Type Flatworms are a large number of primary invertebrate animals that have a similar structure and characteristics. Type Flatworms - classes: Tape, Flukes, Ciliary. Only the latter live in water bodies, they are perfectly adapted to life in the water, and they can be found in many fresh waters. The class of tapeworms and the class of flukes combines parasitic animals.
Tapeworms are a large class of flatworms with approximately 3,500 different species. The class of tapeworms is also known under other names: cestodes and lentets. The name "cestodes" is a term with a Latin origin (Cestoda). Translated into Russian means "tape" or "belt". It is from this terminology that the name "tapeworms" came from.
The class of tapeworms includes 12 orders, including: cloves, tapeworms, aporids, defilides and others.
Tapeworms: Subclasses
Depending on the features of the structure, tapeworms are divided into 2 subclasses.
Real cestodes . This subclass is quite numerous, represented by different forms. The main characteristics that unite all representatives of these cestodes:
- a body consisting of individual segments;
- many sets of genitals;
- presence of 6 germ hooks in the developing larva.
Subclass Real cestodes, in turn, are divided into several groups. The most common parasites living in the human body and domestic animals are representatives of the orders of chains (Cyclophyllidea) and lentets (Pseudophyllidea).
The class of tapeworms has a second subclass - cetaceous . This subclass includes a small number of units. Distinctive characteristics of cestoids are:
- a body not divided into separate segments;
- only 1 set of genitals;
- The lycophore (a larva developing in an egg) has 10 germ hooks.
The most common species of flatworms belonging to the cestiform subclass is amphilin (Amphilina foliacea). It is a parasite living in the body of sturgeon fish.
Class of tapeworms: general characteristics
According to its characteristics, cestodes are parasites. As a result of their long evolution, they have lost the digestive system, therefore they now live in the digestive organs of other living organisms, including humans. The presence and vital activity of parasites in the human body causes numerous pathological conditions - in this case we are talking about cestodoses (diseases caused by tapeworms).
Over their life, parasitic flatworms (the class of tapeworms) are replaced by several hosts (living organisms, due to which they live and feed). The host chooses the parasite depending on what life cycle it is on.
Life cycle stages
The whole life of tapeworms is divided into 3-4 main stages:
- Adult sexually mature (definitive) parasites live in the body of the final host (usually terrestrial and aquatic vertebrates play this role). It is here that cestodes lay eggs in the intestines.
- At the second stage, the eggs of the lentec from the intestines of the host, together with feces, enter the soil or water. In this environment, a larva is formed from an egg. Eggs developing in water go through a slightly different path of development. First, a larva with cilia appears, capable of swimming freely. Only then does a larva develop from it, ready to pass into the body of an intermediate host.
- The next stage is the development of Finns (bubbly worms). This process occurs after the parasite larvae enter the body of the intermediate host. It can be an invertebrate and vertebrate animal. At the same time, it is not necessary for cestodes to penetrate the intestines; they can live in cavities and body tissues.
- The final stage is the search for the main host. In this case, intestinal entry is mandatory. Here the head of the Finns is inverted, the parasite sticks to the intestinal wall and begins to grow actively and prepare for reproduction.
The structure of tapeworms
In connection with the parasitic lifestyle of tapeworms, the special structure of many systems:
- Reduced digestive system.
- Extremely weak senses and nervous system.
- An important characteristic of the class of tapeworms is the high development of the reproductive system, which ensures the amazing fecundity of individuals. It is thanks to this feature that the tapeworm population does not decrease even with several stages of development and frequent changes of the new host.
The body of tapeworms really resembles a ribbon. The sizes of cestodes are completely dependent on the type of worms. In this class there are the smallest representatives (from 2 mm) and the largest, whose length exceeds 10 m.
Body parts of tapeworms
According to the characteristics of the class tapeworms, their representatives consist of several parts:
Scolex (head), on which there are fixation organs. The structure of the head and methods of attachment there are several, on this basis it is customary to divide tapeworms into several groups. Fixation organs are necessary for attaching the worm to the host tissues. They can be represented by a proboscis, chitinous hooks, suction cups, botria (special suction slots).
