This article pays attention to various types of worms, in particular flat, round and annular. A special place will be allocated to flatworms. Their various bodies and their activities will be examined. For example, we will analyze how flatworms breathe, examine the structure of excretory and reproductive systems, etc. And also some of their representatives will be considered.
Variety of worms
Worms include groups of multicellular animals in which an elongated body and a skeleton are missing. Habitats are, as a rule, moist soil, the sea and fresh water bodies. In size, they can vary from those that can only be detected under a microscope, to large forms, several meters long. In accordance with the shape of the body allocate: Flat, Round and Annelid worms. All types have three layers of the body. The embryonic layers - ectoderm, endoderm and mesoderm give rise to the development of all their tissues and organs.
The brightest and most famous representatives of flatworms are: planaria, hepatic fluke, pork and bovine tapeworms, echinococcus, schistosome, etc. Known annelids include: earthworm, small-worm worms, leeches and misostomids. Round primitives are represented by all known roundworms, pinworms, rishts, trichinella, etc.
Despite the variety of existing types of worms, their types, structural features, methods of reproduction, nutrition, habitats, etc., there are a considerable number of similarities characteristic of all of them. For example, flatworm breathing, 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 primary invertebrate animals. These creatures belong in a 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, vital processes and physiology of these creatures. They are inhabitants of salt 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 vertebrates and invertebrates. Now about 25,000 species are described, over three thousand species inhabit the territory of the Russian Federation.
The system of organs of flatworms is represented by a number of basic structural components, united by common functional features and by type of structure. The main systems include: respiratory, reproductive, excretory, muscle, nervous and integumentary.
Some representatives of flatworms, for example, planaria, inhabit freshwater bodies of water. Among the ciliary worms, this is the most famous. Parasites include flukes, for example, liver and cat flukes, schistosomes, as well as tape ones (broad tapeworms, bovine and pork tapeworms, echinococci).
Earlier, a series of other taxonomic elements, characterized by worm-shaped forms, the absence of body cavities and considered to be invertebrates, were attributed to the class of ciliary primary whales.
The body shape of any type has a bilaterally symmetrical shape, in which the head and tail ends are slightly flattened at both ends, but in large species, flattening is very pronounced. The system of organs of flatworms for respiration and blood circulation is absent. The cavity in the body does not develop, however, this is true for all representatives, except for tapeworms and flukes on certain life cycles.
The structure of the integument
The breathing of a flat worm is carried out precisely through the surface of the body, because it is associated with the structure of the integument. Outside, the body is covered with one layer of epithelium. Ciliary worms (turbellaria) have an epithelium consisting of cells that carry cilia. Flat parasitic worms, flukes, as well as representatives of monogenes, cestode-like and tapeworms do not possess ciliary epithelium during the main part of their lives. Ciliary cells can be found in larvae. The integuments of the body of these three types are represented in the form of teguments that carry microvilli or chitinous hooks. The owners of the tegument are called representatives of the Neodermata group. About 6/7 of their composite body, flatworms are able to regenerate by regeneration.
Acquaintance with muscles
The muscle tissue of flatworms is represented by a muscular sac, which lies beneath 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 transversely, and the inner ones along the posterior-anterior axis of the body. The external musculature is called the annular layer, and the internal - the longitudinal layer of musculature.
Breathing methods
Now we will try to understand the question of how the breathing of flatworms is carried out? A detailed description of respiratory processes is described only superficially. It is important to know only that the breathing of flatworms is carried out through the cavity of the whole body. It follows from this that the special respiratory organs characteristic of many animals are absent. However, this applies to parasitic forms of worms and free-living species, and endoparasites living in an environment with a small amount of oxygen can breathe in anaerobic way.
The aerobic type of flatworms is breathed by diffusion - interpenetration, for example, of gases, in order to level them throughout the body. Anaerobic glycolysis of endoparasites is a self-sufficient process, which is characterized by the presence of three conditions: the arrival of glucose, the presence of ATP, in almost any quantity and the restoration of the lost supply of NAD.
Introduction to the pharynx and gut
All groups of flatworms are characterized by the presence of a pharynx, which leads to the intestine. The exception is cestode-shaped and tapeworms. This gut opens into the parenchyma, intended for digestion, blindly closes and is connected to the outside world only with the mouth opening. Some large turbellaria have anal pores, however, this is an exception only for some species. Small forms are characterized by a rectum, and large forms (planaria, trematode) can be branched. 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 the planar primary and fourth, it is worth noting that they are characterized by the presence of nerve nodes located in front of the body, as well as there are ganglia of the brain and nerve columns branching from them, which are connected by jumpers. Sensitive organs include individual skin cilia, which are processes of nerve-type cells. There are free-living species that have special pigment-sensitive eyes sensitive to light. Such organs serve as a primitive adaptation to a sense of balance and allow you to see, albeit primitively.
Highlight system
The flat type worms have an excretory system that takes the form of protonephridia. With their help, the process of osmoregulation and metabolism proceeds. The allocation system takes the form of channels that branch and are combined into 1-2 channels. Initially, these are star-type cells, which branch out into the tubules and open a lumen 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. The worm's life-threatening metabolic products are excreted together with fluids through the aforementioned protonephridia, as well as with the help of special parenchyma cells - atrocytes, which play the role of "accumulative kidneys".
Reproduction
Hermaphrodites predominate among flatworms, only some species are dioecious, for example, schistosomatidae. The reproductive system, both male and female, can vary greatly between species in terms of the structural form of the testes and ovary. The same applies to the remaining components of the reproductive system. Certain groups of ciliary worms and all parasite representatives have an ovary divided into 2 parts:
- Germaria - is actually the ovary. Produces eggs that are poor in yolk, but capable of development.
- Vitellarium - sometimes called vitelline, it produces abortive-type eggs, they are rich in yolk.
These composite reproductive systems form complex, or exolecital, eggs. The common membrane may contain one egg or a certain number of yolk balls secreted by the glands of the accessory type.
Conclusion
Summing up the above text, we can draw several conclusions, among which the most significant are: the breathing of flatworms is carried out by the surface of the whole body, predominantly flatworms belong to predators, there is a muscular sac, the cover of the body is represented by the tegument, most relate to hermaphrodites and only a few of them are dioecious.