Business idea - crayfish

Crustaceans are arthropods zhabrodyshaschim arthropods.

The body of crustaceans is the length from 0,5 mm up to 80 cm. It is covered by hitin and the shell consists of head, chest and abdomen. On his head there are two pairs of tangible appendages (antennas and antennul) and three pair of jaws. The chest and abdomen segmented. The number of legs for different groups of crustaceans may vary.

fig.: structure of the river cancer.

The digestive system of shellfish includes chewing stomach, intestines and "liver". Respiratory organs - the gills, located on the legs or on the sides of the body, a some forms of land - falsetraheas. Bodies of the spin (channels, connecting a whole with the external environment). Senses - fasets eyes, stacionists and antennae.
Most crustaceans have separated sexes; barnacles crustaceans, leading a sedentary lifestyle, are hermaphrodites. Fertilization outside (males attached sperm near the genital openings females). As a rule, these animals have been developed with several metamorphosis; their larva is called nauplis.
Crustaceans are the inhabitants of the seas, where they make up the majority of zooplankton and a significant part of the benthos and serve as food for the fish. Live crayfish and in fresh waters, the land-based live only a few - winter weed and some land crabs. Crustaceans feed on bacteria and protozoa, detritus, plants or animals. Meshkogruds, copepods and the barnacle - parasites. Decapods (kamchatka crab, river crayfish, lobsters, shrimps, lobsters) divorced man and are used in food.

Crustaceans occurred or from the extinct trilobite, either directly from the annelid worms. In the fossil condition they are known to kembrium. Modern crustaceans about 30 000 species combined into five divisions (according to other researches - classes) ostracods, barnacles, copepods crayfish and higher cancers.