This article focuses on different types of worms, in particular flatworms, roundworms, and annelids. A special place will be allocated to flatworms. Their various bodies and their activities will be reviewed. For example, we will analyze how flatworms breathe, study the structure of the excretory and reproductive systems, etc. And also some of their representatives will be considered.
Variety of worms
Worms are a group of multicellular animals that have an elongated body and no skeleton. Habitats are usually wet soil, sea and fresh water. In size, they can vary from those that can only be detected with a microscope, to large forms, several meters long. In accordance with the shape of the body, there are: Flat, Round and Annelids. All types have three body layers. Germ layers - ectoderm, endoderm and mesoderm give rise to the development of all their tissues andauthorities.
The brightest and most famous representatives of flatworms: planarian, liver fluke, porcine and bovine tapeworm, echinococcus, schistosome, etc. Known annelids include: earthworm, oligochaete worms, leeches and misostomids. Round protostomes are represented by well-known roundworms, pinworms, guinea worms, trichinella, etc.
Despite the diversity of existing worm species, their types, structural features, methods of reproduction, nutrition, habitats, etc., there are a considerable number of similarities that are characteristic of all of them. For example, the respiration of flatworms, divided into aerobic and anaerobic, depending on the habitat, is also characteristic of the other two types.
Flatworms
Let's start with the general characteristics of worms. Flatworms are invertebrate animals belonging to protostomes. These creatures belong in the taxonomic hierarchy to animals of a multicellular type, having an elongated body shape and the absence of an internal skeleton. Zoology of the type Flatworms is a description of the structure, life processes and physiology of these creatures. They are inhabitants of s alt and fresh water bodies, other representatives can survive in places with high humidity. The remaining classes are engaged in parasitism, living on a variety of animals, including both vertebrates and invertebrates. Approximately 25,000 species have now been described, and more than three thousand species live on the territory of the Russian Federation.
The organ system of flatworms is represented by a number ofthe main structural components, united by common functional features and by type of structure. The main systems include: respiratory, reproductive, excretory, muscular, nervous and integumentary.
Some representatives of flatworms, such as planaria, inhabit fresh water bodies. Among the ciliary worms, this is the most famous. Parasites include flukes, such as liver and cat flukes, schistosomes, and tapeworms (broad tapeworms, bovine and pork tapeworms, echinococci).
Previously, a number of other taxonomic elements were attributed to the class of ciliary protostomes, characterized by worm-like forms, the absence of body cavities and considered invertebrates.
The body shape of any type has a bilaterally symmetrical shape, in which the head and tail ends are pronounced, both ends are slightly flattened, however, in large species, the flattening is strongly pronounced. The organ system of flatworms for respiration and circulation is absent. The body cavity does not develop, but this is true for all representatives, except for tapeworms and flukes in certain life cycles.
The structure of the integument of the body
The respiration of a flatworm is carried out precisely through the surface of the body of the body, because it is associated with the structure of the integument of the body. Outside, the body is covered with a single layer of epithelium. Ciliary worms (turbellaria) have an epithelium consisting of cells that carry cilia. Parasitic flatworms, flukes, as well as representatives of monogeneans, cestodes andtapeworms do not have ciliated epithelium for most of their lives. Cells of the ciliary type may be found in larvae. The body coverings of these three types appear as teguments, which bear microvilli or chitinous hooks. The owners of the tegument are called representatives of the Neodermata group. About 6/7 of their body composition, flatworms are able to regenerate through regeneration.
Meet the muscles
The muscle tissues of flatworms are represented by a muscular sac that lies under the epithelium. It consists of a number of layers of muscle-type cells that are not divided into muscles. However, some differentiation is observed in the areas of the pharynx and reproductive system. The outer part of the cells of the muscle layers are oriented across, and the inner ones along the posterior-anterior axis of the body. The outer musculature is called the annular layer, and the inner one is called the longitudinal musculature layer.
Breathing Methods
Now we will try to analyze the question of how flatworms breathe? A detailed description of the processes of respiration is described only superficially. It is only important to know that flatworms breathe through the entire body cavity. It follows from this that they do not have special respiratory organs characteristic of many animals. However, this applies to parasitic forms of worms and free-living species, and endoparasites living in an environment with a low amount of oxygen can perform anaerobic respiration.
Respiration of flatworms aerobictype is carried out by diffusion - interpenetration, for example, of gases, in order to align them throughout the volume of the body. Anaerobic glycolysis of endoparasites is a process of a self-sufficient type, which is characterized by the presence of three conditions: the arrival of glucose, the presence of ATP, in almost any amount, and the restoration of the lost supply of NAD.
Familiarization with the pharynx and intestines
All groups of flatworms are characterized by the presence of a pharynx that leads to the intestine. The exceptions are cestodes and tapeworms. This intestine opens into the parenchyma intended for digestion, blindly closes and is connected with the outside world only through the mouth opening. Some large turbellarians have anal pores in their presence, however, this is an exception only for some members of the species. Small forms are characterized by a straight intestine, while large ones (planarian, fluke) may have a branched one. The pharynx is located on the surface of the abdomen, often it can be found in the middle or closer to the back of the body. In some groups of worms, the pharynx moves forward.
Features of the nervous system and sensory organs
Characterizing the nervous system of flat protostomes, it is worth noting that they are characterized by the presence of nerve nodes located in front of the body, and there are also ganglia of the brain and nerve columns branching off from them, which are connected by jumpers. The sensitive organs include individual skin cilia, which are processes of nerve-type cells. There are free-living species that have special,pigmented eyes sensitive to light. Such organs serve as a primitive adaptation to the sense of balance and allow you to see, albeit primitively.
Isolation system
Squamous worms have an excretory system that takes the form of protonephridia. With their help, the process of osmoregulation and metabolism proceeds. The selection system takes the form of channels that branch and combine into 1-2 channels. Initially, these are stellate-type cells, which, branching into tubules, open a gap in themselves for the passage of a bundle of flagella. Merging, the tubules form a larger structure and are excreted in the form of excretory pores on the surface of the body. Such excretion systems are called protonephridial. Metabolic products dangerous for the life of the worm are excreted along with the liquids through the aforementioned protonephridia, as well as with the help of special parenchyma cells - atrocytes, which play the role of "accumulative kidneys".
Reproduction
Among flatworms, hermaphrodites predominate, only some species are dioecious, for example, schistosomatidae. The reproductive system, both male and female, can differ greatly between species in terms of the shape of the structure of the testes and ovary. The same applies to other components of the reproductive system. Certain groups of ciliary worms and all representatives of parasites have an ovary divided into 2 parts:
- Germarium - is actually an ovary. Produces eggs, pooron the yolk, but capable of development.
- Vitellaria - sometimes called vitellaria, it produces abortive-type eggs, they are rich in yolk.
These composite reproductive systems form complex or exolecithal eggs. The common shell may contain one egg or a number of yolk balls secreted by adnexal glands.
Conclusion
Summing up the above text, we can make several conclusions, among which the most significant are: the respiration of flatworms is carried out by the surface of the entire body, mainly flatworms are predators, there is a muscular sac, the body cover is represented by a tegument, most are hermaphrodites and only few of them are dioecious.
