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Platyhelminthes (from the Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning "worm") [4] is a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates commonly called flatworms or flat worms.
The mouth is located in the middle of the underside of the body, which is covered with hairlike projections (cilia). There are no circulatory or respiratory systems; oxygen enters and carbon dioxide leaves the planarian's body by diffusing through the body wall.
Tegument / ˈ t ɛ ɡ j ʊ m ə n t / is a term in helminthology for the outer body covering of members of the phylum Platyhelminthes. The name is derived from a Latin word tegumentum or tegere, meaning "to cover". [1] [2] It is characteristic of flatworms including the broad groups of tapeworms and flukes.
They include hugely varied body plans. Many have fluid-filled, hydrostatic skeletons, like jellyfish or worms. Others have hard exoskeletons, outer shells like those of insects and crustaceans. The most familiar invertebrates include the Protozoa, Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Echinodermata, Mollusca and Arthropoda.
The gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Coelenterates or cnidarians (including jellyfish and corals) and Platyhelminthes (flatworms). The cavity may be extensively branched into a system of canals.
The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes (flatworms), and include all the sub-groups that are not exclusively parasitic.There are about 4,500 species, which range from 1 mm (0.039 in) to large freshwater forms more than 500 mm (20 in) long [3] or terrestrial species like Bipalium kewense which can reach 600 mm (24 in) in length.
Digeneans possess a vermiform, unsegmented body-plan and have a solid parenchyma with no body cavity as in all platyhelminths. Anterior sucker of Overstreetia cribbi a zoogonid digenean [ 1 ] There are typically two suckers , an anterior oral sucker surrounding the mouth , and a ventral sucker sometimes termed the acetabulum , on the ventral ...
Pseudoceros are simultaneous hermaphrodites [9] and reproduce sexually via random hypodermic insemination through the body tissue. [10] These organisms participate in penis fencing, [9] which is a behavior where the flatworms use their extended penises to stab and inseminate the other, while avoiding becoming inseminated themselves.