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A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase -shaped body. In solitary polyps, the aboral (opposite to oral) end is attached to the substrate by means of a disc-like holdfast called a pedal disc , while in colonies ...
The polyp stage is benthic, with the cells forming colonies, while the medusa stage is a singular, planktonic organism. Generally in hydrozoa the medusa develops from the asexual budding of the polyp and the polyp results from sexual reproduction of medusae. [3] In T. nutricula, planktonic medusa have the capability to bud polyps or medusae ...
The reproductive polyp gonozooids have medusa buds. These medusa buds differentiate Obelia from others in the family Campanulariidae because development begins from a bud within the gonotheca. Eventually the buds are lost, and subsequent development shares resemblances with other hydranths. Other hydranths are specialized for defense.
In hydrozoan species with both polyp and medusa generations, the medusa stage is the sexually reproductive phase. Medusae of these species of Hydrozoa are known as "hydromedusae". Most hydromedusae have shorter lifespans than the larger scyphozoan jellyfish.
Hydrozoans exhibit the greatest variety of life cycles among medusozoans, with either the polyp or the medusa stage being missing in some groups. [4] In general, medusae are budded laterally from polyps, become mature and spawn, releasing gametes into the water. The planulae may settle to become polyps or continue living in the water column as ...
Some, however, omit either the polyp or the medusa stage, and the parasitic classes evolved to have neither form. Cnidarians were formerly grouped with ctenophores, also known as comb jellies, in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla. [6]
O. geniculata have two distinct forms – polyp and medusa, also known as hydranths and gonangia, respectively. [5] The horizontal portion of the hydranth is called the hydrorhiza. [6] The hydrorhiza is the structure that attaches to the other hydranths as well as the substrate.
The man o' war is described as a colonial organism because the individual zooids in a colony are evolutionarily derived from either polyps or medusae, [15] i.e. the two basic body plans of cnidarians. [16] Both of these body plans comprise entire individuals in non-colonial cnidarians (for example, a jellyfish is a medusa, while a sea anemone ...