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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.
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
Humans make use of many other animal species for food (including meat, eggs, and dairy products), ... catching small prey with its nematocysts as modern cnidarians do.
Although freshwater is an unusual habitat for cnidarians, it is not unheard of, especially within hydrozoans. [2] For instance, the model organism Hydra and the jellyfish Craspedacusta sowerbii are both exclusively freshwater hydrozoans. [2] Hydra and Craspedacusta sowerbii are distantly related and are not closely related to Polypodium.
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]
Apple snails use the siphon in a way that is reminiscent of a human swimmer using a snorkel, except that the apple snail's siphon can be retracted completely, or extended to various lengths as needed. [6] For these freshwater snails, the siphon is an anti-predator adaptation.
Anthozoa is a class of marine invertebrates which includes sessile cnidarians such as the sea anemones, stony corals, soft corals and sea pens.Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as planktons.