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Pacific sea nettles, Chrysaora fuscescens. Cnidaria (/ n ɪ ˈ d ɛər i ə, n aɪ-/ nih-DAIR-ee-ə, NY-) [4] is a phylum under kingdom Animalia containing over 11,000 species [5] of aquatic invertebrates found both in fresh water and marine environments (predominantly the latter), including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites.
Although they have large amounts of venom deadly to their prey, their stings and venom are not harmful to humans. They are actually known to be eaten by humans located mostly in Japan and China. The dish is a delicacy in the Japanese and Chinese cultures. This particular species of jellyfish is used also used for medicinal purposes for humans. [8]
Siphonophorae (from Greek siphōn 'tube' + pherein 'to bear' [2]) is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria.According to the World Register of Marine Species, the order contains 175 species described thus far.
Cnidarians, like this starlet sea anemone, are the simplest animals to organise cells into tissue. Yet they have the same genes that form the vertebrate (including human) head. Cnidarians (from Greek for nettle) are distinguished by the presence of stinging cells, specialized cells that they
Like other cnidarians they possess cnidocysts, which were referred to as "polar capsules" before the discovery that myxozoans are cnidarians. These cnidocysts fire tubules as in other cnidarians; some inject substances into the host. However, the tubules lack hooks or barbs, and in some species are more elastic than in other cnidarians.
Cnidarians have huge numbers of cnidocytes on their tentacles. In medusoid form , the body floats on water so that the tentacles hang down in a ring around the mouth. In polyp form, such as sea anemone and coral, the body is below with the tentacles pointed upwards.
Polypodium is a genus of cnidarians that parasitizes in the eggs of sturgeon and similar fishes (Acipenseridae and Polyodontidae). [2] It is one of few animals that lives inside the cells of other animals. Polypodium hydriforme is the only species of this monotypic genus.
Hence ctenophores and cnidarians have traditionally been labelled diploblastic. [18] [20] Both ctenophores and cnidarians have a type of muscle that, in more complex animals, arises from the middle cell layer, [21] and as a result some recent text books classify ctenophores as triploblastic, [22] while others still regard them as diploblastic. [18]