Flatworm

Flatworms, as the name suggests, are present in a flat shape. Flatworm body is flat and they are also known as Platyhelminthes. It is a Phyllostachys with two faces, a relatively unsegmented simple soft invertebrate. Unlike other bilateral animals, they are animals without cavities, without special organs of circulation and respiration, which limits their flat shape, allowing oxygen and nutrients to diffuse through their bodies. The digestive cavity has a single opening for ingestion that is the absorption of nutrients and digestion that is the removal of undigested waste, so food cannot be processed continuously. Flatworms are divided into Turbellaria, which are mostly non-parasitic animals such as planarians, and three completely parasitic groups are Trematoda, Monogenea, and Cestoda. This gave us a brief idea of Platyhelminthes meaning. 

About Flatworms

Free-living flatworms are mostly predators, living in water or a cool, moist terrestrial environment, such as fallen leaves. Tapeworms and flukes have a complex life cycle. They live as parasites in the digestive system of fish or terrestrial vertebrates at the mature stage and infect secondary hosts in the intermediate stage. Fluke eggs are shed from their main host, and adult tapeworms produce a large number of hermaphrodite segments, which fall off when they mature and then release the eggs. Unlike other parasitic groups, the monogenic group is an external parasite that infects aquatic animals, and their larvae mutate into adults after attaching to a suitable host. 

Because they have no internal body cavity, flatworms are considered to be the primitive stage of bilateral animal evolution, that is, animals with bilateral symmetry, and therefore different front and back end. However, analysis conducted since the mid-1980s has separated a subgroup of Acoelomorpha as basal bilateral animals, closer to primitive bilateral animals than any other modern group. The remaining flat animals form a monophyletic group that contains all and only the descendants of a common ancestor, and the common ancestor itself is a member of the group. Platyhelminthes redefined is part of Lophotrochozoa, which is one of the three main groups of more complex bilateral animals. 

These analyzes concluded that the redefined flat animals (excluding Acoelomorpha) consist of two monophyletic subgroups, Catenulida and Rhabditophora, while Cestoda, Trematoda, and Monogenea form a monophyletic subgroup within a Rhabditophora branch. Therefore, the traditional subgroup of flat animals Planarian flatworm is now considered collateral because it excludes the completely parasitic groups, even if they are descendants of a group of Planaria. 

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Features of Flatworms

Flatworms or planarian flatworms are bilaterally symmetrical animals. The left and right sides are mirror images of each other, this also means that they have different upper and lower surfaces and different head and tail end. Like other bilateral animals, they have three main cell layers that are the endoderm, mesoderm, and ectoderm. The radially symmetrical cnidaria and comb jellyfish. Unlike other bilateral animals, flatworms have no internal body cavity, which is why they are described as acystic worms. They also lack specialized respiratory and circulatory organs, both of which are defining features when classifying the anatomical structure of flatworms. Their bodies are soft and not divided.  

Classification of Flatworms 

The types of flatworms are divided into four groups: Turbellaria, Trematoda, Monogenea, and Cestoda. This classification has long been considered artificial. 

Turbellaria

These have about 4,500 species. Most of them are living, ranging from 1 to 600 millimetres long. Most are predators or scavengers. Most terrestrial species are active at night and live in cool, damp places such as fallen leaves or decaying wood. However, some are symbionts of other animals, such as crustaceans, and others are parasites. Free-living flatworms are mostly black, brown, or gray, but some larger flatworms are brightly coloured. Acoela and Nemertodermatida are traditionally considered turbellarians. Some planarians have a simple, cilia-lined pharynx, usually using cilia to sweep food particles and small prey into their mouths, usually in the middle of their bottom. 

Most other peatlands have an inverted pharynx and the mouth of different species can be anywhere on the bottom. Freshwater species like the Microstomum caudatum can open a mouth almost as wide as its body length and swallow prey as large as it is. Most peatlands have pigment cup ocelli that mean they have small eyes.  Most species have one pair, but other species have two or even three pairs of eyes. Some large species have groups of eyes on the brain, mounted on the tentacles, or evenly distributed around the edges of the body. Ocelli can only tell which direction the light is coming from, so animals can avoid it. 

