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Cestodes are parasites of vertebrates, with each species infecting a single definitive host or group of closely related host species. All but amphilinids and gyrocotylids (which burrow through the gut or body wall to reach the coelom [ 6 ] ) are intestinal, though some life cycle stages rest in muscle or other tissues.
These can be categorized into three groups; cestodes, nematodes and trematodes.Examples include: Acanthocephala; Ascariasis (roundworms); Cestoda (tapeworms) including: Taenia saginata (human beef tapeworm), Taenia solium (human pork tapeworm), Diphyllobothrium latum (fish tapeworm) and Echinococcosis (hydatid tapeworm)
Trematodes are covered by a tegument, that protects the organism from the environment by providing secretory and absorptive functions. The life cycle of a typical trematode begins with an egg . Some trematode eggs hatch directly in the environment (water), while others are eaten and hatched within a host, typically a mollusc .
Cyclophyllidea (the cyclophyllid cestodes) is the order of Cestoda (tapeworm).It is the largest and most diverse order of Cestoda (tapeworm), encompassing species that infect all classes of terrestrial tetrapods including humans and domesticated animals, [1] and includes species with some of the most severe health impact on wildlife, livestock, and humans.
Adult trematodes lay smaller numbers of eggs compared to cestodes or nematodes. However, the egg develops into a miracidia from which thousands of cercariae, or swimming larvae, develop. This means that one egg may produce thousands of adult worms. [15]
Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts . The intermediate host, in which asexual reproduction occurs, is usually a snail .
The fine structure of tegument is essentially the same in both the cestodes and trematodes. A typical tegument is 7-16 μm thick, with distinct layers. It is a syncytium consisting of multinucleated tissues with no distinct cell boundaries. The outer zone of the syncytium, called the "distal cytoplasm," is lined with a plasma membrane.
Nematode eggs from the clades Ascaridina, Spirurina, and Trichocephalida have been discovered in coprolites from the Oligocene-aged Tremembé Formation, which represented a palaeolake in present-day São Paulo with a diverse fossil assemblage of birds, fish, and arthropods that lent itself to fostering high nematode diversity. [41]