General characteristics and structure of the Crustacean class.

Crustaceans are mainly marine animals, representatives of a number of species live in fresh waters and on land.
Among crustaceans there are sessile, attached species, there are parasites, but most are free-living.
These animals feed mainly on algae, but there are also predators, corpse eaters.

External structure, parts of the body (for example, the decapod crayfish squad)

The number of body parts is different, but almost all of them have a head, chest and abdomen. Often the parts of the body grow together, forming the cephalothorax, for example, in crayfish, a representative of the order of Decapod crayfish.
The senses are well developed: touch, smell, balance, hearing, vision.
The eyes are compound, faceted, located on the stems.
Cancer has two pairs of antennae. Long antennae (antennae) serve as organs of touch, and short antennae (antennae) serve as organs of smell and touch.
Below the antennae are the mouth organs – modified limbs.
The first pair of modified limbs forms the upper jaws, and the second and third pairs form the lower jaws. With the help of three more pairs of modified limbs – leg-jaws – the cancer directs prey into the mouth.
Five pairs of walking legs are located on the cephalothorax behind the cephalothorax.
The first pair of legs is the largest, ending in highly developed pincers (they serve as organs of attack, defense and food capture).
There are also abdominal legs on the articulated abdomen. On them, females carry eggs (eggs).
Crustaceans breathe with the help of gills, which are protected by the shell of the cephalothorax. The circulatory system is not closed. The saccular heart and the main vessels extending from it are located in the thoracic region on the dorsal side.
The excretory organs are the kidneys, or green glands.
The nervous system of crayfish, like that of other arthropods, is the periopharyngeal nerve ring and the abdominal nerve cord.

Value

Representatives of many species are excellent food for fish and other animals living in or near water – these are small crustaceans: daphnia, cyclops, amphipods.
Many crustaceans are used by humans for food, among them – shrimps, crabs, lobsters, lobsters, crayfish.

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