The type of animal, flatworms, which is part of a 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, including annelids and roundworms, arthropods, mollusks, etc. belong to it.
Appearance and description of flatworms
Platyhelminthes from the ancient Greek language translates as "wide helminth." These are primitive invertebrate 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 land with high humidity. They are characterized by a complex life cycle, during which the intermediate hosts change until the worms settle in the organs of the final host.
Species of flatworms are diverse and widespread throughout the world. There are about 25 thousand of them.
Scientific classification of flatworms
Flatworms belong to the kingdom of Bilateral (symmetrical on both sides) primary animals. In connection with some disputes that arose when trying to divide flatworms into different groups, scientists attribute them to the paraphyletic group. It includes representatives of a small part of the descendants of the same ancestors.
The structure of the internal organs of a flat worm
The body of flatworms is elongated and flattened, without a cavity inside. That is, his entire space is filled with cells. Layers of musculature are located inside, which together with the shell of the worm form a musculocutaneous sac.
There are systems of internal organs:
- The digestive system is represented by the mouth and the cecum (with no outlet). Nutrients enter through the mouth and 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 allocation occurs throughout the surface of the body.
- The reproductive system is represented by both female (ovaries) and male (testes) genital organs. Hermaphrodite flatworms.
Differences between flat and round worms
Roundworms differ from flatworms in that their cross-section has a round shape. Roundworms are also commonly called nematodes. Having a bilaterally symmetrical body structure, they have developed musculature. But the main difference from flatworms is that round ones have an internal body cavity, and flat ones do not.
Variety of Flatworm Classes
Table "Flatworms" clearly shows the division of the species into classes, which modern science has seven.
Class name | Habitat | Dimensions | Life cycle |
Monogenies (flukes) | Using the attachment disk at the posterior end of the worm, Monogenae attaches to the gills of fish and the skin of amphibians and turtles | Very small, on average no more than 1 mm | For all its life, the worm has one host, which gets into the form of a freely floating larva |
Cestode-shaped | Parasitize in the body cavity of freshwater fish and turtles | Length ranges from 2.5 to 38 cm | Larvae develop in the body of crustaceans when an egg is swallowed. After eating a crustacean with an aquatic vertebrate, an already adult individual easily moves from the intestines of the new host into the body cavity, where it lives and multiplies |
Aspidogaster | They live in the bodies of mollusks, freshwater and marine fish | An adult rarely reaches a size of more than 15 mm | Several times host changes occur over the life cycle of worms |
Trematodes (flukes) | They are parasites of vertebrate and invertebrate animals, humans. They live in the intestines, gall bladder, liver | Dimensions vary depending on the parasitic site of the adult worm and can be from 2 mm to 1 m | Over the whole life they have several owners. The larva first lives in a gastropod, which subsequently dies. Gets inside when swallowing cercaria (ready to colonize the larvae of the final host) |
Gyrocotilides | Are parasites of cartilaginous chimera fish in the spiral fold of the intestine | 2 to 20 cm | 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 is not confirmed experimentally |
Tape | The habitat of flatworms is the intestines of a mammal and a person, to the wall of which they are firmly attached with the head | They can reach sizes up to 10 m. | Reproduction occurs in the host's body, the eggs go into the water, and then to land. A larva appears, which after three stages of development turns into a worm, ready to parasitize and develop. Adults can change owners |
Ciliary | Mostly free-living worms live in fresh and salty water bodies, sometimes in moist soil | Body length ranges from microscopic sizes to 40 cm | An adult worm larva emerges from an egg, inhabiting plankton, until it grows |
Flatworm classes 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 mollusks. They completely swallow small prey or, with strong sucking movements, tear off pieces from it.
The body of the worms is able to regenerate itself. A striking representative is the planaria, in which even a small part of the body re-grows into a full-fledged individual.
Flatworms in Home Aquariums
Helminths can be a big problem for lovers of fish farming in aquariums.
The habitat of flatworms is mainly aquatic. As flukes, flatworms can be attached by means of an attachment disk to the surface of the gills and skin of aquarium fish.
Adult worms lay eggs, from which larvae that live on the skin of fish come out. Gradually, they crawl to the gills, where they grow, reaching puberty.
Young fish are more susceptible to parasites, weaker. 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 species of flatworms enter a home aquarium with soil, live food. Their larvae can be found on the surface of algae, on the skin of new fish populated in the aquarium.
To rid parasites of domestic fish, they must be kept in baths with the addition of bicillin-5 and salt for 5 minutes.
Dangerous for human health parasites
The topic of flatworms, in particular, the problem of combating parasites, is relevant not only for fish, shellfish 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 tape). Infection with them can occur if a raw, poorly salted fish is present in the diet. In the small intestine of a person, the ribbon can live for decades, reaching a length of up to 20 m.
- Aeniarhynchus saginatus ( bovine tapeworm). The habitat of flatworms is the intestines of humans and cattle. Sucking to its walls, the helminth grows up to 10 m. Larvae can be located in other internal organs, in hard-to-reach places (brain, muscles, liver), so often it is impossible to completely get rid of them. The patient may die. Infection occurs when helminth eggs enter the stomach with insufficiently thermally processed food, from dirty hands.
- Echinococcus (Echinococcus) is often found in dogs and cats, from them passing into the body to humans. Despite its small size - only 5 mm - the ability of its larvae to form Finns paralyzing internal organs is deadly. 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 catch the larvae secreted by the dog with feces, which spread to the wool, and from there to all household items and food.
- Hepatic trematode is the culprit of cholecystitis, hepatic colic, disturbances in the functioning of the stomach and intestines, and allergies. The habitat of flatworms is mainly the human liver and warm-blooded animals, bile ducts. 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.
Helminth infection prevention
Preventive measures for the ingestion of eggs and larvae of helminths in the human body are as follows:
- It is necessary to wash your hands thoroughly with soap before each meal, after visiting public places, toilets, streets, talking with pets.
- Wash raw vegetables and fruits with warm water and soap.
- Do not eat raw meat and fish.
- For a long time to heat food, especially meat, fish.
- Pay attention to the timely prevention of helminthic infestations of domestic animals.
- Regularly, at least once a year, take an analysis of feces for worm eggs.