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Gorgonian polyps in a reef aquarium

A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are approximately cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral end is attached to the substrate by means of a disc-like holdfast called the pedal disc, while in colonies of polyps it is connected to other polyps, either directly or indirectly. The oral end contains the mouth, and is surrounded by a circlet of tentacles.

Classes[edit]

In the class Anthozoa, comprising the sea anemones and corals, the individual is always a polyp; in the class Hydrozoa, however, the individual may be either a polyp or a medusa, with most species undergoing a life cycle with both a polyp stage and a medusa stage. In class Scyphozoa, the medusa stage is dominant, and the polyp stage may or may not be present, depending on the family. In those scyphozoans that have the larval planula metamorphose into a polyp, the polyp, also called a "scyphistoma," grows until it develops a stack of plate-like medusae that pinch off and swim away in a process known as strobilation. Once strobilation is complete, the polyp may die, or regenerate itself to repeat the process again later. With Cubozoans, the planula settles onto a suitable surface, and develops into a polyp. The cubozoan polyp then eventually metamorphoses directly into a Medusa.

Anatomy[edit]

Anatomy of a coral polyp.

The body of the polyp may be roughly compared in a structure to a sac, the wall of which is composed of two layers of cells. The outer layer is known technically as the ectoderm, the inner layer as the endoderm (or gastroderm). Between ectoderm and endoderm is a supporting layer of structureless gelatinous substance termed mesogloea, secreted by the cell layers of the body wall. The mesogloea may be a very thin layer, or may reach a fair thickness, and then sometimes contains skeletal elements formed by cells which have migrated into it from the ectoderm.

The sac-like body built up in this way is attached usually to some firm object by its blind end, and bears at the upper end the mouth which is surrounded by a circle of tentacles which resemble glove fingers. The tentacles are organs which serve both for the tactile sense and for the capture of food. Polyps extend their tentacles, particularly at night, containing coiled stinging nettle-like cells or nematocysts which pierce and poison and firmly hold living prey paralysing or killing them. Polyp prey includes copepods and fish larvae.[1] Longitudinal muscular fibrils formed from the cells of the ectoderm allow tentacles to contract when conveying the food to the mouth. Similarly, circularly disposed muscular fibrils formed from the endoderm permit tentacles to be protract or thrust out once they are contracted. These muscle fibres belong to the same two systems, thus allows the whole body to retract or protrude outwards.

We can distinguish therefore in the body of a polyp the column, circular or oval in section, forming the trunk, resting on a base or foot and surmounted by the crown of tentacles, which enclose an area termed the peristome, in the centre of which again is the mouth. As a rule there is no other opening to the body except the mouth, but in some cases excretory pores are known to occur in the foot, and pores may occur at the tips of the tentacles. Thus it is seen that a polyp is an animal of very simple structure, a living fossil that has not changed significantly for about half a billion years (per generally accepted dating of Cambrian sedimentary rock).

The external form of the polyp varies greatly in different cases. The column may be long and slender, or may be so short in the vertical direction that the body becomes disk-like. The tentacles may number many hundreds or may be very few, in rare cases only one or two. They may be long and filamentous, or short and reduced to mere knobs or warts. They may be simple and unbranched, or they may be feathery in pattern. The mouth may be level with the surface of the peristome, or may be projecting and trumpet-shaped. As regards internal structure, polyps exhibit two well-marked types of organization, each characteristic of one of the two classes, Hydrozoa and Anthozoa.

In the class Hydrozoa, the polyps are indeed often very simple, like the common little freshwater 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 the mesenteries project into the enteric cavity but some extend from the body wall to the central stomodaeum.

Reproduction[edit]

It is an almost universal attribute of polyps to reproduce asexually by the method of budding. This mode of reproduction may be combined with sexual reproduction, or may be the sole method by which the polyp produces offspring, in which case the polyp is entirely without sexual organs. In many cases the buds formed do not separate from the parent but remain in continuity with it, thus forming colonies or stocks, which may reach a great size and contain a vast number of individuals. Slight differences in the method of budding produce great variations in the form of the colonies. The reef-building corals are polyp-colonies, strengthened by the formation of a firm skeleton.

Etymology[edit]

The name polyp was given by René Antoine Ferchault de Réaumur[2] to these organisms from their superficial resemblance to an octopus (Fr. poulpe, ultimately from Greek adverb πολύ (poly, "much") + noun πούς (pous, "foot")), with its circle of writhing arms round the mouth. This comparison contrasts to the common name "coral-insects" applied to the polyps which form coral.

See also[edit]

Notes[edit]

  1. ^ Chang, T.D. and Sullivan, J.M. "Temporal associations of coral and zooplankton activity on a Caribbean reef" Dartmouth Studies in Tropical Ecology. 2008. Accessed 2009-06-21.
  2. ^ Stott, Rebecca. "Darwin's ghosts: the secret history of evolution" New York, Spiegel & Grau (2012). ISBN 9781400069378

References[edit]

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Polyp — Please support Wikipedia.
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497 news items

Medscape

Medscape
Fri, 21 Mar 2014 10:03:45 -0700

"This RCT provides strong evidence to suggest that hysteroscopic morcellation is quicker to perform, more successful at completing polyp removal, less painful, and more acceptable to women than traditional electrosurgical resection for the removal of ...

BioNews Texas

KSBY San Luis Obispo News
Thu, 03 Apr 2014 04:54:10 -0700

That's because adenomas, a type of polyp, can be removed and prevent cancers from developing. Researchers say early detection through regular colonoscopies can help reduce rates of colorectal cancer, which is the second leading cause of cancer deaths ...
 
KESQ
Thu, 17 Apr 2014 19:03:45 -0700

Colorectal cancer is the third-leading cancer among men and women, and is defined as when malignant cells in the large intestine grow out of control, usually as a non-cancerous polyp. Over years, polyps can develop into a no-longer disguised, deadly ...
 
Baystreet.ca
Sat, 05 Apr 2014 05:11:15 -0700

Carol A. Burke, MD, Director, Center for Colon Polyp and Cancer Prevention, Department of Gastroenterology and Hepatology, Cleveland Clinic, Cleveland, OH, presented on Polyposis Syndromes and Guidelines for Colon Cancer Screening. Glendale, CA ...

Salon

Salon
Wed, 16 Apr 2014 16:08:46 -0700

He sounded somber, and went on to explain that the kind of precancerous polyp he'd removed, and the place where he'd found it, were both indicative of a highly aggressive form of colon cancer. The polyp was also very difficult to see and could easily ...

Philly.com

Shelbyville Times-Gazette
Tue, 25 Mar 2014 07:26:15 -0700

A polyp isn't necessarily cancerous -- but there's one type of polyp, an adenomapous polyp, which can become cancerous later if it isn't removed now. Most colon cancer starts out as adenomapous polyps, said Monajjem. The good news is that the death ...

IPWatchdog.com

IPWatchdog.com
Thu, 17 Apr 2014 05:11:15 -0700

This increases access to virtual radiology techniques, which are often superior to conventional colonoscopy techniques for polyp detection. U.S Patent No. 8686851, issued under the title System and Method for Rapid Location of an Alarm Condition ...
 
Wauwatosa Now
Sun, 30 Mar 2014 09:32:10 -0700

While not every colon polyp turns to cancer, almost every colon cancer begins as a small non-cancerous polyp. During a colonoscopy these polyps can be identified and removed or destroyed. If a polyp is large enough, tissue can be retrieved and sent for ...
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