Type Flat worms, features of external and internal structure

The type of flatworm consists of nonparasitic and parasitic forms. In this case, free-living organisms are united in one class, and those that live at the expense of other organisms are six. Representatives of the class Cilia (planaria, turbellaria) live in water bodies, most often predators.

Parasitic flatworms live in the body of animals and humans. Data Organisms are well adapted to such conditions of life, since they have suckers that attach to the walls of the internal organs of the host, and an articulate body with an ever-increasing number of segments. They are characterized by the absence of the digestive system (except for the class of flukes), nutrients are absorbed through special outgrowths of the body; Anaerobic respiration (they breathe in a practically anoxic environment), as well as rapid multiplication (they are hermaphrodites).

All these features allow these organisms to permanently reside in the host's body and exist at his expense. These helminths include: hepatic trematode, remenets, cat fluke, pork thistle, echinococcus, etc. They can be infected by eating raw or poorly processed meat of cattle, pork, fish.

Type Flatworms unites organisms that have similar features of both external and internal structure. They are asexual animals, they have an elongated, flattened body from above, that is, it is flat or almost flat. Also, they have a bilateral symmetry for the first time and in the process of ontogeny, three embryonic sheets are laid-ecto-, meso- and endoderm - from which internal organs are subsequently formed. Type Flat worms also characterize the presence of a skin-muscular sac, which is a collection of epithelium and underlying muscle fibers. This allows them to "wormlike" move.

The digestive system in free-living forms has a primitive structure and consists of the anterior colon or pharynx, the mid-gut, which ends blindly. In helminths this system of organs is reduced.

The nervous system of flat worms is represented by a pair of cerebral ganglions and nerve trunks that branch away from it and are connected by circular bridges. Strongly developed are two longitudinal abdominal trunks.

There is no blood and respiratory system. Breathable representatives of the class of the Ciliated epithelium, which covered their body from the outside.

The organs of excretion are protonephridia. They consist of a system of tubules that end with a star cage with cilia. The excretion of metabolic products into the external environment occurs through special excretory holes.

The reproductive system is hermaphroditic and most often represents a system of ducts that are necessary for the excretion of sexual products, and a copulatory organ for internal fertilization.

Thus, the type of Flat Worms is basically parasitic forms (helminths) that have been able to adapt and adapt to their lifestyle.