Characteristics of Phylum Platyhelminthes

The flatworms are members of the phylum Platyhelminthes, which is formed of acoelomate organisms that encompass a variety of free-living and parasitic forms. In the superphylum Lophotrochozoa, which also includes the mollusks and annelids, the majority of the flatworm species are grouped together. The Catenulida and the Rhabditophora are two lineages of Platyhelminthes that are related to one another. The Catenulida, also known as “chain worms,” are a tiny group with only a little more than 100 species. Typically, these worms reproduce asexually by the process of budding. However, the children do not completely separate from their parents, and as a result, they resemble a chain of links. The Rhabditophora, which includes the remaining flatworms listed here, is a genus of flatworms.

Many flatworms are parasitic, including several that are significant human parasites. There are three embryonic tissue layers in flatworms, each of which gives rise to coverings that cover tissues (from ectoderm), internal tissues (from mesoderm), and the lining of the digestive system (from endoderm) (from endoderm). The epidermal tissue is made up of a single layer of cells or a layer of fused cells (syncytium) that covers a layer of circular muscle that is located above a layer of longitudinal muscle in the skin of the body. Mesodermal tissues are made up of mesenchymal cells, which produce collagen and act as a support for secretory cells, which discharge mucus and other components near the surface of the body. The flatworms are acoelomates, which means that their bodies are solid between the surface of their bodies and the cavity of their digestive system; this is known as acoelomate structure.

General features

Importance

Even though certain platyhelminthes (flatworms) are harmless and nondestructive, many other species (especially flukes and tapeworms) are parasitic on humans, domestic animals, or a combination of the two. As a result of systematic meat inspection in Europe, Australia, North and South America, and other parts of the world, human tapeworm infestations have been significantly reduced. However, in areas with inadequate sanitation and where meat is consumed raw, the incidence of tapeworm infestations is considerable. Many people in the Baltic regions are plagued with the broad tapeworm (Diphyllobothrium latum); in portions of the southern United States, a small fraction of the population may be infested with the dwarf tapeworm (Diphyllobothrium spp). (Hymenolepis nana). Because of the widespread use of undercooked steaks and other beef products in Europe and the United States, the beef tapeworm (Taenia saginata) is a prevalent parasite.

Larvae, or parasites in their immature stages, can cause significant harm to their host. The larval stage of the gid parasite of sheep (Multiceps multiceps) usually lodges in the sheep’s brain, causing the sheep to lose consciousness. A variety of Echinococcus cysts, which are fluid-filled sacs containing numerous cells capable of growing into new individuals, can be found practically anywhere in the body of a sheep. Hydatid infections of the liver, brain, or lungs in humans are frequently deadly. It is only where people live in close proximity to dogs that have access to infested sheep for food that the infestation takes hold.

Fluke species that are parasitic on humans have been identified in at least 36 different species. Although endemic (local) centres of infection can be found in practically all nations, the Far East, Africa, and tropical America are the most common places to find extensive infestations. Many species, including the lung fluke Paragonimus westermani found in crayfish and crabs, the intestinal flukes Heterophyes heterophyes and Metagonimus yokogawai and the liver fluke Opisthorchis sinensis found in fish, and the intestinal fluke Fasciolopsis buski found in plants, are ingested as cysts, known as metacercariae, in uncooked food. Blood fluke larvae (also known as cercariae) are free-swimming parasites that enter the human body through the skin. These parasites, as well as the others listed below, inflict a great deal of suffering and death in humans. Although attempts have been made to control certain flukes by the removal of their mollusc hosts have been unsuccessful, there is still hope. The sheep liver fluke (Fasciola hepatica) is a parasite that can cause severe and fatal epidemics (liver rot) in domestic animals, particularly sheep. These animals become infected after ingesting metacercariae that have encrusted themselves on grass. Monogenea are a common pest of fish in hatcheries and home aquariums, and they can be difficult to control.

Size range

Turbellarians are typically smaller than five millimetres (0.2 inch) in length, with many of them being minuscule in size. The planarians are the largest members of this class, with some reaching a length of up to 0.5 metre (approximately 20 inches). Generally speaking, trematodes are between one and ten millimetres (0.04 to 0.4 inch) in length; nevertheless, members of some species can grow to reach several centimetres in length. Even though the smallest cestodes are less than one millimetre (0.04 inch) in length, individuals of a few species can grow to reach more than 15 metres (50 feet) in length. The Monogenea have a length ranging from 0.5 millimetres to 30 millimetres (0.02 to 1.2 inches). Aspidogastrea can range in length from a few millimetres to more than 100 mm.

Regeneration

It is found in two classes of Platyhelminthes: Turbellaria and Cestoda, both of which have the ability to regenerate tissue in addition to just mending wounds.

Turbellaria

Turbellarians, and in particular planaria, have been extensively studied in the field of regeneration research. The most powerful regeneration abilities are seen in organisms that are capable of asexual reproduction. Pieces of the turbellarian Stenostomum, for example, can be used to create wholly new worms from practically any portion of the animal. Sometimes the regeneration of very minute fragments might result in the development of defective creatures (for example, those lacking a head).

Other Turbellaria have limited head regeneration, with fragments from the front region or tissues comprising the cerebral ganglia being the only areas that regenerate (brain). While wounds made anterior to this ganglion are incapable of regeneration, cuts made posterior to it can result in the regeneration of the entire posterior area, including the throat and the reproductive system in a number of different species. The polarity of the cut portions is maintained, i.e., the anterior zone of the cut piece regenerates the head, and the posterior zone regenerates the tail. Transfer of an area in front of the pharynx into the posterior region of another individual has the effect of inducing that region to create a pharyngeal zone, which finally results in the formation of a pharynx in that individual. This new pharyngeal zone has now been determined, and if it is removed, it will regenerate into a new pharynx, according to the researchers.

Cestoda

Cestodes are capable of regeneration, which is uncommon in parasitic worms in general but common in cestodes. The head (scolex) and neck portion of most tapeworms are capable of regeneration. The presence of this feature makes it difficult to cure people with tapeworm infections; treatment may merely destroy the tapeworm’s body, or strobila, leaving the scolex attached to the intestinal wall of the host and thus capable of creating a new strobila, thereby reinitiating the infestation. Cestode larvae from a variety of taxa have the ability to recover from cut places. One type of Sparganum prolifer, a human parasite, is a branching larval form that is capable of both asexual proliferation and regeneration.

Conclusion

Organisms belonging to the phylum Platyhelminthes have a ribbon-shaped body with a delicate texture, and its dorso-ventrally flattened from top to bottom shape distinguishes them. They are the most basic bilaterally symmetrical organisms on the planet, and they have a digestive cavity, which means that they have organs.

Even though certain platyhelminthes (flatworms) are harmless and nondestructive, many other species (especially flukes and tapeworms) are parasitic on humans, domestic animals, or a combination of the two. They live as parasites in the human body, primarily in the intestinal and digestive tracts of the infected person. They improve the likelihood of organic farming succeeding. They helped to promote the popularity of raw prepared meals, such as meat, seafood, and vegetables imported from other countries.