Let's start the description with a little wince. worms. What can we do if such trump cards are available in the thick “deck” of the natural diversity of life forms.
I write “trump cards” not only because “ worms". The evolution of multicellularity from two-layered cells led to much more advanced forms of organisms with a three-layered body structure. And then nature had to tinker for a long time, creating not just one, but entire ones.
Somehow it even becomes a shame for all mammals, which represent only a separate class of organisms in the type of chordates. And here, “some kind of worms” - and whole three types: flatworms, roundworms and annelids.
Well, let's start everything in order, so:
……………… Type Flatworms (three-layered)
…………………………………. K l . A. With. With. s
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.. Ciliary worms……………………….. Flukes……………………….. Tapeworms
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White planaria…. Liver fluke …… …………… Bovine tapeworm ___________________________________________________________________________________
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More than 15 thousand species
Habitat: marine and fresh water bodies, wet soil, human and animal bodies.
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Structure: bilaterally symmetrical
. For the first time, embryos develop third
germ layer –
mesoderm, from which parenchymal cells and the muscular system develop. Body flattened.
………..
Body coverings and muscular system: skin-muscular sac - made of single-layer epithelium (maybe be with eyelashes) and three layers smooth muscles (circular, longitudinal and oblique).
Movement: contraction of muscles (flukes, tapeworms) or movement of cilia andmuscles (cilia worms).
Body cavity: absent , internal organs are located inparenchyma.
Digestive system:has two sections - anterior (mouth, pharynx) and middle (branches intestines). The intestine is closed, no anal opening and food residues are removed through the mouth. In tapeworms digestive systemabsent- absorption of food by all cells of the body. As you remember, this is one of their forms biological progress —.
Excretory system: appears for the first time , formed by a system of tubules. One end begins in the parenchyma stellate cell with a bunch of cilia, and the other flows into excretory duct. Channels are combined into one or two common channels ending excretory pores. Elementary the unit of the system isprotonephridia.
Nervous system:from suprapharyngeal ganglia(ganglia) and longitudinal nerves trunks, related crossbars(ladder type).
Sense organs: touch And chemosensitive cells. Free-living animals have organsvision And balance.…………..
Reproductive system: To usually hermaphrodites.Men'sreproductive system: testes, vas deferens, ejaculatory duct and copulatory organ. Women'sreproductive system: ovary, oviduct, uterus, zheltochniki.
1. Appearance of the third germ layer -mesoderm.
2. The appearance of the excretory system - protonephridia.
3. Emergence of the nervous system ladder type.
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All worms can be divided into three types (flat, annelid, round), each of which has its own characteristic features. This type refers to invertebrate animals that lack a body cavity and have bilateral symmetry.
Patients who want to get rid of helminths often ask for natural remedies with the least side effects. In such cases, I recommend this remedy.
The main signs of the type of flatworms
- digestive;
- nervous;
- sexual;
- excretory
This type has several systems and even the rudiments of organs
Circulatory system
Not present, but the function of blood is performed by the parenchyma, consisting of connective cells. It is she who transports nutrients in the body.
Digestive system
Quite simplified, consists of the pharynx and intestines.
The pharynx is powerful and can:
- suck in;
- twist and envelop its victim.
The intestine consists of two sections - anterior and middle, most often branched. It has a closed structure, so that all undigested waste exits through the mouth. The mouth opening is located closer to the middle of the worm's body.
Free worms are mostly predators and they even have a peculiar device for capturing prey. This system is not observed in all classes; more primitive worms do not have it. For example, tapeworms feed on the entire surface.
Excretory system
The excretory system is quite large and consists of many tubules that unite and lead to excretory pores.
The parenchyma contains special cells that drive harmful substances into the tubules. For humans, these excretory products are very dangerous and toxic, along with poison.
§ 1 Habitats and external structure of flatworms
Type Flatworms have about 15 thousand species of animals. Flatworms are found in all habitats: aquatic, soil, land-air and organic. Their body sizes vary from half a millimeter to 15 meters. However, despite such diversity of species, all representatives of this type have a number of common characteristics.
