Roundworms: a brief description of the type

Round worms, or as they are called Nematodes, are organisms with a primary body cavity. They dwell in the most diverse places of the planet - in the seas, fresh water bodies and soil. Some representatives are parasites - they exist at the expense of plant and animal organisms. The most famous human parasites are ascarids and trichinella.

Type Round worms: features of the structure . The title says a lot about the structure of representatives of this type - in the cross-section, they have a round outline. The body is fusiform and narrowed at the ends, you can clearly see the head at the front end. The type of symmetry of the body is bilateral.

As for the size of these organisms, they vary considerably - from microscopic (80 microns) to almost giant (more than 8 meters in whale parasites).

Their body consists of their skin-muscular sac, which is separated from the internal organs by the primary cavity, or pseudo-cell. The skin on top is covered with a dense layer of cuticle, which is produced by the epithelium of the outer covers.

Round worms: the structure of the digestive system . The digestive tract of this group of organisms is through. The oral opening is located at the anterior end of the body and is surrounded by lips and muscle tissue. It leads to a muscular throat, which is used to actively draw food. The food then enters the middle and then into the hindgut. The products of the exchange are taken out through the anus in the females, or into the cloaca in the males.

It is interesting that in some parasitic organisms of this type the digestive tube is transformed and is a small bag without apertures.

Round worms: breathing and excretion . The excretory system of roundworms is pretty. This includes a large unicellular cervical gland. Metabolism products accumulate in the cavity fluid, after which they move through the two longitudinal lateral channels into the gland and are discharged outward. The cervical gland has a separate excretory opening that opens in the abdominal part of the body. Some metabolites, for example ammonia, are discharged directly through the wall of the body.

As for breathing, organisms specially designed for this organ do not exist. Oxygen is absorbed by the intestinal tissues. In the event that you have to live in conditions of oxygen starvation, roundworms can pass to anaerobic type of breathing.

Round worms and their nervous system . The nervous system in these organisms is quite primitive, especially in parasitic forms. The main associative center is represented by the peripheral nervous ganglia, from which two nerve trunks depart.

As for the sense organs, they are represented by papillae, bristles, amphids and other formations. All these are organs of mechanical, chemical and light sensitivity. In parasites of this type , the sense organs are worse developed than in free-living forms.

Round worms: reproduction . Representatives of this type of animals belong to dioecious organisms. At the same time, a fairly noticeable sexual dimorphism is also observed: in the male, the posterior end is bent to the abdominal part of the body.

The sex organs of the female are represented by the ovaries, the uterus and the oviducts. The male has testicles, vas deferens and an ejaculatory duct. The male sperm are inserted into the vagina of the female through the copulatory organ. It is interesting that spermatozoa do not have flagella, they have limited mobility and an amoeboid form.

How are Roundworms different from Flatworms ? In fact, the differences between these two types of animals are quite noticeable. For starters, it's worth mentioning the shape of the body - in cross section. Flat worms have an oblate body. Another significant difference is the primary body cavity, which is absent in representatives of Flatworms. In addition, the Nematode already appears through the digestive system. It should be noted that Flatworms are hermaphrodites.