Polypodium+hydriforme


 * Common Names:** Its scientific name is its only name.
 * Scientific Name:** //Polypodium hydriforme//
 * Phyla:** Cnidaria
 * Class:** Polypodoizoa
 * Description of Habitat:** Freshwater
 * Life Cycle of Animal:** //Polypodium hydriforme// is an endocellular parasite whose unusual life cycle, peculiar morphology, and high rates of DNA evolution, have led to much controversy regarding its phylogenetic position within metazoans. //Polypodium// spends most of its life inside the oocytes of acipenseriform fishes (sturgeons and paddlefish). During this time, //Polypodium// develops from a binucleate cell into an inside-out planuliform larva and then into an elongate inside-out stolon; the epidermal cell layer is located internal to the body and the gastrodermis is located externally. The embryo, larva and stolon are surrounded by a protective polyploid cell, which also functions in digestion. Just prior to host spawning, //Polypodium// everts to the normal position of cell layers, revealing tentacles scattered along the stolon. During eversion, the yolk of the host oocyte fills the gastral cavities of the parasite, supplying the future free-living stage with nutrients. Finally, upon emerging from the host egg in fresh water, the free-living stolon fragments into individual medusoid-like forms that go on to multiply by means of longitudinal fission, form sexual organs, and ultimately infect host fish with their gametophores.




 * Interesting Facts:**
 * //Polypodium// should be placed in its own cnidarian class, Polypodiozoa.
 * Although the fresh water habitat of //Polypodium// is unusual for cnidarians, it is not unheard of, especially within hydrozoans. For instance, the model organism //Hydra// and the jellyfish //Craspedacusta// are both exclusively fresh-water hydrozoans.
 * Although //Polypodium// is the only known intracellular cnidarian parasite, other cnidarians have adopted parasitic life-styles. For example, parasites belonging to the Narcomedusae (Hydrozoa) have been reported to live in the stomach cavities of other narcomedusae and anthomedusae.


 * Zookeeper James K. Kanthachack**

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