All representatives of Flatworms are multicellular animals and have bilateral body symmetry. Let's remember what symmetry is. Symmetry in biology is the regular arrangement of identical parts of the body relative to the center, which is called the axis of symmetry. Bilateral symmetry means that one side of an animal's body is a mirror image of the other side.
Important feature external structure Representatives of this type of animal also have a flattened top and bottom body shape. On the outside, the body of flatworms is covered with only one layer of epithelium, under which there are 3 layers of muscles. The combination of skin and muscles of worms is usually called the skin-muscle sac.
§ 2 Internal structure of flatworms
Talking about internal structure this type of animal, it must be remembered that the circulatory and respiratory system none. They are characterized by aerobic or anaerobic respiration. Oxygen enters the body through the entire surface of the body.
The digestive system of flatworms consists of a mouth, pharynx and a highly branched intestine. However, the hindgut and anus are absent, so undigested food remains are eliminated through the mouth.
The work of the excretory system is aimed at removing excess water and some metabolic products from the body. In Flatworms, it is represented by a whole network of branched tubules, which are located along the entire body, uniting into 1 or 2 excretory canals; they open at the posterior end of the body.
A pair of suprapharyngeal nerve ganglia and longitudinal nerve trunks, connected by cords, form nervous system. Among the sense organs, Flatworms have light-sensitive eyes, special balance organs, and tactile cells.
Most species of Flatworms are hermaphrodites. Hermaphrodites are animals whose bodies contain both male and female reproductive organs. Despite this, 2 individuals participate in the fertilization process.
§ 3 Taxonomy of Flatworms
The phylum Flatworms are divided into 3 main Classes, namely: Class Ciliated worms, Class Flukes and Class Tapeworms.
The class Ciliated worms includes about 3.5 thousand species of animals. Most ciliated worms are free-living, i.e. they live in any habitat, with the exception of organisms. Their skin is covered with cilia, which give this Class its name. Due to muscle contraction, the cilia move, thereby moving the body in space. The most famous representatives of the Class Ciliated worms are: Planaria milky, Planaria black and Many-eyed.
List of used literature:
- Konstantinov V.M. Lesson planning for the textbook “Biology. Animals" for grade 7, Konstantinov V.M., Babenko V.G., Kumchenko V.S. / Konstantinov V.M. - M.: Ventana-Graf, 2005. - 304 p.
- World Encyclopedia: Biology/ Ch. ed. M.V. Adamczyk: Ch. scientific Ed. V.V. Adamchik: Mn.: Modern writer, 2004. – 832 p.
- Iontseva A.Yu. Biology in diagrams and tables / A.Yu. Iontseva, A.V. Torgalov. – M.: Eksmo, 2014. – 352 p.
- Sadovnichenko Yu.A. Biology / Yu.A. Sadovnichenko. – M.: Eksmo, 2013. – 512 p.
- Biology: a guide for applicants to universities: In 2 volumes. T.1. – 2nd ed., rev. and additional – M.: RIA “New Wave”: Publisher Umerenkov, 2012. – 512 p.
Images used:
Brief description
Habitat and appearance |
Dimensions 10-15 mm, leaf-shaped, live in ponds and low-flowing reservoirs |
Body cover and skin-muscle bag |
The body is covered with single-layer (ciliated) epithelium. The superficial muscle layer is circular, the inner layer is longitudinal and diagonal. There are dorso-abdominal muscles |
Body cavity |
There is no body cavity. Inside there is spongy tissue - parenchyma |
Digestive system |
Consists of the anterior section (pharynx) and the middle section, which looks like highly branched trunks ending blindly |
excretorysystem |
Protonephridia |
Nervous system |
The cerebral ganglion and the nerve trunks coming from it |
Sense organs |
Tactile cells. One or more pairs of eyes. Some species have balance organs |
Respiratory organs |
No. Oxygen is supplied through the entire surface of the body |
Reproduction |
Hermaphrodites. Fertilization is internal, but cross-fertilization - two individuals are needed |
Typical representatives of eyelash worms are planarians(Fig. 1).
