Table of contents:
- How are annelids arranged?
- Learn more about the vital systems of the annelid body
- How do annelids feel the external environment?
- How do ringlets reproduce?
- Features that characterize all rings, regardless of their types
- What lifestyle do the rings adhere to?
Last updated 3 July 2019 at 04:29 PM
Reading time: 6 minutes
The annelid worms are a very large group of invertebrates, the type belongs to the sub-kingdom of Eumtazoi and the kingdom of Animals. The number of subspecies today is, according to inaccurate estimates, 12,000 - 18,000 pieces.
The rich variety of subspecies is determined by a large number of subtypes: various species are combined into large groups - leeches (number - about 400 species), polychaete (approximately 7000 species), small-bristled, misostomids.
The origin of the type traces its history to the evolution of mollusks and arthropods, annelids can indeed be called ancient creatures. Today there are annelids, round worms and flatworms.
- 1 How are annelids arranged?
- 2 In more detail about the vital systems of the body annelids
- 3 How do annelids feel the environment?
- 4 How do rings reproduce?
- 5 Features characterizing all rings, regardless of their types
6 What lifestyle do the rings adhere to?
6.1 Similar articles
How are annelids arranged?
Worms, both common and annelids, are the oldest inhabitants of the planet; for thousands of years they have practically not changed their appearance.
A distinctive feature of their body structure is the segments (or segments) that make up the entire body. The minimum worm length is 0.25 mm, the maximum is 3 m.
The length directly depends on the number of segments, their number can be equal to 2-400 pieces. Each of the segments forms a complete unit and has strict sets of the same structural elements. The whole body is enclosed in a skin-muscle sac that covers the entire body of the worm.
The general structure of annelids includes:
- head lobe (scientifically "prostomium")
- multi-segment trunk
- anal opening at the end of the body
The musculocutaneous sac as a part of the body has several sections. Ringworms and their structure are unusually constant overlapping fragments. In general, there are two bags in the body of the worm: the outer one that envelops the entire body, like skin, and the inner one, lining the surface under the organs.
Movement in the body is made due to the contraction of blood and nerve vessels: this explains the reason for the pulsating nature of movements. In the intestines of the worm there are special muscles, they are responsible for the digestion of food and its subsequent alienation.
The higher development of the circulatory system speaks of the evolutionary superiority of annelids over their historical ancestors, mollusks and limbs (it is from these creatures that annelids originate).
The innovation is that their circulatory system is closed. The aforementioned blood vessels in the abdominal and dorsal cavities carry blood from one segment to another.
It is through the flow of blood that movement is made. So, the activity of the body and its ability to move and navigate the terrain completely depend on the functioning of the circulatory system.
If we talk about external organs of movement, then parapodia will be responsible for them. This scientific term refers to the bivalve fins that grow on the outer sides of the worm.
When adhering to the surface (most often soil), parapodia provide repulsion of the annelids and advance forward or sideways. The mode of movement does not affect the differences between sexually and non-sexually reproducing worms.
Learn more about the vital systems of the annelid body
The food system is very diverse, because has a very segmented structure. The anterior intestine is divided into 3 sections and includes the mouth, pharynx, esophagus, as well as the goiter and stomach. The hind gut ends with the anus.
The respiratory system is very developed and is formed in the form of gills, which are quite invisible on the surface of the cover. These gills have a completely different look: their structure can be feather-like, leaf-like, or even bushy.
The excretory system of worms has a structure adapted to the structure of their body. This means that metanephridia, paired tubular organs with a special excretory tubule, are duplicated in each of the body segments.
The withdrawal of the cavity fluid is performed through the opening of all identical tubules and subsequent engagement.
The anal opening is not directly on the integument of the body. When the cavity fluid is alienated, a special tubule opens outward, the supply occurs precisely through it. Then the hole is closed, and the integuments regain their integrity.
Most species of annelids are dioecious, but this is not necessarily the case. In species whose origin occurred historically less long ago, hermaphroditism is observed, which developed a second time. This means that individuals can also be bisexual.
How do annelids feel the external environment?
The type of nervous system is ganglian. This means that in the body of an animal, the nervous system is arranged in such a way that all nerve vessels belong to one sensitive nerve node. He coordinates the incoming information, and the system of nerve nodes is the central nervous system.
The elements of the nervous system of the ring are well-knit and interconnected, the sense organs, as methods of analyzing the external environment, are located on the head part, the ganglia, as part of the abdominal chain, line the abdominal cavity and are connected in pairs.
There are two important centers in the head lobe: the supraopharyngeal and subopharyngeal ganglia, in turn, they are formed into a common node. The organs of vision, touch, balance are drawn to the supraopharyngeal node in special ways.
