Type Flatworms are a large number of primary invertebrates that have similar structure and characteristics. Type Flatworms - classes: Tapeworms, 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 Tapeworms and the class Flukes combine parasitic animals.
Tapeworms are a large class of flatworms with approximately 3,500 different species. The class Tapeworms is also known by other names: cestodes and tapeworms. The name "cestodes" is a term with Latin origin (Cestoda). Translated into Russian means "tape" or "belt". It is from this terminology that the name "tape" worms came about.
The class Tapeworms includes 12 orders, including: carnations, tapeworms, aporids, defilides and others.
Tapeworms: subclasses
Depending on the structural features, Tapeworms are divided into 2 subclasses.
Real cestodes. This subclass is quite numerous, represented by different forms. Main characteristics,uniting all representatives of true cestodes:
- body consisting of individual segments;
- multiple genital kits;
- presence of 6 embryonic hooks in the developing larva.
Subclass True cestodes, in turn, is divided into several orders. The most common parasites living in the human body and domestic animals are representatives of the orders of tapeworms (Cyclophyllidea) and tapeworms (Pseudophyllidea).
The class Tapeworms has a second subclass - cestiformes. This subclass includes a small number of units. The distinguishing characteristics of cests are:
- body not divided into separate segments;
- only 1 set of sex organs;
- lycophora (the larva that develops in the egg) has 10 embryonic hooks.
The most common type of flatworm, belonging to the subclass of cests, is amphilina (Amphilina foliacea). This is a parasite that lives in the body of sturgeons.
Class Tapeworms: general characteristics
According to their characteristics, cestodes are parasites. As a result of their long evolution, they lost the organs of the digestive system, so now they live in the digestive organs of other living organisms, including humans. The presence and activity of parasites in the human body causes numerous pathological conditions - in this case we are talking about cestodiasis (diseases caused by tapeworms).
For my lifeparasitic flatworms (class Tapeworms) change several hosts (living organisms, due to which they live and feed). The parasite chooses a host depending on what life cycle it is on.
Life cycle steps
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 act in this role). This is where the cestodes lay their eggs in the gut.
- At the second stage, the eggs of tapeworms from the intestines of the host, along with feces, enter the soil or water. In this environment, a larva develops from an egg. Eggs that develop in water follow a slightly different path of development. First, a larva with cilia appears from them, able to swim freely. Only then a larva develops from it, ready to move into the body of an intermediate host.
- The next stage is the development of Finns (bubbly worms). This process occurs after the entry of the parasite larva into the body of the intermediate host. They can be invertebrate and vertebrate animal. At the same time, cestodes do not have to penetrate the intestines, they can live in the cavities and tissues of the body.
- The final stage is the search for the main owner. In this case, ingestion is mandatory. Here the head of the Finn turns inside out, the parasite sticks to the intestinal wall and begins to actively grow and prepare for reproduction.
Structure of tapeworms
Due to the parasitic lifestyle of tapeworms, the special structure of many systems:
- Reduced digestive system.
- Extremely weak sense organs and nervous system.
- An important characteristic of the class of tapeworms is the high development of the reproductive system, which ensures the amazing fertility of individuals. It is thanks to this feature that the population of tapeworms does not decrease, even taking into account several stages of development and the frequent change of a new host.
The body of tapeworms really resembles a tape. The sizes of cestodes completely depend on the type of worms. This class has the smallest representatives (from 2 mm) and the largest, whose length exceeds 10 m.
Departments of the body of tapeworms
According to the characteristics of the class Tapeworms, their representatives consist of several parts:
Scolex (head), on which there are organs of fixation. There are several head structures and attachment methods; on this basis, it is customary to divide tapeworms into several groups. Fixation organs are necessary for attaching the worm to host tissues. They can be represented by a proboscis, chitinous hooks, suckers, bothria (special suction slots).
Most often, tapeworms have suckers with hooks that are located on the crown-shaped head. Bothria are found in cestodes with a lower level of development, in which case chitin hooks are absent.
Neck (located immediately behind the head and is a growth zone). This part is the narrowest point on the tapeworm's body. Right herenew segments bud off, which gradually grow and move towards the end of the body. Mature segments are located at the posterior end (they contain eggs). When the segment reaches maturity, it detaches from the worm's body and is excreted in the host's feces.
Strobili are the segments that make up the entire body of the tapeworm. The number of strobili can be different, depending on the species of the worm and its age. Due to the constant formation of new strobili and tearing off the old ones, the body of the worms is updated throughout its life.
Digestive system
Digestive organs in helminths belonging to the class of tapeworms are absent, since they feed on other organisms. There is a special system for consuming nutrients.
The entire surface of the body of the cestode has a special coating - tegument. It consists of a cytoplasmic outer layer of cells. These cells are distinguished by an elongated shape, which allows the cell nucleus to remain in the submerged layer. The tegument plays an important role, since it is involved in the process of nutrition of the cestode - food is absorbed from the host intestine through it.
Tegument has a large number of mitochondria - these special cells are involved in energy exchange. Thus, tapeworms, being in the intestinal lumen, simply use the already prepared host energy source for their life activity without any processing.
Given the characteristics of the class Tapeworms and the way cestodes feed, there is an opinion that it is possible to remove parasites from the bodyby prolonged 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 there is a membrane, and under it are the longitudinal and annular 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 lateral trunks. The skin of 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 to the conditions of life as much as possible 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.
