The flatworms, flat worms, Platyhelminthes, or platyhelminths are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Unlike other bilaterians, they are acoelomates, and have no specialised circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. The digestive cavity has only one opening for both ingestion and egestion ; as a result, the food cannot be processed continuously.
Taenia solium, the pork tapeworm, belongs to the cyclophyllid cestode family Taeniidae. It is found throughout the world and is most common in countries where pork is eaten. It is a tapeworm that uses humans as its definitive host and pigs as the intermediate or secondary hosts. It is transmitted to pigs through human feces that contain the parasite eggs and contaminate their fodder. Pigs ingest the eggs, which develop into larvae, then into oncospheres, and ultimately into infective tapeworm cysts, called cysticercus. Humans acquire the cysts through consumption of uncooked or under-cooked pork and the cysts grow into an adult worms in the small intestine.
Pseudophyllid cestodes are tapeworms with multiple "segments" (proglottids) and two bothria or "sucking grooves" as adults. Proglottids are identifiably pseudophyllid as the genital pore and uterine pore are located on the mid-ventral surface, and the ovary is bilobed ("dumbbell-shaped").
Tapeworms of the order Cyclophyllidea are the most important cestode parasites of humans and domesticated animals. All have multiple proglottid "segments", and all have four suckers on their scolices (heads), though some may have other structures, as well. Proglottids of this order have genital openings on one side, and a compact yolk gland or vitellarium posterior to the ovary.
Taenia is the type genus of the Taeniidae family of tapeworms. It includes some important parasites of livestock. Members of the genus are responsible for taeniasis and cysticercosis in humans, which are types of helminthiasis belonging to the group of neglected tropical diseases. More than 100 species are recorded. They are morphologically characterized by a ribbon-like body composed of a series of segments called proglottids; hence the name Taenia. The anterior end of the body is the scolex. Some members of the genus Taenia have an armed scolex ; of the two major human parasites, Taenia saginata has an unarmed scolex, while Taenia solium has an armed scolex.
Echinococcus granulosus, also called the hydatid worm, hyper tape-worm or dog tapeworm, is a cyclophyllid cestode that dwells in the small intestine of canids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes cystic echinococcosis, also known as hydatid disease. The adult tapeworm ranges in length from 3 mm to 6 mm and has three proglottids ("segments") when intact—an immature proglottid, mature proglottid and a gravid proglottid. The average number of eggs per gravid proglottid is 823. Like all cyclophyllideans, E. granulosus has four suckers on its scolex ("head"), and E. granulosus also has a rostellum with hooks. Several strains of E. granulosus have been identified, and all but two are noted to be infective in humans.
Dipylidium caninum, also called the flea tapeworm, double-pored tapeworm, or cucumber tapeworm is a cyclophyllid cestode that infects organisms afflicted with fleas and canine chewing lice, including dogs, cats, and sometimes human pet-owners, especially children.
The Hymenolepididae are family of cyclophyllid tapeworms. Their characteristic feature is the small number of testes. The unilateral genital pores and large external seminal vesicle allow for easy recognition. Most species are small, transparent, and easy to study. The family contains over 90 genera with over 900 species, having as their definitive host birds or mammals. Most reside in the intestines of their definitive hosts. The majority of species with known lifecycles have arthropods as intermediate hosts.
Dwarf tapeworm is a cosmopolitan species though most common in temperate zones, and is one of the most common cestodes infecting humans, especially children.
Taenia pisiformis, commonly called the rabbit tapeworm, is an endoparasitic tapeworm which causes infection in lagomorphs, rodents, and carnivores. Adult T. pisiformis typically occur within the small intestines of the definitive hosts, the carnivores. Lagomorphs, the intermediate hosts, are infected by fecal contamination of grasses and other food sources by the definitive hosts. The larval stage is often referred to as Cysticercus pisiformis and is found on the livers and peritoneal cavities of the intermediate hosts. T. pisiformis can be found worldwide.
Hymenolepis is a genus of cyclophyllid tapeworms that cause hymenolepiasis. They parasitise mammals, including humans. Some notable species are:
Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of many similar units known as proglottids—essentially packages of eggs which are regularly shed into the environment to infect other organisms. Species of the other subclass, Cestodaria, are mainly fish infecting parasites.
Bothriocephalus acheilognathi, also known as the Asian tapeworm, is a freshwater fish parasite that originated from China and Eastern Russia. It is a generalized parasite that affects a wide variety of fish hosts, particularly cyprinids, contributing to its overall success.
Raillietina is a genus of tapeworms that includes helminth parasites of vertebrates, mostly of birds. The genus was named in 1920 in honour of a French veterinarian and helminthologist, Louis-Joseph Alcide Railliet. Of the 37 species recorded under the genus, Raillietina demerariensis, R. asiatica, and R. formsana are the only species reported from humans, while the rest are found in birds. R. echinobothrida, R. tetragona, and R. cesticillus are the most important species in terms of prevalence and pathogenicity among wild and domestic birds.
Raillietina echinobothrida is a parasitic tapeworm belonging to the class Cestoda. It is the most prevalent and pathogenic helminth parasite in birds, particularly in domestic fowl, Gallus domesticus Linnaeus, 1758. It requires two hosts, birds and ants, for completion of its life cycle. It is a hermaphrodite worm having both the male and female reproductive organs in its body. The parasite is responsible for 'nodular tapeworm disease' in poultry.
Raillietina tetragona is a parasitic tapeworm belonging to the class Cestoda. It is a cosmopolitan helminth of the small intestine of pigeon, chicken and guinea fowl, and is found throughout the world.
Raillietina cesticillus is a parasitic tapeworm of the family Davaineidae. Sometimes called 'broad-headed tapeworm', it infects the small intestine of chicken and occasionally other birds, such as guinea fowl and turkey, which are generally in close proximity to backyard poultry. It is a relatively harmless species among intestinal cestodes in spite of a high prevalence. In fact it probably is the most common parasitic platyhelminth in modern poultry facilities throughout the world.
The Anoplocephalidae are a family of tapeworms containing the genera Bertiella, Anoplocephala, Paranoplocephala, Moniezia, and others.
Diphyllobothriidae is a family of Cestoda (tapeworms). Members of this family are gut parasites of vertebrates. In most species the definitive hosts are marine or aquatic mammals such as cetaceans and pinnipeds, the first intermediate host usually being a crustacean and the second intermediate a fish. The genus Diphyllobothrium is found as an adult in mammals and fish-eating birds, including the domestic cat. The genus Spirometra tends to have a land-dwelling or semi-aquatic vertebrate as its second intermediate host, with the adults usually occurring in felines.
Tetragonoporus is a genus of cestodes in the order Pseudophyllidea. It is a monotypic genus, and the only species is Tetragonoporus calyptocephalus, previously known as Polygonoporus giganticus. This tapeworm is a gut parasite of whales.
