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Hydra (/ ˈ h aɪ d r ə / HY-drə) is a genus of small freshwater hydrozoans of the phylum Cnidaria.They are solitary, carnivorous jellyfishlike animals [2], native to the temperate and tropical regions.
The medusae of hydrozoans are smaller than those of typical jellyfish, ranging from 0.5 to 6 cm (0.20 to 2.36 in) in diameter. Although most hydrozoans have a medusoid stage, this is not always free-living and in many species exists solely as a sexually reproducing bud on the surface of the hydroid colony.
Cubozoa is a group commonly known as box jellyfish, that occur in tropical and warm temperate seas. They have cube-shaped, transparent medusae and are heavily-armed with venomous nematocysts. Cubozoans have planula larvae, which settle and develop into sessile polyps, which subsequently metamorphose into sexual medusae, [ 11 ] the oral end of ...
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 ...
Upon reaching adult size, jellyfish spawn regularly if there is a sufficient supply of food. In most species, spawning is controlled by light, with all individuals spawning at about the same time of day; in many instances this is at dawn or dusk. [66] Jellyfish are usually either male or female (with occasional hermaphrodites).
This is an accepted version of this page This is the latest accepted revision, reviewed on 3 February 2025. Species of small, biologically immortal jellyfish Immortal jellyfish Turritopsis dohrnii medusa Scientific classification Domain: Eukaryota Kingdom: Animalia Phylum: Cnidaria Class: Hydrozoa Order: Anthoathecata Family: Oceaniidae Genus: Turritopsis Species: T. dohrnii Binomial name ...
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.
Hydra vulgaris (fresh-water polyp) 5,600 [15] Megaphragma mymaripenne: 7,400 [16] Box jellyfish: ... One early suggestion was brain size (or weight, which provides ...