Some groups have a fluid-filled venous cavity that contains one small solid particle, or in some groups, there are two. These statocysts are believed to act as balance and acceleration sensors because they play the same role in cnidarians and comb jelly. However, cloudy statocysts do not detect cilia, so how they perceive the movement and position of solid particles is unknown. On the other hand, most ciliated touch sensor cells are scattered throughout their bodies, especially in and around the tentacles. Planarian flatworms are a subgroup of the animal series, known for their ability to regenerate after their bodies are cut off. The experiments show that the new head grows faster in those fragments that were originally located closer to the original head. This indicates that head growth is controlled by a chemical whose concentration gradually decreases throughout the body from start to finish. 

Many turbellarians clone themselves by dividing horizontally or vertically, while others reproduce by budding. The vast majority of planarians are hermaphrodites and they fertilize their eggs through mating in the body. Some of the larger aquatic species mate via penile enclosures, a duel in which everyone tries to conceive someone else, with the loser playing the role of a female to develop eggs. In most species, micro adults appear when the eggs hatch, but some large species produce plankton-like larvae. This gave us a clear idea about Platyhelminthes meaning. 

Trematoda 

These are often called trematodes because most have a flat diamond shape, similar to flounder. They are also known as hammerhead flatworms. There are about 11,000 species, more than all other flat animals combined, second only to roundworms in metazoan parasites. Adults usually have two attachments that are a ring around the mouth and a larger suction cup, along the lower half of the free-living flatworm. Although the name Digeneans means two generations, most of them have a very complex life cycle, up to seven stages, depending on the combination of environments found in the early stages, the most important factor if the eggs are deposited on land or in water. 

The intermediate stage transfers the parasite from one host to another. The last host for adult development is terrestrial vertebrates; the earliest host in the larval stage is usually a snail, which can live on land or in water, and in many cases, fish or arthropods are the second hosts. The intestinal fluke is born in the intestine of a snail and then moves towards the fish, where it penetrates the body and forms a sac in the meat, and then migrates to the small intestine on land to eat it raw. Fish animals, the eggs are finally produced. discharged and ingested by snails, thus completing this cycle. Opisthorchis viverrini has a similar life cycle, is found in Southeast Asia, and can infect the human liver, causing cholangiocarcinoma. 

Schistosomiasis, which causes the devastating tropical disease schistosomiasis, also falls into this category. The length of adults is between 0.2 and 6 millimetres. The individual adult parents are single-sexed, and in some species, the elongated females live in closed grooves that run the length of the male's body, with some of them laying eggs. In all species, adults have complex reproductive systems that can produce 10,000 to 100,000 times more eggs than free-living flatworms. 

In addition, the intermediate stage of life in snails reproduces asexually. Adults of different species infect different parts of the final host, such as the intestines, lungs, large blood vessels, and liver. Adults use a relatively large muscular pharynx to ingest cells, cellular debris, mucus, body fluids, or blood. During the adult and snail dwelling stage, the external syncytium absorbs dissolved nutrients from the host. Adults can survive for a long time without oxygen. 

Cestoda 

They are often called tapeworms because of their flat, thin, and very long bodies. Adults of 3,400 species of tapeworms are endoparasites and are known as parasitic flatworms. Cestodes have no mouth or internal organs. The syncytial skin absorbs nutrients from the host, mainly carbohydrates and amino acids, and chemically disguises them to prevent the host's immune system from attacking. A shortage of carbohydrates in the host's diet can slow down the growth of parasites and can even kill them. Their metabolism usually uses simple but inefficient chemical processes to compensate for this inefficiency by consuming a large amount of food relative to their physical size. 