Most often in tapeworms there are suckers with hooks, which are located on the head in the shape of a crown. Botria are found in cestodes with a lower level of development, in this case there are no chitin hooks.
Neck (located immediately behind the head and is a growth zone). This part is the bottleneck on the body of the tapeworm. It is here that new segments bud, which gradually grow and shift to the end of the body. Mature segments are located at the posterior end (there are eggs in them). When the joint reaches maturity, it breaks away from the body of the worm and is excreted with the feces of the host.
Strobiles are the joints that make up the entire body of the tapeworm. The number of gates can be different, depending on the species of the worm and its age. Thanks to the constant formation of new strobes and tearing of old ones, the body of worms is renewed throughout his life.
Digestive system
The digestive organs of helminths belonging to the class of tapeworms are absent, since their nutrition occurs at the expense of other organisms. There is a special system for the consumption of nutrients.
The entire surface of the cestode body has a special coating - tegument. It consists of the cytoplasmic outer layer of cells. These cells are distinguished by their elongated shape, which allows the cell nucleus to remain in the submerged layer. The tegument plays an important role, since it participates in the cestode nutrition process - through it, food is absorbed from the intestines of the host.
The tegument has a large number of mitochondria - these special cells are involved in energy metabolism. Thus, tapeworms, being in the intestinal lumen, simply use a ready-made source of host energy for their life without any processing process.
Given the signs of the class of tapeworms and the method of feeding cestodes, there is an opinion that parasites can be removed from the body by prolonged hard starvation. In fact, this method does not always lead to the desired result. The fact is that in the absence of food, tapeworms are able to absorb up to 95% of their own body.
Under the outer layer of the tegument, a membrane is located, and below it the longitudinal and ring muscles, as well as bundles of dorsoventral muscles.
Nervous system
The nervous system has an orthogonal structure. It is represented by a paired ganglion with several pairs of nerve cords extending from it. The most developed are the side trunks. The skin of the worms has receptor and tactile cells, however, there are quite a few of them.
This feature of the structure of the nervous system allows tapeworms to adapt as much as possible to the conditions of life and at the same time actively multiply. So, a small number of receptors makes these parasites practically immune to most drugs with antiparasitic action. A sharp change in living conditions will not affect their activity.
Breeding system
The peculiarity of the reproductive system of cestodes (the class of tapeworms) makes them hermaphroditic, in other words, each worm has female and male reproductive organs in its body (there are some exceptions). In this case, the method of fertilization can also vary. In small worms, there is a cross method, and in large individuals, self-fertilization. This is largely due to the fact that large parasites (5-10 m) live in the host in a single copy, so cross-fertilization in this case is unlikely.
Reproductive organs are present in each individual segment and are not dependent on the set of genital organs of neighboring segments. Most often in the segment there is 1 set of reproductive organs, however, some members of the class have a double set.
Tapeworms are extremely fertile. So, a tapeworm, or as it is also called, bull tapeworm, is capable of producing up to 600 million eggs per year. Given its life expectancy (18-20 years), the number of eggs laid reaches 11 billion.
Excretory system
Helminths belonging to the type of Flatworms and the class of tapeworms have distinctive features. Their excretory system is represented by 4 main longitudinal channels. Many small tubules flow into them, which penetrate the entire body of the helminth. At the ends of small tubules there are pulsating cells whose task is to pump harmful substances accumulated in the tissues.
The main excretory channels are arranged in pairs and pass along the sides of the body next to the trunks of the nervous system. In each pair there is a wide channel (abdominal) and a narrow (dorsal). Wide and narrow channels connect at the head of the worm.
Bull tapeworm
One of the representatives of the tapeworm class is bull tapeworm (unarmed tapeworm). It belongs to the order of Cyclophyllids, the family of Chains. This parasite lives in the body of cattle and humans, causing multiple pathological conditions.
This type of worm is widespread in Latin America, equatorial Africa, certain regions of Eastern Europe and the Philippines.
Bull tapeworm is called an unarmed tapeworm, since its head has only suction cups, it does not have chitin hooks. The word "tapeworm" comes from the word "chain", and it perfectly characterizes the structure of this helminth. He is considered one of the largest representatives of the class of tapeworms. The length of an adult can reach 10 meters.
