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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.
Polypodium has traditionally been considered a cnidarian because it possesses nematocysts, the stinging structures characteristic of this phylum. [2] Molecular phylogenetic studies using 18S rDNA sequence data temporarily challenged this interpretation, by finding that Polypodium is a close relative to myxozoans and suggesting that together ...
Cnidarians include corals, sea anemones, jellyfish and hydrozoans. They form a phylum containing over 10,000 [ 32 ] species of animals found exclusively in aquatic (mainly marine) environments. Their bodies consist of mesoglea , a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick .
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.
Ctenophores resemble cnidarians in relying on water flow through the body cavity for both digestion and respiration, as well as in having a decentralized nerve net rather than a brain. Also like cnidarians, the bodies of ctenophores consist of a mass of jelly, with one layer of cells on the outside and another lining the internal cavity. In ...
It is also possible that some humans believe that, they themselves being vertebrates, the group deserves more attention than invertebrates. [62] In any event, in the 1968 edition of Invertebrate Zoology , it is noted that "division of the Animal Kingdom into vertebrates and invertebrates is artificial and reflects human bias in favor of man's ...
Hydra (/ ˈ h aɪ d r ə / HY-drə) is a genus of small freshwater hydrozoans of the phylum Cnidaria.They are native to the temperate and tropical regions. [2] [3] The genus was named by Linnaeus in 1758 after the Hydra, which was the many-headed beast of myth defeated by Heracles, as when the animal has a part severed, it will regenerate much like the mythical hydra's heads.
Sea pens are marine cnidarians belonging to the order Pennatulacea, which are colony-forming benthic filter feeders within the class Octocorallia (subphylum Anthozoa).There are 14 families within the order and 35 extant genera; it is estimated that of 450 described species, around 200 are valid.