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Cnidarians range in size from a mere handful of cells for the parasitic myxozoans [31] through Hydra's length of 5–20 mm (1 ⁄ 4 – 3 ⁄ 4 in), [40] to the lion's mane jellyfish, which may exceed 2 m (6 ft 7 in) in diameter and 75 m (246 ft) in length. [41] Prey of cnidarians ranges from plankton to animals several times larger than ...
Hydra generally react in the same way regardless of the direction of the stimulus, and this may be due to the simplicity of the nerve nets. Hydra are generally sedentary or sessile, but do occasionally move quite readily, especially when hunting. They have two distinct methods for moving – 'looping' and 'somersaulting'.
Polypodium was long considered a unique intracellular parasite among cnidarians. [6] [7] Its hosts include 14 species of Acipenser, 2 species of Huso, Polyodon spathula [6] and Scaphirhynchus platorynchus. [2] Polypodium hydriforme is an endocellular parasite with an unusual life cycle, a peculiar morphology, and high rates of DNA evolution.
Hydrozoa (hydrozoans; from Ancient Greek ὕδωρ (húdōr) 'water' and ζῷον (zôion) 'animal') is a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water.
Hydra viridissima is a species of cnidarian which is commonly found in still or slow-moving freshwater [2] in the Northern temperate zone. Hydra viridissima is commonly called green hydra due to its coloration, which is due to the symbiotic green algae Chlorella vulgaris which live within its body. [ 3 ]
Like other hydras, Hydra vulgaris cling to a base object with a "foot" pad, shaped like a disk. The Hydra moves by releasing its grip on its base and is carried away by the current. H. vulgaris can also move by bending over, grabbing a surface with its tentacles, releasing its grip with its "foot" and flipping over itself.
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known and heavily discussed group. It has also been called Gymnoblastea and (with or without an emended ending -ae), Anthomedusa, Athecata, Hydromedusa, and Stylasterina.
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]