The unarmed tapeworm belongs to the subclass of Real cestodes, since its body consists of a large number of individual strobils (segments). The length of one segment varies within 2 cm, with regard to their total number, it can reach 1000.
The bovine tapeworm lives up to 18 years old, while for the entire period of development the helminth goes through several stages of development (like all representatives of the Flatworm class of tapeworms).
An adult bovine tapeworm is capable of self-fertilization, as each segment has a set of male and female reproductive apparatus. Ripened eggs are brought out and enter the digestive tract of large animals (for example, cows). Here the larval stage (oncosphere) develops from an egg. With the help of special hooks, she makes a hole in the intestinal wall and thus enters the lymphatic or circulatory system. With a current flow, the oncosphere fluids are transferred to the muscles and connective tissues and pass into the second larval stage (Finn). In this form, they can be for many years.
If a person eats infected meat, the larvae of an unarmed tapeworm enter the intestine and stick to its wall. From this moment, the helminth will begin to grow actively.
Pork tapeworm
Another typical member of the tapeworm class is pork tapeworm. According to many characteristics, the structure of this helminth is similar to the characteristics of a bovine tapeworm, however, there are obvious differences.
If the bovine tapeworm has only suction cups on the scolex, the pork tapeworm uses 4 suckers and chitin hooks for this purpose, which securely fix the parasite to the intestinal wall of its owner. It is for this reason that pork tapeworm is called armed tapeworm.
The length of this worm is much shorter, the head is shorter. Usually it does not exceed 3 m in length.
Despite the fact that the ultimate host of both species is a person, the intermediate hosts may be different. Pig tapeworm most often selects pigs for this purpose (however, it can be any other mammal, even humans). Bovine tapeworm for the intermediate stage of growth chooses cattle and never human.
Ripen segments of pork tapeworm are distinguished in groups, while in the unarmed tapeworm - only one at a time.
The reproductive system of an armed chain is also somewhat different. His ovary consists of 3 lobules (in a bovine tapeworm total of 2), the uterus has 7-12 branches on each side (in a bovine tapeworm - 17-35).
Infection of a person with an adult specimen of pork tapeworm (which lives in the intestines) is called teniosis. If the larvae of this helminth live in the body, we are talking about cysticercosis. Such a disease is extremely rare, but it can be fatal, as these larvae damage the brain.
Wide tape
Wide ribbon - a type of helminth that belongs to the type Flatworms, the class of Tape. Archaeological excavations have shown that this parasite existed on the planet more than 10,000 years ago. Once in the human body, it causes the disease diphyllobothriasis. Like other members of the class, the broad ribbon penetrates the intestines and is fixed there with the help of suction cups. As a result, an ulcer appears at the attachment point on the intestinal wall, and a person experiences severe pain, digestive upsets and a lack of many vitamins.
Absolutely everyone can get diphyllobothriasis. Those who are particularly at risk are those who like raw or unfinished fish (including sushi).
Unlike tapeworms, the tape has an elongated scolex, the dimensions of which are 5 mm long and 1 mm wide.
The body length of the helminth, on the contrary, is very large, and therefore it is called the largest species among tapeworms. Usually it grows up to 10 m, but individuals of 20 m in length are often found.
The segments of the body of the lentec (segments) are wide and flat. Their width is usually 2 times greater than the length. In the body of an adult ribbon can be up to 3 thousand segments.
There are several stages of development of a wide ribbon. During this time, he immediately replaced several owners. Ripened eggs with a segment are separated from the body of the worm and secreted out. Once in the water, the eggs begin to develop, and after a week six-hooked coracidia (embryos) form from them. The first owners of lentets will be small crustaceans that will absorb coracidia. Here, a larva emerges from the embryo. She waits for the crustacean to become food for fish.
In the fish’s stomach, the larva gnaws a hole and moves into the tissue. At this time, a small ribbon (up to 4 cm in length) grows from the larva. In this state, the helminth can stay for a very long time - until the fish becomes food of a person or other animal.
Having examined the brief characteristics of the class of tapeworms, we can come to the conclusion: despite the wide variety of species of these animals, the structure, developmental stages, and other indicators are generally similar.