Bivalves (class elasmobranch) - usually slow-moving or immobile animals.They live at the bottom of reservoirs.Known today molluscs are presented in an amount of more than fifteen thousand.Most of them inhabit the sea, less - fresh water.

Bivalves have dvustoronnesimmetrichnoe body.It consists of the legs and torso, the head is reduced (reduced).Typically, the wedge-shaped foot.In moving molluscs it can be put out of the shell, to dig into the ground at the bottom of the pond, pulling all of the animal itself.In specimens affixed to the bottom or lying thereon, a leg is usually reduced to a lesser or greater extent.

Cover bivalves rich in various glands.They secrete mucus and other substances.So, for example, to cover kamnetochtsev legs are glands that secrete acid capable of destroying lime.This allows the animal to freely penetrate into the limestone cliffs.Mussels and zebra mussel have glands that secrete byssus.This material was solidified in water in the form of fine strands by means of which the bivalves are strongly fixed on the substrate.

mantle cavity bounded by two folds that hang on the sides.Inside, there are gills.The mantle cavity is opened and the rectum, genital tract and kidney ducts.The water enters through the gill siphon is removed through the cloacal siphon, which formed the rear edge of the mantle.

Sink animals formed by two wings that are connected by an elastic band on the top or lock - teeth that are located along the top edge of the wings.The majority of the class sash are the same size.However, in some species, lying on the bottom, and they are different in size and shape.

Disclosure leaflets carried by the action of connecting the cords, which is endowed with elastic properties.Convergence also triggered a reduction zapirateley.These powerful muscles connect the two flaps.The increase is due to the shell gland secretions that are in the underlying mantle.In winter, almost no clams grow.As a result, the wings are formed one-year band.They can set the number of the age of the animal.

The nervous system is formed of three pairs of ganglia.One is located in the rear part of the body, the second - in the leg, and the third - on the pharynx.Commissure - the nerve strands - connect all the nodes.

circulatory system consists of shellfish vessels and the heart.At present only one heart ventricle, atrial few.Their number corresponds to the number of gills due to the fact that each of them is represented vasodilatation, which depart from the respiratory system.The heart is located on the dorsal side of the body.

bivalves quite poorly developed sense organs.Sensory cells are scattered in different parts of the body.In the gills are organs Chemical Senses - osfradii.At the foot of statocysts located.This is the body balance.Some representatives of the shellfish distinguished by the presence of numerous holes on the edges of the mantle.

Roth is located above the base of the legs at the front of the torso.On both sides there are two blades.They cover the ciliated epithelium - it cilia customize food particles to the mouth.Esophagus short.It is connected with a small stomach which opens hepatic ducts.From the stomach moves intestine.It forms several loops, climbs to the dorsal side, passes through the ventricle and the pericardial sac and back ends in cloacal siphon.

Shellfish are widely used in human economic activity.Many, such as scallops, oysters, mussels, eaten.