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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 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.
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.
Diagram of a typical insect leg The typical and usual segments of the insect leg are divided into the coxa, one trochanter , the femur, the tibia, the tarsus, and the pretarsus . The coxa in its more symmetrical form, has the shape of a short cylinder or truncate cone, though commonly it is ovate and may be almost spherical.
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 ]
Hydra oligactis, also known as the brown hydra, is a species of hydra found widely dispersed in the northern temperate zone. It is a common organism found in still waters from early Spring to late Autumn. It is commonly found attached to the stems of water plants, the undersides of leaves, submerged twigs and on the surface of stones. When ...
Biological symmetry can be thought of as a balanced distribution of duplicate body parts or shapes within the body of an organism. Importantly, unlike in mathematics, symmetry in biology is always approximate. For example, plant leaves – while considered symmetrical – rarely match up exactly when folded in half.
In the class Hydrozoa, the polyps are indeed often very simple, like the common little fresh water species of the genus Hydra. Anthozoan polyps, including the corals and sea anemones, are much more complex due to the development of a tubular stomodaeum leading inward from the mouth and a series of radial partitions called mesenteries. Many of ...
Harmless or parasitic bacteria may grow on the body or stalk, appearing as part of the morphology of the cell. [5] Inside, there is a curved, transverse macronucleus and round micronucleus near it. The similar genus Pseudovorticella is practically indistinguishable from Vorticella under most conditions.