Rice. 1.Morphology flatworms using the example of milk planaria. A - appearance of planaria; B, C - internal organs (diagrams); D - part of a cross section through the body of a milk planaria; D - terminal cell of the protonephridial excretory system: 1 - oral opening; 2 - pharynx; 3 - intestines; 4 - protonephridia; 5 - left lateral nerve trunk; 6 - head nerve ganglion; 7 - peephole; 8 - ciliated epithelium; 9 - circular muscles; 10 - oblique muscles; 11 - longitudinal muscles; 12 - dorsoventral muscles; 13 - parenchyma cells; 14 - cells forming rhabdites; 15 - rhabdites; 16 - unicellular gland; 17 - a bunch of eyelashes (flickering flame); 18 - cell nucleus
General characteristics
Appearance and covers . The body of ciliated worms is elongated, leaf-shaped. Dimensions vary from a few millimeters to several centimeters. The body is colorless or white. Most often, eyelash worms are colored various colors grains pigment, embedded in the skin.
Body covered single-layer ciliated epithelium. In the integument there are skin glands, scattered throughout the body or collected in complexes. Of interest are the types of skin glands - rhabditis cells, which contain light-refracting rods Rhabdites. They lie perpendicular to the surface of the body. When an animal is irritated, the rhabdites are thrown out and swell greatly. As a result, mucus forms on the surface of the worm, possibly playing a protective role.
Skin-muscle bag . Under the epithelium is basement membrane, which serves to give the body a certain shape and to attach muscles. The combination of muscles and epithelium forms a single complex - skin-muscle sac. The muscular system consists of several layers smooth muscle fibers. Most superficially located circular muscles, somewhat deeper - longitudinal and the deepest - diagonal muscle fibers. Except listed types muscle fibers are characteristic of ciliated worms dorso-abdominal, or dorsoventral, muscles. These are bundles of fibers running from the dorsal side of the body to the ventral side.
The movement is carried out due to the beating of the cilia (in small forms) or the contraction of the skin-muscular sac (in large representatives).
Clearly expressed body cavities ciliated worms do not. All spaces between organs are filled parenchyma- loose connective tissue. Small spaces between the parenchyma cells are filled with aqueous fluid, due to which products can be transferred from the intestines to the internal organs and metabolic products can be transferred to the excretory system. In addition, parenchyma can be considered as supporting tissue.
Digestive system eyelash worms blindly closed. Mouth also serves for swallowing food, and for throwing out undigested food debris. The mouth is usually located on the ventral side of the body and leads into throat. In some large ciliated worms, such as the freshwater planaria, the mouth opening opens into pharyngeal pocket, in which it is located muscular throat, capable of stretching and protruding out through the mouth. Midgut in small forms of ciliated worms it is canals branching in all directions, and large forms intestines presented three branches: one front, going to the anterior end of the body, and two rear, running along the sides to the rear end of the body.
Main feature nervous system ciliated worms compared to coelenterates is concentration of nerve elements at the anterior end of the body with the formation of a double node - the cerebral ganglion which becomes coordinating center of the whole body. They depart from the ganglion longitudinal nerve trunks, connected by transverse ring jumpers.
Sense organs in ciliated worms they are relatively well developed. Organ of touch All skin serves. In some species, the function of touch is performed by small paired tentacles at the anterior end of the body. Balance sense organs represented by closed sacs - statocysts, with hearing stones inside. Organs of vision are almost always available. There may be one pair of eyes or more.
