Ringworms: a brief description of the type

Ringworms are a fairly large groupinvertebrate organisms. In addition, they are considered the most organized representatives of worms. They dwell mainly in fresh and salt water bodies, as well as in the soil. Some species of tropical leeches have adapted to the terrestrial mode of existence.

Type Ringworms: General

The sizes of representatives of this group fluctuatefrom a few millimeters to six meters. Quite a characteristic feature of such an organism is the presence of segmentation - their body consists of many rings, which explains the name of the type. Outer annularity corresponds to internal segmentation. That is why when wounding or damaging the body, the ringworm loses only a few segments, which soon regenerate.

From the outside, the body is covered with a cuticle that is notis reset. From it grow chitinous setae - another characteristic feature of this group of animals. Some representatives on the segments may have parapodia - rather primitive limbs, which in some cases are equipped with sensitive bristles or gills.

Ringworms: features of the structure of internal organs

For representatives of this type is characteristicthe presence of a secondary body cavity - the coelom. This cavity is filled with a specific liquid, due to which the normal indices of the internal environment of the organism are maintained.

There is a skin-muscular sac, which consists of balls of epithelium, as well as muscles, grouped into annular and longitudinal groups.

Digestive system through, begins with the mouthand ends with an anal opening. Ringworms have three sections of the intestine - anterior, middle and posterior. In some species primitive salivary glands are formed.

Respiration of the body is through skincovers. The only exceptions are certain marine species of animals, in which the gills are located on the parapodia. As for the circulatory system, it is, as a rule, closed. It consists of the abdominal and dorsal aorta, which are connected together by annular vessels. The hearts of these organisms do not exist - blood movement is provided by contraction of the dorsal aorta. The blood of roundworms can contain a wide variety of respiratory pigments.

The nervous system is still quite simple. At the anterior end of the body is a large nerve ganglion, which functions as a brain. From it departs a neural chain, which in each segment of the body forms a small ganglion - a cluster of neurons. The sense organs are represented by eyes, organs of chemical sensitivity, and also by mechanoreceptors, which are distributed throughout the body of the worm.

Ringworms: Features of reproduction and development

The organisms of this group can be eitherboth sexes, and hermaphrodites (they are much less common). For example, a earthworm has a hermaphroditic reproductive system, but two individuals are required for fertilization. It can occur both in the external environment and by introducing spermatozoa into the internal channels of the female.

It is also interesting that the ringworms withpronounced segmentation have a tendency to rapid and intensive regeneration. Due to this, for some species asexual reproduction is characteristic. The development of organisms is direct, without metamorphosis.

It should be noted that the role of annelidsquite weighty. For example, the well-known earthworm is responsible for the aeration of the soil. This group includes leeches, which are often used in modern medicine. A special value is possessed by hirudin, developed by a leech, as it dilutes blood and is used in the fight against thrombosis and other dangerous diseases.