, articulated thorax and abdomen. The main organs of movement are powerful antennae and pectoral legs bearing swimming setae. The legs work synchronously, like oars. This is where the common name for crustaceans comes from - “copepods”.
|
|
|
|
Diaptomus graciloides, female |
Diaptomus (Eudiaptomus graciloides), male |
Diaptomuses, like daphnia, are completely peaceful animals. In a glass vessel you can easily observe their movement. Diaptomus(Eudiaptomus graciloides) glide smoothly, balancing with outstretched antennae, the length of which is almost equal to the length of the entire body. Having dropped down, they make a sharp stroke with their chest legs and short abdomen and “jump” up. The crustaceans create a current of water carrying food with short second antennae that make several hundred beats per minute. The elongated body of the crustacean is translucent and colorless, they need to be invisible to predators. Female diaptomus often carry a small pouch filled with eggs under their abdomen. Males are easily distinguished by their right antenna with a node in the middle and the complex last pair of legs with long hooked projections. The male uses these devices to hold the female.
They are even more common in fresh waters cyclops, named after the one-eyed hero ancient greek myths. There is only one eye on the head of these crustaceans! The cyclops (Cyclops kolensis) has short antennae; adult females carry their eggs in two bags on the sides of the abdomen. Males hold their partners with both front loop-shaped antennae. Cyclops are distinguished by their fussy, seemingly chaotic movement. They “jump” often and sometimes tumble in the water. The fast and chaotic movement of the cyclops is aimed at achieving two main goals: firstly, not to get caught in the mouth of a fish, and secondly, to have time to grab something edible. Cyclops are by no means vegetarians. If they come across a large algae, they will eat that too, but they still prefer the juveniles of their cladoceran and copepod neighbors and other aquatic small things, for example, ciliates and rotifers.
Lower Crustaceans
Subclass Gill-footed
The most primitive. These small crustaceans have leaf-shaped legs and are used equally for movement and breathing. They also create a current of water that carries food particles to the mouth. Their eggs easily tolerate drying out and wait in the soil for the new rainy season. Artemia is an interesting branchiopod: it can live in salt lakes with a salt concentration of up to 300 g/l, and dies in fresh water after 2-3 days.
Subclass Maxillopods (jaws)
Representatives of the barnacle order are amazing: sea acorns and barnacles. These sea crayfish switched to a sedentary lifestyle in houses made of limestone plates. The larva is a typical nauplius, sinks to the bottom and attaches itself with antennules. The antennules and the entire anterior part of the head turns into an organ of attachment (a long fleshy stalk in sea ducks, or a flat wide sole in sea acorns), the antennae and compound eyes atrophy, the thoracic legs extend into long two-branched “antennae”, driving food to the mouth.
The most primitive crustaceans belong to the subclass Branchiopods. Daphnia are representatives of the order Listopods, suborder Cladocera. Quite often, Daphnia, inhabitants of the water column, are called water fleas, due to their spasmodic method and movement of small sizes. The body of the crustaceans reaches up to 6 mm in length, with a bivalve shell on top, flattened on the sides. A large black spot stands out on the head of the crustacean - the eye; in the body part, a brownish-greenish intestine clogged with food is visible. Daphnias do not remain quiet for a minute. Swings of the long side antennas perform main role in move. Daphnia's legs are small, leaf-shaped, and do not take any part in movement, but they regularly serve for breathing and feeding. The legs are constantly working, making up to 500 strokes per minute. In a similar way, they create a current of water that carries bacteria, algae, yeast and oxygen. The suborder Cladocera also includes pelagic crustaceans such as the small long-nosed bosmina (less than 1 mm in length). It can be recognized by its long, curved nose with a tuft of bristles in the middle. Another, even smaller owner of a brownish shell - Hydorus sphericalis - can be found both in the water column and among coastal thickets. Also widespread are copepods - cyclops and diaptomus, belonging to the subclass Maxillopods. Their body consists of a head, articulated abdomen and chest. Main body movements - legs and powerful antennas. The legs work synchronously, like oars. That's where it went from here common name- "copepods". Diaptomuses are also quite peaceful animals. Diaptomus hover smoothly, balancing with outstretched antennae, the length of which is almost equal to the entire length of the body. Having dropped down, Diaptomus makes a sharp stroke with its legs and small abdomen and “jumps” up. The elongated body of the crustacean is colorless and translucent; they need to remain invisible to predators. Females often carry a small pouch under their abdomen. Males can be recognized by the right antenna with a node in the middle and the complex last pair of legs, with long hooked outgrowths. More often in fresh waters you can find cyclops, named after the one-eyed hero of myths Ancient Greece. There is only one eye on the head of these crustaceans! Cyclops have short antennae. This type characterized by fussy, seemingly chaotic movement. They often "jump" and periodically tumble in the water. The chaotic and fast movement of the cyclops pursues two main goals: not to get caught in the mouth of a fish, and to have time to grab something edible. Cyclops are not vegetarians. They can also eat large algae, but they still prefer the juveniles of their copepods and cladocerans, as well as other aquatic small creatures, for example, rotifers and ciliates.