Excretory system for the first time appears as separate system . She is presented two or several channels, each of which one end opens outwards, A the other is heavily branched, forming a network of channels of various diameters. The thinnest tubules or capillaries at their ends are closed by special cells - star-shaped(see Fig. 1, D). From these cells, they extend into the lumen of the tubules bunches of eyelashes. Thanks to them permanent job There is no stagnation of fluid in the body of the worm; it enters the tubules and is subsequently excreted. The excretory system in the form of branched canals closed at the ends by stellate cells is called protonephridia.
Reproductive system quite diverse in structure. It can be noted that, in comparison with coelenterates, ciliated worms special excretory ducts appear For
excretion of germ cells. Eyelash worms hermaphrodites. Fertilization - internal.
Reproduction. In most cases sexually. Most worms direct development, but some marine species development occurs with metamorphosis. However, some eyelash worms can reproduce and asexually through transverse division. In this case, in each half of the body there is regeneration missing organs.
Guinea worm
There are worms that live in human blood. These include schistosomes. Their main habitat is blood vessels. However, they are able to penetrate various organs, causing symptoms of damage to the genitourinary system, liver, and kidneys.
The blood may contain larvae of some helminths. For example, in tapeworms this is how they spread throughout the body of the intermediate host. With the blood flow, the larvae migrate to various organs, where they attach and form cysts containing the heads of adult worms. When the latter enter the digestive tract of the final host, they attach to the intestinal wall, giving rise to a sexually mature individual.
Flatworms: general characteristics
The body of flatworms is capable of complex and varied movements.
All flatworms have common features buildings:
- The outer cover is represented by the cuticle. In free-living individuals, it is covered with cilia; the surface of the body of worms is usually smooth.
- Under the outer covering there are several layers of muscle fibers.
- There is no body cavity.
- The digestive system has only one opening - the mouth. The intestine ends blindly. Some worms lack digestive organs altogether. Thus, tapeworms, which absorb nutrients throughout the body from the lumen of the host’s intestine, do not need them.
- There is no circulatory system or blood, as well as respiratory organs.
- The excretory system is represented by a network of tubes that penetrate the entire body.
- The nervous system is primitive. Near the pharynx there are several ganglia from which nerve trunks connected by jumpers extend. Sense organs are formed only in free-living individuals and some worms at the larval stages of development.
The system that is really well developed is the sexual system. Flatworms are hermaphrodites. Reproduction is possible with the participation of 2 individuals or by self-fertilization.
Flukes
The development cycle of trematodes is one of the most complex. Miracidia emerge from eggs released into the external environment. The latter feel comfortable in water and exist for some time as free-living organisms. The next stage is the introduction of miracidia into the first intermediate host. The larva does this using a special cutting apparatus on the head. The host is usually a mollusk.
Their life cycle can occur in several hosts and is accompanied by a regular alternation
Here the miracidium turns into a sporocyst, which gives rise to the next stage of the development cycle - redia. Those, in turn, are the predecessors of cercariae, which leave the intermediate host and again enter the aquatic environment. Next, the development cycle follows one of two options. Cercariae transform into cysts directly during external environment(attached to algae) or in the body of a second intermediate host (mollusk, fish, amphibian).
These are the longest worms with a transparent shell
Infection of the definitive host occurs when it eats infected organs of the intermediate host. The development cycle ends with the attachment of the head from the cyst to the intestinal wall and the development of the adult worm. The latter can reach significant sizes (for example, the wide tapeworm grows up to 10 m long).
For flukes, humans are the final host, but for tapeworms they can also be an intermediate host.
What symptoms occur when a person is infected with a helminth? The clinical picture of the disease is determined, first of all, by which organ is affected. Sexually mature worms usually live in the intestines, so the overall picture of the disease is dominated by symptoms characteristic of digestive disorders: nausea, gas formation, bowel problems, abdominal pain.
Helminths secrete waste products that, when released into the blood, cause poisoning and symptoms of intoxication (fever, fatigue, etc.). In addition, they are perceived by the immune system as an allergen. Therefore, helminthiasis is often accompanied by symptoms allergic reaction(skin rashes, itching).