Roundworms, or as they are also called Nematodes, are organisms with a primary body cavity. They live in the most diverse places on the planet - in the seas, fresh water and soil. Some representatives are parasites - they exist due to plant and animal organisms. The most famous human parasites are roundworms and trichinella.
Type Roundworms: structural features . The name says a lot about the structure of representatives of this type - in cross section they have a round shape. Their body is spindle-shaped and narrowed at the ends, you can clearly see the head at the front end. The type of body symmetry is bilateral.
As for the size of these organisms, they vary significantly - from microscopic (80 microns) to almost gigantic (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-target. The skin on top is covered with a dense layer of cuticle, which is produced by the epithelium of the external integument.
Roundworms: the structure of the digestive system . The digestive tract of this group of organisms is through. The mouth opening is located on the front end of the body and is surrounded by lips and muscle tissue. It leads to the muscular pharynx, which is used to actively suck in food. The food then goes into the middle, and then into the hind gut. The metabolic products are excreted through the anus in females, or into the cloaca in males.
Interestingly, in some parasitic organisms of this type, the digestive tube is transformed and is a small bag without holes.
Roundworms: breathing and excretion . The excretory system of roundworms is pretty. This includes the large unicellular cervical gland. Metabolism products accumulate in the abdominal fluid, after which they move into the gland along two longitudinal lateral channels and out. The cervical gland has a separate excretory opening, which opens in the abdominal part of the body. Some metabolites, such as ammonia, are released directly through the body wall.
As for breathing, organisms do not have specially designed organs for this. Oxygen is absorbed by the intestinal tissues. In the event that you have to live in conditions of oxygen starvation, roundworms can switch to anaerobic type of respiration.
Roundworms 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 near-pharyngeal nerve ganglion, from which two nerve trunks depart.
As for the sensory organs, they are represented by papillomas, setae, amphids, and other formations. All these are organs of mechanical, chemical and light sensitivity. In parasites of this type , sensory organs are less developed than in free-living forms.
Roundworms: reproduction . Representatives of this type of animal belong to dioecious organisms. At the same time, a rather noticeable sexual dimorphism is observed - in the male, the rear end is bent to the abdominal part of the body.
The female genitals are represented by the ovaries, uterus and oviducts. The male has testes, vas deferens and the ejaculatory canal. Male sperm are introduced into the vagina of the female through the copulative organ. Interestingly, sperm have no flagella, have limited motility and an amoeboid form.
How are Roundworms different from Flatworms ? In fact, the differences between these two types of animals are quite noticeable. To begin with, it is worth mentioning the shape of the body - in cross section Flat worms have a flattened body. Another significant difference is the primary body cavity, which is absent in representatives of Flatworms. In addition, Nematodes already have a through digestive system. It is worth noting that Flatworms are hermaphrodites.