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dcdaDca. 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.
Hydra, a genus belonging to Cnidaria, is used as a model organism to study nerve nets. In the body column of Hydra, there is continuous division of epithelial cells occurring while the size of the Hydra remains constant. The movement of individual neurons is coupled to the movement of epithelial cells. Experiments have provided evidence that ...
a Beroe ovata, b unidentified cydippid, c "Tortugas red" cydippid, d Bathocyroe fosteri, e Mnemiopsis leidyi, and f Ocyropsis sp. [17]. Among animal phyla, the ctenophores are more complex than sponges, about as complex as cnidarians (jellyfish, sea anemones, etc.), and less complex than bilaterians (which include almost all other animals).
Increased habitat and task complexity has favored the high-resolution visual systems common in derived cnidarians such as box jellyfish. [40] Basal visual systems observed in various cnidarians exhibit photosensitivity representative of a single task or behavior. Extraocular photoreception (a form of non-directional photoreception), is the most ...
Coelenterata is a term encompassing the animal phyla Cnidaria (corals, true jellies, sea anemones, sea pens, and their relatives) and Ctenophora (comb jellies). The name comes from Ancient Greek κοῖλος (koîlos) 'hollow' and ἔντερον (énteron) 'intestine', referring to the hollow body cavity common to these two phyla.
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.
Drawing of the statocyst system Statocysts (ss) and statolith (sl) inside the head of sea snail Gigantopelta chessoia. The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, [1] cnidarians, [2] ctenophorans, [3] echinoderms, [4] cephalopods, [5] [6] crustaceans, [7] and gastropods, [8] A similar structure is also found in Xenoturbella. [9]
Each rhopalium also has two pit eyes on either side of the upper lens eye which likely act as mere light meters, and two slit eyes on either side of the lower lens eye which are likely used to detect vertical movement. [16] In total, the box jellyfish have six eyes on each of their four rhopalia, creating a total of 24 eyes.