Reproduction system
The peculiarity of the reproductive system of cestodes (class 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 may also differ. 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 organism in one copy, so cross-fertilization in this case is unlikely.
Reproductive organsare present in each individual segment and do not depend on the set of genital organs of neighboring segments. Most often, a segment contains 1 set of reproductive organs, however, some members of the class have a double set.
Tapeworms are extremely fertile. So, tapeworm, or as it is also called, bovine tapeworm, is capable of producing up to 600 million eggs a year. Given its longevity (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 canals. Many small tubules flow into them, which permeate the entire body of the helminth. At the ends of small tubules there are pulsating cells, the task of which is to inject harmful substances accumulated in the tissues.
The main excretory canals are located in pairs and run 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 one (dorsal). The wide and narrow canals join at the head of the worm.
Bull tapeworm
One of the representatives of the class Tapeworms is the bovine tapeworm (naked tapeworm). It belongs to the order of Cyclophyllids, 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, and certain regionsEastern Europe and the Philippines.
The bovine tapeworm is called an unarmed tapeworm, since its head has only suckers, it has no chitinous hooks. The word "tape" comes from the word "chain", and it perfectly describes the structure of this helminth. It is considered one of the largest representatives of the class Tapeworms. The length of an adult can reach 10 meters.
The unarmed tapeworm belongs to the subclass True cestodes, since its body consists of a large number of individual strobili (segments). The length of one segment varies within 2 cm, as for their total number, it can reach 1000.
The bovine tapeworm lives up to 18 years, while for the entire period of development the helminth goes through several stages of development (like all representatives of the Flatworm type of the Tapeworm class).
Adult bovine tapeworm is capable of self-fertilization, since each segment has a set of male and female reproductive organs. Ripe eggs are brought out and enter the digestive tract of large animals (for example, cows). Here, the larval stage (oncosphere) develops from the egg. With the help of special hooks, it makes a hole in the intestinal wall and thus enters the lymphatic or circulatory system. With the current of the fluid, the oncospheres 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 contaminated meat,larvae of an unarmed tapeworm enter the intestine and stick to its wall. From this moment on, the helminth will begin to grow actively.
Pork tapeworm
Another typical representative of the class of tapeworms is pork tapeworm. According to many characteristics, the structure of this helminth is similar to the characteristics of the bull tapeworm, but there are also obvious differences.
If the bovine tapeworm has only suckers for attachment on the scolex, then the pork tapeworm uses 4 suckers and chitinous hooks for this, which securely fix the parasite to the intestinal wall of its host. It is for this reason that the pork tapeworm is called the armed tapeworm.
The length of this worm is much shorter, the head is smaller. It usually does not exceed 3 m in length.
Despite the fact that the final owner of both species is a man, the intermediate owners can be different. The tapeworm most often chooses pigs for this purpose (however, any other mammal, even humans, can become them). The tapeworm for the intermediate growth stage chooses cattle and never humans.
Mature segments of the tapeworm stand out in groups, while in an unarmed tapeworm - only one at a time.
The reproductive system of the armed tapeworm is also somewhat different. His ovary consists of 3 lobules (in the bull tapeworm only 2), the uterus has 7-12 branches on each side (in the bull tapeworm - 17-35).
Infection of a person with an adult tapeworm (which lives in the intestines) is called taeniasis. If in the bodylive larvae of this helminth, we are talking about cysticercosis. This disease is extremely rare, but it can be fatal, as these larvae damage the brain.
Wide Tape
Wide tapeworm - a type of helminth that belongs to the type Flatworms, the class Tapeworms. 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 representatives of the class, the wide tapeworm penetrates the intestines and is fixed there with the help of suction cups. As a result, an ulcer appears at the attachment site on the intestinal wall, and the person experiences severe pain, indigestion and a lack of many vitamins.
Absolutely everyone can become infected with diphyllobothriasis. Those who love raw or undercooked fish (including sushi) are at particular risk.
Unlike tapeworms, the tapeworm has an elongated scolex, the dimensions of which are 5 mm long and 1 mm wide.
The length of the body of the helminth, on the contrary, is very large, in connection with which it is called the largest species among tapeworms. Usually it grows up to 10 m, however, individuals of 20 m in length are also often found.
The segments of the body of the tapeworm (segments) are wide and flat. Their width is usually 2 times greater than the length. In the body of an adult tapeworm, there can be up to 3 thousand segments.
There are several stages of development of a wide ribbon. During this time heseveral owners change at once. Ripe eggs, together with the segment, are separated from the body of the worm and stand out. Once in the water, the eggs begin to develop, and after a week, six-hooked coracidia (embryos) are formed from them. The first owners of the tapeworms will be small crustaceans that will absorb the coracidia. Here the larva emerges from the embryo. She is waiting for the crustacean to become fish food.
In the stomach of the fish, the larva gnaws a hole and moves into the tissue. At this time, a small ribbon grows from the larva (up to 4 cm in length). In this state, the helminth can stay for a very long time - until the fish becomes food for a person or another animal.
After reviewing the brief characteristics of the class Tapeworms, we can conclude: despite the wide variety of species of these animals, the structure, developmental stages and other indicators are generally similar.
