Type Flatworms consist of non-parasitic and parasitic forms. At the same time, free-living organisms are combined into one class, and those that live at the expense of other organisms - into six. Representatives of the Ciliary class (planaria, turbellaria) live in water bodies, most often they are predators.
Parasitic flatworms live in the body of animals and humans. Data
Organisms are well adapted to such living conditions, because they have suckers that attach to the walls of the internal organs of the host, and a jointed body with an ever-increasing number of segments. They are characterized by the absence of a digestive system (except for the Flukes class), nutrients are absorbed through special outgrowths of the body; anaerobic respiration (they breathe in a virtually anoxic environment), as well as rapid reproduction (they are hermaphrodites).
All these featuresallow these organisms to permanently settle in the body of the host and exist at his expense. These helminths include: liver fluke, remenets, cat fluke, tapeworm, echinococcus, etc. A person can become infected with them if they eat raw or poorly processed cattle meat, pork, fish.
Type Flatworms unites organisms that have similar features of both external and internal structure. They are barren animals, have an elongated, flattened body from top to bottom, i.e. it is flat or almost flat. Also, it is in them that bilateral symmetry first appears and in the process of ontogenesis three germ layers are laid - ecto-, meso- and endoderm - from which internal organs are subsequently formed. Type Flatworms also characterizes the presence of a skin-muscular sac, which is a combination of the epithelium and the muscle fibers located under it. This allows them to move like a worm.
The digestive system of free-living forms has a primitive structure and consists of the foregut or pharynx, the midgut, which ends blindly. In helminths, this organ system is reduced.
The nervous system of flatworms is represented by a paired cerebral ganglion and nerve trunks that extend from it and are connected by ring bridges. Two longitudinal abdominal trunks become strongly developed.
There are no circulatory and respiratory systems. Representatives of the Ciliary class breathe with the epithelium that covers them.body outside.
Organs of excretion - protonephridia. They consist of a system of tubules that end in a stellate cell with cilia. The excretion of metabolic products into the external environment occurs through special excretory openings.
The reproductive system is hermaphroditic and most often it is a system of ducts that are needed to remove the reproductive products, and a copulatory organ for internal fertilization.
Thus, the type Flatworms are basically parasitic forms (helminths) that have been able to adapt and adapt to their lifestyle.