In most species called cestodes, the neck produces chains of fragments called proglottids through a process called strobilation. Therefore, the more mature pitch is farther from the first pitch. Adult tapeworms that infect humans can form nodal chains over 20 meters long, although 4 meters is more typical. Each section has male and female reproductive organs. If the host's gut contains two or more adults of the same species of tapeworm, they will generally fertilize each other, but segments of the same worm can fertilize each other or even themselves. When the egg is fully developed, the ganglia detach and are excreted by the host. Diphyllobothrium adults infect fish, while larvae use copepod crustaceans as intermediate hosts. 

The excreted segments release their eggs into the water, where the eggs hatch into ciliated swimming larvae. If the larva is swallowed by the copepod, it sheds cilia and the skin becomes syncytia, then the larva enters the blood cavity of the copepod an internal cavity that is the central part of the circulatory system, where it uses three small hooks to support itself. If the fish eat the copepods, the larvae will transform into a small non-segmented tapeworm that penetrates the intestine and becomes an adult. Several tapeworms infect the internal organs of humans, cats, and dogs. Young fish use herbivores such as pigs, cows, and rabbits as intermediate hosts. 

The excreted segments release eggs attached to grass blades, which hatch after being ingested by herbivores. The larva then enters the muscle tissue of the herbivore, where it deforms an oval worm that grows about 10 millimetres and maintains a head segment inside. When the final host eats infected raw meat or undercooked meat from the intermediate host, as the adult tapeworm develops, the worm’s head segment will exit and attach to the intestine. Members of the smaller group called Cestodaria have no heads, produce no knots, and have a body shape similar to diagenesis. Cestodaries live on fish and turtles. 

Human Interactions 

Flatworms in humans are believed to cause many diseases. Cestodes and trematodes can cause diseases in humans and their livestock, and single genes can cause serious population losses in fish farms. Schistosomiasis, also known as schistosomiasis or snail fever, is the second most destructive parasitic disease after malaria in tropical countries. The Carter Center estimates that 200 million people in 74 countries are infected with the disease, and half of the victims live in Africa. The death rate from this disease is very low, but it generally manifests itself as a chronic disease that can damage internal organs. It can affect growth and cognitive development in children and increase the risk of bladder cancer in adults. The disease is caused by several species of flukes of the genus Schistosoma, which can penetrate human skin, those most at risk use infected bodies of water for recreation or laundry. 

In 2000, an estimated 45 million people were infected with beef tapeworm saginata, and 3 million people were infected with pork tapeworm. Adult tapeworm infection of the digestive system can cause abdominal symptoms. Although unpleasant, it rarely causes disability or is life-threatening. However, neurocysticercosis, caused by invasion of the central nervous system by larvae of the porcine tapeworm, is the leading cause of acquired epilepsy worldwide. In 2000, about 39 million people were infected with trematodes, which naturally parasitize fish and crustaceans, but can be transmitted to humans who eat raw or lightly cooked shellfish. Humans infected with the diffuse fish tapeworm Diphyllobothrium latum occasionally cause vitamin B12 deficiency and, in severe cases, can cause megaloblastic anaemia. 

Due to social trends, the threat to humans in developed countries is increasing. The rise of organic agriculture, the use of manure and sewage sludge instead of artificial fertilizers, the spread of parasites directly or through the feces of gulls that feed on manure and mud are causes of disease. Raw or lightly cooked foods are becoming increasingly popular, meat, seafood, and salad greens are imported from high-risk areas and, as a root cause, people's awareness of parasites compared to other public health problems such as reduced contamination. In less developed countries, inadequate sanitation and the use of human feces as fertilizer or fertile fish farm ponds continue to spread parasitic flatworms, while improperly designed irrigation and water supply projects provide additional channels for their reproduction. 

People in these countries often cannot afford the fuel costs needed to cook food enough to kill the parasites. Controlling parasites that infect humans and livestock has become more difficult because many species have developed resistance to drugs that were effective in the past, mainly to kill larvae in meat. Although poorer countries are still battling unintentional infections, the United States has reported cases of intentional infections in dieters eager to lose weight quickly.