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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 ...
This consists of a tubular column topped by a flattened area, the oral disc, with a central mouth; a whorl of tentacles surrounds the mouth. In solitary individuals, the base of the polyp is the foot or pedal disc, which adheres to the substrate, while in colonial polyps, the base links to other polyps in the colony. [2] Anatomy of a stony ...
The polyp stage closely resembles Hydra. The medusae are active swimmers that propel themselves upward in the water column by rhythmic pulsations of the bell. Upon reaching the surface, the bell relaxes, the tentacles become fully extended, and any small fish or crustaceans encountered as the medusae slowly drift toward the bottom are ensnared.
The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mouth is fringed with tentacles. Although some species are solitary, most are colonial. The founding polyp settles and starts to secrete calcium carbonate to protect its soft body. Solitary corals can be as much as 25 cm (10 in) across but ...
The polyps are connected by epidermis which surrounds a gastrovascular cavity. The epidermis secretes a chitinous skeleton which supports the stem and in some hydroids, the skeleton extends into a cup shape surrounding the polyp. Most of the polyps are gastrozooids or feeding polyps, but some are specialised reproductive structures known as ...
Strobilation tend to occur at specific periods, typically early spring. As ephyra size remains constant regardless of the polyp size, larger polyps produce more numerous ephyras. Some scyphozoans, such as Nausithoe aurea, cnidarians also strobilate in their solitary polyp form, producing either ephyra or planuloids.
Species are generally solitary marine animals capable of benthic locomotion. [3] [4] These corals often appear to be bleached or dead. [5] In most genera, a single polyp emerges from the center of the skeleton to feed at night. Most species remain fully detached from the substrate in adulthood. Some are immobile as well as colonial. [6] [7]
Scolymia lacera is a coral with a single, solitary polyp and does not increase in size by budding as do colonial species of coral. It is a small species with a diameter of up to 6 centimetres (2.4 in). The radially-running ridges in the stony cup which it secretes can be seen through the fleshy body of the polyp.