Table of contents:
Video: Flatworms - General Characteristics And Structure Of Parasite Systems
1 Classification of flatworms
1.1 Characteristics and examples of common representatives of the class
- 2 Parasites
- 3 Features of the structure of flatworm parasites
Relatively simple segmented soft-bodied invertebrates are the flatworm type. The general characteristics of flatworms classify them as bilaterally symmetric individuals without body cavities (spaces between organs). Classes of flatworms number about 25,000 species, of which about 4,000 species live in our latitudes. Species include parasitic flatworms (up to 50%) and free-living flatworms. Let us consider in more detail how many types of helminths there are and their distinctive features.
Classification of flatworms
Flat worms have acquired unique features in the process of evolution. Brief characteristics of the type of flatworms:
- bilateral symmetry;
- differentiated tissues, organs.
The three-layer structure of animals is due to three germ layers, which are laid in the process of embryonic development. Thus, the flatworm parasite has:
- endoderm (inner layer);
- mesoderm (middle layer);
- ectoderm (outer layer).
Type flatworms, classes:
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Characteristics and examples of common representatives of the class
The general characteristics of the type of flatworms do not provide an understanding of each species. Let's take a closer look at the types of flatworms, organ systems, descriptions and examples of representatives:
- Flatworms are class tapeworms. Representatives: pork, bovine tapeworm, wide tapeworm. Parasites need a warm-blooded host. The digestive system of tapeworms is not provided for by the structure, the nervous system, the sense organs are not developed. The body shape of flat tapeworms is flattened with suckers at the anterior (high) end.
- Monogeneans. Types: Gyrodactylus, Dactylogyrus, Neobenedenia, Protopolystoma, Diclidophora. A large number of species parasitize in the bodies of fish. The body shape is long, flat, thickened. The rear end is equipped with a haptor - a suction disc. Each individual has 2 pairs of eyes.
- Ciliary. Representatives: planaria, udonellids. These are not parasitic worms, flat representatives of the class live in water bodies, are predominantly nocturnal, predators. The structure is distinguished by the presence of powerful muscles, cilia for fast movement. These are individuals with well-developed sense organs.
- Trematodes. Representatives: schistosomes, liver flukes, feline fluke. The shape of the body is leaf-shaped, in need of a warm-blooded carrier.
- Cestode-like. Order Amphilinidea. Parasites. The digestive system is absent, the nervous system is poorly developed.
- Aspidogastry. Representatives: Aspidogaster conchicola. Parasites that inhabit molluscs. The peculiarity is the presence of an attachment disc from the rows of suckers located on the abdominal part.
- Gyrocotylides. Representative: gyrocotilide. It parasitizes in fish, has an attachment rosette located in the region of the posterior (lower) end of the body.
For the most part, flatworms are parasites that cause great harm to humans and animals. The most serious helminth is schistosoma. Causing the disease schistosomiasis, which is the second most destructive of all human parasitic diseases, schistosome is second only to malaria.
If the larvae of the pork tapeworm begin to parasitize in the body, then the carrier's nervous system will soon be affected. Helminths cause neurocysticercosis, which provokes epilepsy.
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The type of flatworms, whose general characteristics are extensive, are mostly free-living species. These are scavengers, predators living in water, shaded moist soils, fallen leaves and other environments. The complex developmental cycle of a tapeworm, for example, cestodes or the life cycle of flukes of trematodes, distinguishes both adult forms living in fish, warm-blooded carriers, and intermediate stages. A clutch of trematode eggs is hatched from the main (last) host, while hermaphrodite flatworms (adult cestodes) produce a huge number of segments filled with eggs that spontaneously detach from the parasite and leave the host with feces. Once outside, the segments release eggs, launching a new development of tapeworms, flukes, and other parasites.
Features of the structure of flatworm parasites
|Nervous system||Nerves, ganglia, trunks of the nervous system||The nervous system of flatworms is formed from the ectoderm (outer) layer. the main node is located in the head section of the individual, a branched network of trunks departs from it: through the belly, back, left and right sides. The network is connected with jumpers. In addition, there are separate nerve filaments extending both from the trunks and from the main ganglion to the tissues and organs of the parasite.|
|Digestive||Oral cavity, pharynx, blind-closed intestine||The digestive organs are formed from the endoderm (inner layer). The digestive and excretory organs are closed to the oral cavity. It is located on the upper (front) part of the individual, located on the side of the belly. In individuals, the pharynx acts as a pump; in free-living predatory representatives, the pharynx can turn inside out, move forward, enveloping prey. The intestine is divided into an anterior and a middle part. These internal organs are absent in flat tapeworms.|
|Excretory||Protonephridia||The specific organs characteristic of worms are formed from the mesoderm. Designed for the collection and removal of liquid waste from the parenchyma, they are a type of branching tubules with terminal star-shaped cells.|
|Reproductive||Ovaries and testes are present in one individual||Organs are formed from the mesoderm. Testes are a type of male sex gland that produces fertilization fluid. The ovaries are a type of female gland that produces eggs. Flatworms are called hermaphrodites because of the presence of both types of gonads, but some types of flukes do not have this feature. Fertilization is cross - different individuals must exchange semen, for which they touch their bodies for a few seconds.|
|Musculocutaneous sac||Muscle fibers, epithelium||Organs are formed from the ectoderm. The epithelial layer is a unicellular layered structure on which cilia (in the ciliate class), chitinous hooks-holders (in the class of tape, cestode-like) can be located. Muscle fibers are located under the epithelial layer. They are longitudinal, annular, diagonal and dorsal-abdominal. Due to the wide variety of muscle fibers, worms can quickly perform a number of complex shapes: fold, contract, stretch, ring, and more.|
|Sense organs||Balance organ, light-sensitive eyes, cephalic processes, tactile cells||Helminths of the group of parasitic worms do not have these organs at all or are in an undeveloped state.|
|Respiratory||The respiratory system is absent in individuals. Air intake and removal is carried out by the entire surface of the body. Parasitic helminths are anaerobic creatures, that is, they do not need oxygen.|
|Circulatory||The circulatory system in flatworms is absent.|
There are enough worms in nature, it is only important to know about those that pose a danger to humans. For example, the marine flatworms, turbellaria, are a beautiful primary invertebrate species often found in saltwater. The body cavity of flatworm turbellaria, like many other representatives of the class, does not have internal sections, blood, gas exchange systems, but is equipped with powerful longitudinal and transverse muscles.
Another amazing species is planaria. Predators capable of starving for up to 12 months, significantly decreasing in volume and "eating" themselves. They can retain signs of life even with a reduction in mass and volume by 250-300 times. But as soon as the favorable period begins, individuals develop to normal size.
Flukes, trematodes and other dangerous representatives parasitize on vertebrate warm-blooded representatives of the animal world. Going through complex developmental cycles: from an egg to a mature individual, the worms change hosts. Intermediate: molluscs and fish, final: humans or warm-blooded vertebrates (dogs, cats, cows, sheep, pigs). The size and length of the flatworm of the parasite depends on the species, the largest are tapeworms, reaching 10 meters, the smallest (cestodes) no more than 1-2 cm. But tapeworms, which types, are shown in the table above. The life span of parasites reaches 10-12 years, while a sexually mature individual lays a huge number of eggs every day.