known about twelve and a half thousand species of flatworms.All these are divided into three classes.The first class includes turbellarians (ciliary), the second - flukes, the third - Belt flatworms.
They appeared around the time of the Proterozoic.It was the first triple-animals with bilateral symmetry.As a rule, flatworms predators feed on protozoa.Live animals in water.
flat parasitic worms appeared a little later.They are characterized by changes in individual organs of digestion and feelings.Dwell these flatworms in the animal body, human body or fish.They cause poisoning, severe illness, exhaustion and severe damage to the blood system.The medical importance of the flatworms was first formulated by Scriabin.Academician developed a whole science - Helminthology.A distinctive feature is the presence of parasitic species of different devices (idioadaptatsy).Thus, in these animals revealed sucker hooks.They are characterized by large and fertility.
Ciliated flatworms
This class consists of about three thousand species.They live mostly in fresh and marine waters.Occasionally they can be found in the soil.
One of the representatives Turbellaria is milk (white) planar.She inhabits in fresh water.Her body has a leaf-shaped, pointy tail and advanced front end.Planarians length of about one or two centimeters.
Reproduction of this kind is carried out both asexual and sexual means.In the first case the cross separation of the body into two parts.
hermaphroditic reproductive system and arranged quite difficult.Fertilization cross.
Flukes
This class is represented by parasitic flatworms forms.They live in the bodies of humans and vertebrate animals and are found in invertebrates.There are about four thousand species of these worms.
One representative - liver fluke.The size of its leaf-shaped body approximately three - five centimeters.Adults live in the bile ducts of the liver, gall bladder in humans and herbivores.On the ventral side and front of his body is abdominal and oral sucker.With the help of these devices manage flukes held in the host body.It should be noted that these creatures rather poorly developed sense organs.Just floating in the water larvae have eyes.
Flukes are a very prolific species.From one individual within weeks can go up to a million eggs.Their further development is carried out only in water.The reservoir formed by the larvae from the eggs that have to fall into the intermediate host.
Asexual division occurs in the larval body of the mollusk (intermediate host).As a result of this breeding produced a whole generation of larvae whose structure resembles the structure of adults.After that they go out of clam body and settle in coastal seaweed.Formed cysts.Within these larvae can survive a certain time.Together with food or water, the parasites penetrate the human or animal body.
Liver flukes - hermaphrodites.Sexual reproduction is carried out in a final body of the host.
Tapeworms
This class has about three thousand species of parasitic forms.Practically all live only in the intestine of man and different vertebrates.
Tapeworms have ribbonlike body consisting of the cervix (the portion in which the immature bud segments), and the head segments, each of which is repeated androgynous reproductive system.Mature segments are located in the rear area of the body and filled with fertilized eggs.
Tapeworms can have a length of 0.5 millimeters to ten meters.
class representative is a bovine tapeworm.Its growth comes from the cervix.In adult bovine tapeworm parasite in the small intestine in a human body attached to the wall with four suction cups.
