The type of animal flatworms, which are included in the group of bilaterally symmetrical, is studied by the science of biology. Flatworms (Platyhelminthes) are not the only representatives of this group, more than 90% of animals belong to it, including annelids and roundworms, arthropods, molluscs, etc.
Appearance and description of flatworms
Platyhelminthes is translated from ancient Greek as "broad helminth". These are invertebrate primitive worms that lack a body cavity designed to collect, distribute and excrete nutrients. Most of them are parasites, and some live in water bodies or on the ground with high humidity. They are characterized by a complex life cycle, during which there is a change of intermediate hosts, until the worms settle in the organs of the final host.
Types of flatworms are diverse and distributed throughout the world. There are about 25 thousand of them.
Scientific classification of flatworms
Flatworms belong to the Bilateral kingdom(symmetrical on both sides) protostomes. In connection with some disputes that arose when trying to separate flatworms into different groups, scientists attribute them to a paraphyletic group. It includes representatives of a small part of the descendants of the same ancestors.
The structure of the internal organs of a flatworm
The body of flatworms is elongated and flattened, without a cavity inside. That is, its entire space is filled with cells. Inside are layers of muscles, which, together with the shell of the worm, form a musculocutaneous sac.
Internal organ systems present:
- The digestive system is represented by the mouth and the blind (having no exit) intestine. Nutrients are taken in through the mouth or can be absorbed through the entire surface of the body.
- The nervous system consists of brain ganglia and nerve columns. Some classes of flatworms have primitive organs of balance, vision.
- The excretory system consists of special tubules, but most often the excretion occurs over the entire surface of the body.
- The reproductive system is represented by both female (ovaries) and male (testes) reproductive organs. Flatworms are hermaphrodites.
Differences between flatworms and roundworms
Roundworms differ from flatworms in that their body is round in cross section. Roundworms are also called nematodes. Possessing a bilaterally symmetrical body structure, they have a developedmuscles. But the main difference from flatworms is that roundworms have an internal body cavity, while flatworms do not.
Diversity of classes of flatworms
The table "Flatworms" clearly shows the division of the species into classes, of which modern science has seven.
| Class name | Habitat | Sizes | Life cycle |
| Monogenenes (flukes) | Using an attachment disc at the posterior end of the worm, Monogenea is attached to the gills of fish and the skin of amphibians and turtles | Very small, no more than 1 mm on average | For the whole life the worm has one host, to which it gets in the form of a free-swimming larva |
| Cestoids | Parasitic in the body cavity of freshwater fish and turtles | Length ranges from 2.5cm to 38cm |
The larvae develop in the body of crustaceans when the egg is swallowed. After eating a crustacean by aquatic vertebrates, an already adult individual easily moves from the intestines of a new host to the body cavity, where it lives and reproduces |
| Aspidogaster | Inhabit the bodies of shellfish, freshwater and marine fish | Adult seldom grows larger than 15mm | Several host changes occur during the life cycle of worms |
| Trematodes (flukes) | They are parasites of vertebrates and invertebrates, humans. They live in the intestines, gallbladder, liver | Dimensions vary depending on the place of parasitization of an adult worm and can be from 2 mm to 1m | They have several owners throughout their lives. The larva first lives in a gastropod, which subsequently dies. Ingested by ingestion of cercariae (ready to colonize the organs of the definitive larval host) |
| Gyrocotylides | They are parasites of cartilaginous chimera fish in the spiral fold of the intestine | 2 to 20cm |
Hypothetically, the larvae first develop in the body of the intermediate host, and only then move into the fish. But due to the fact that chimeric fish are deep-sea, the hypothesis has not been experimentally confirmed |
| Tape | The habitat of flatworms is the intestines of a mammal and a person, to the wall of which they firmly stick with the help of the head | Can reach sizes up to 10 m. | Reproduction occurs in the body of the host, the eggs go into the water, and then onto land. A larva appears, which after three stages of development turns into a worm, ready to parasitize and develop. Adults can change hosts |
| Ciliary | Mostly free-living worms, found in fresh and s alt water, sometimes in moist soil | Body length ranges frommicroscopic sizes up to 40 cm | The adult worm-like larva emerges from the egg, living among plankton until it grows up |
Classes of flatworms, all but one (ciliary worms), are parasites. Many of them significantly affect the populations of freshwater and marine fish, reducing them.
Having the ability to parasitize on the skin, under the gills, worms become sources of various infections getting inside, which causes massive infection and death of fish.
Ciliary worms
Ciliary worms (turbellaria) are predators that eat small invertebrates, arthropods and even large molluscs. They swallow small prey whole or tear off pieces from it with strong sucking movements.
The body of worms is able to regenerate itself. A bright representative is the planarian, in which even a small part of the body grows again into a full-fledged individual.
Flatworms in home aquariums
Helminths can be a big problem for aquarium fish lovers.
The habitat of flatworms is mostly aquatic. As flukes, flatworms can attach by means of an attachment disc to the surface of the gills and skin of aquarium fish.
Adult worms lay eggs that hatch into larvae that live on the skin of the fish. Gradually, they crawl onto the gills, where they grow, reaching sexual maturity.
Young fishmore susceptible to parasites, weaker ones. The formation of a large accumulation of helminths on the gills leads to the death of the organ, and subsequently to the death of the fish.
Some types of flatworms get into the home aquarium with soil, live food. Their larvae can be on the surface of algae, on the skin of new fish settled in the aquarium.
To rid domestic fish of parasites, it is necessary to keep them in baths with the addition of bicillin-5 and s alt for 5 minutes.
Dangerous to human he alth parasites
The topic of flatworms, in particular, the problem of parasite control, is relevant not only for fish, mollusks and crustaceans. There is a risk of human infection with helminths, the fight against which can be long and painful.
Some types of parasites in humans and other mammals:
- Pseudophyllidea (wide tapeworm). Infection with them can occur if raw, poorly s alted fish is present in the diet. In the human small intestine, the tapeworm can live for decades, reaching a length of up to 20 m.
- Aeniarhynchus saginatus (ox tapeworm). The habitat of flatworms is the intestines of humans and cattle. Sticking to its walls, the helminth grows up to 10 m. The larvae can be in other internal organs, in hard-to-reach places (brain, muscles, liver), so it is often impossible to completely get rid of them. The patient may be fatal. Infection occurs when helminth eggs enter the stomach with insufficiently thermally processedfood, from dirty hands.
- Echinococcus (Echinococcus) is often found in dogs and cats, from them passing into the body to humans. Despite their small size - only 5 mm - the ability of its larvae to form Finns that paralyze internal organs is deadly. The larvae are able to penetrate into the respiratory, bone, urinary systems. Echinococcus flatworms are often found in the brain, liver and other internal organs. A person can easily become infected with larvae excreted in the feces of a dog, which spread to the coat, and from there to all household items and food.
- The liver fluke is the culprit of cholecystitis, hepatic colic, disorders of the stomach and intestines, allergies. The habitat of flatworms is mainly the liver of humans and warm-blooded animals, the biliary tract. The body length of the fluke does not exceed 3 cm. The peculiarity is that not only mature individuals, but also their larvae are capable of reproduction.
Prevention of helminth infection
Preventive measures for getting eggs and larvae of helminths into the human body are as follows:
- You must wash your hands thoroughly with soap and water before every meal, after visiting public places, toilets, outdoors, interacting with pets.
- Wash raw vegetables and fruits with warm soapy water.
- Do not eat raw meat and fish.
- Cook food for a long time, especially meat, fish.
- Pay attention to the timely prevention of helminthic invasionspets.
- Regularly, at least once a year, take a stool test for worm eggs.
