Some animals of this group are always polyps, some are always medusae, and some exhibit both a polyp and a medusa stage in their life cycle. The polyp is a sessile, or nonmotile, organism; well-known solitary polyps are the sea anemone and the freshwater hydra.
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The medusa, when free swimming, is popularly known as a jellyfish. Anatomy The two forms are similar in construction; both consist of a cylindrical body surrounding a digestive
Obelia asexual reproduction definition, with a single opening, the mouth, at one end. The mouth is surrounded by tentacles, which are used to capture food and convey it to the mouth; these tentacles are armed with stinging cells which paralyze the prey.
Obelia is a genus of...
The body wall is composed of three layers of tissue. Thin layers called endoderm and ectoderm line the outside and inside, respectively; between these is a layer of jellylike material, called mesoglea, of varying thickness.
The polyp, also called the hydroid, tends to be elongated, with a thin body wall; it is attached to the ocean bottom or other surface by the end opposite the mouth, its tentacles pointing upward. The medusa tends to be rounded, with a thick body wall containing much mesoglea; it swims or is carried in the current with the mouth side down and the tentacles dangling.
Obelia asexual reproduction definition organisms that exhibit both forms, such Obelia asexual reproduction definition members of the cosmopolitan genus Obelia, the polyp is the asexual stage and the medusa the sexual stage.
In such organisms the polyp, by budding, gives rise to medusae, which either detach themselves and swim away or remain permanently attached to the polyp. The medusae then produce new polyps by sexual reproduction. A medusa produces eggs or sperm, which are usually shed into the water; when an egg is fertilized, it develops into a swimming larva, which eventually settles and grows into a polyp.
In addition to this elaborate means of reproduction, the polyp can form new polyps by budding. In some
Obelia asexual reproduction definition of coelenterates either the polyp "Obelia asexual reproduction definition" the medusa has become highly developed, with the reduction or complete loss of the other form. Obelia is a tree-like branched,...
Where only the medusa occurs, as in many jellyfish, the larva never settles, and grows directly into a medusa. Where only the polyp exists, as in the hydra and the sea anemonethe organism has the ability to produce new polyps sexually, as
Obelia asexual reproduction definition as by budding.
Colonial Species In many species
Obelia asexual reproduction definition polyp, or hydroid, stage is colonial: The branching, hydroid colonies of Obelia are commonly found on North American seashores; the individual polyps are microscopic, but the feathery white or yellow colony grows up to 12 in. Individual polyps project from the branches of such a colony; they produce the tiny, free-swimming Obelia medusae, barely visible to the naked eye.
Other hydroid colonies are colonial coral and the sea pens ; these have no medusa stage. All hydroid colonies have at least two types of individual polyps, specialized for feeding and reproduction respectively; some have additional specialized types. The purple sail, genus Vellela, and the Portuguese man-of-war, genus Physalia, are elaborate floating colonies composed of many types of specialized individuals, both polyplike and medusalike in structure; the entire colony is equipped with a float.
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Polyps are commonly found in the nose and sinuses, giving rise to obstruction, chronic infection, and discharge. Other sites include the ear, the stomach, and the colon, where they may eventually become malignant. Polyps are usually removed surgically see polypectomy. Most juvenile polyps are benign.
However, the definition of adult...
See also Peutz-Jeghers syndrome. In some species, polyps are a phase in the life cycle that alternates with a medusoid phase. Hydra are single; others e. Polyps typically reproduce asexually by budding to form either new polyps or medusae. The latter reproduce sexually giving rise to new polyps.
The Obelia is a trimorphic...
Sea anemones are solitary polyps that reproduce sexually to form new polyps. It has a mouth surrounded by extensible tentacles, and a lower end that is adapted for attachment to a surface.
The Obelia life cycle begins...
It is distinct from the free-swimming medusa. It may be solitary, as in the sea anemonebut is more often an individual of a colonial organism such as coral.
In Siphonophora the polyp has been modified for a pelagiccolonial existence. Home Plants and Animals Animals Zoology: Invertebrates polyp and medusa. Print this article Print all entries for this topic Cite this article.
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Obelia asexual reproduction definition. Learn more about citation styles Citation styles Encyclopedia. Modern Language Association http: However, the definition of adult and larval stages in leptolids is a matter of debate (see. A common form of asexual reproduction in hydroids is the formation of.
The Obelia life cycle begins as immobile polyp colonies that contain digestive hydranth and reproductive gonangium units. The medusa, or jellyfish, swim freely and reproduce sexually, releasing eggs and sperm into the "Obelia asexual reproduction definition." These animals belong to the class Hydrozoa and phylum. Obelia: Obelia, genus of invertebrate marine animals of the class Hydrozoa ( phylum Cnidaria).
The genus, widely The polyp asexually produces medusae, or jellyfish. Obelia medusae release sperm or reproduction: Life cycles of animals.
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