The supraopharyngeal and subopharyngeal nodes are connected by columns, so messages are transmitted between the organs, and a nerve ring appears, which communicates with the abdominal region.
The sense organs are located on the head part of the body, it is this area that turns out to be the most sensitive. In rings, there is a surprisingly good development of organs for the perception of environments and conditions of the external world.
They can see, feel the pressure on the surface of their covers, and also analyze the chemical composition of the soil in which they live.
When moving, they maintain balance, this feeling is especially sensitive so that ringworms can feel the position of their body in the soil, as a closed solid system.
Their balance also helps them to stay on the surface of the earth, especially, this is true when any aggressors in the form of animals or people take worms to the surface.
How do ringlets reproduce?
Given the sex characteristics of various species (worms are dioecious or bisexual), in general, the reproduction of annelids can take place in two ways:
If we are talking about asexual reproduction, then most often it is budding, or division into parts. The worm is simply split into pieces, any fallen tail end is able to grow its own head lobe with its organ system.
So, worms multiply and increase their own chances of survival. Even if the mother is divided into two parts or even more, none of them will die, each will grow the missing part.
The division of one body into several, as a way of reproduction, is quite common, especially in species that live in the soil. Budding is observed much less frequently, except perhaps in sillids (budding can occur on the entire surface of the integument of this species).
The asexual mode of reproduction in earthy annelids should be regarded as a special mechanism of adaptation to the living conditions in their environment. A worm living in the outer layers of the soil can always be attacked by a bird or a person.
The defense mechanism assumes the impossibility of destroying the body by crushing. For a worm to really die, it needs to be crushed, not cut.
The sexual mode of annelids during reproduction is traditional for species living in water. Females and males mark the products of their reproductive systems into the water, for example, external fertilization is performed (annelids always reproduce in the external environment, not inside their bodies).
The fry gradually ripen. Their appearance can sometimes copy the appearance of an adult, but this condition is not necessary: the appearance of an immature and an adult worm can be radically different and not even resemble each other's shapes.
As for hermaphrodites, they undergo internal cross-fertilization. Male reproductive organs are presented in the form of testes, which are in seminal capsules, which, in turn, are placed in special bags. The female reproductive organs include a pair of ovaries, a pair of oviducts, and egg sacs.
The development of new individuals occurs outside the cell, the larval stage is bypassed. Fertilized female cells continue their division and development, being suspended from a girdle near the egg cocoon. In leeches, this cocoon is of fundamental importance when growing immature worms: it is from it that nutritive resources are drawn.
Features that characterize all rings, regardless of their types
All annelids have similar properties, and their common characteristic is an extremely important system of knowledge for assessing the evolutionary development of other species.
Ringworms are a special type of organization of biological life; their body structure is characterized by an annular, annular type of segmental body structure.
It is for this reason that the following properties, inherent only in their type, will become distinctive; other species, types and kingdoms may have only some common elements with them, but not in any way an identical paradigm of laws.
So, annelids are characterized by the following:
- Three layers. In embryos, the development of ectoderm, endoderm and mesoderm is observed at once.
- The presence of a special coelomic body cavity lining the organs and viscera. The whole is filled with a special coelomic fluid.
- The presence of a skin-muscle sac, due to which the motor function is produced and the functioning of the nervous, circulatory and digestive systems is ensured.
- Two-sided symmetry. Formally, you can draw an axis along the center of the body and see mirror symmetry with a repetition of the structure and various vital systems.
- The emergence of simple limbs that facilitate movement.
- Development of all major vital systems within one single organism: digestive, excretory, nervous, respiratory, sexual.
- Separated cavity
What lifestyle do the rings adhere to?
Ringlets hardly sleep and can function both day and night. Their lifestyle is irregular, they are especially active during rain or when an increased amount of moisture is concentrated in the soil (this tendency is noticeable in species called earthworms).
The annelids live in all possible environments: in salt seas, fresh water bodies, on land. Among the worms, there are both those who get their food on their own, and those who are scavengers (here it is worth highlighting the common scavengers, bloodsucking, etc. related to them).
You can often find real predators (the best example: leeches, they were attributed to the most dangerous species in this type, because they pose a potential threat to humans). However, most of the worms are very peaceful and feed on the soil, or rather, process it. Worms can reproduce both year-round and only in a certain season.
The importance of worms in maintaining a healthy soil condition has always been key, because due to intensive movement in the strata, the necessary oxygen and water are carried into the ground.
The enrichment of the composition of the soil occurs due to the fact that the worm absorbs the earth, passes it through its systems and processes it with enzymes, and then brings the soil outside, captures a new portion.
So, there is a constant renewal of earth resources, the existence of the rest of the biological world directly depends on the existence of worms.