Polyp (zoology)

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Gorgonian polyps in a reef aquarium Polypen einer Gorgonie.jpg
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 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 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.



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, [1] 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 of a coral polyp Coral polyp.jpg
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 mesoglea, secreted by the cell layers of the body wall. [1] The mesoglea can be thinner than the endoderm or ectoderm or comprise the bulk of the body as in larger jellyfish. The mesoglea can contain skeletal elements derived from cells migrated from 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. [1] 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. [2] 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. [1]

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, [1] 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. [1]

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 the mesenteries project into the enteric cavity but some extend from the body wall to the central stomodaeum.


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. [1]

Asexual reproduction

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. [1]

Sexual reproduction

Among sea anemones, sexual plasticity may occur. That is, asexually produced clones derived from a single founder individual can contain both male and female individuals (ramets). [3] When eggs and sperm (gametes) are formed, they can produce zygotes derived from “selfing” (within the founding clone) or out-crossing, that then develop into swimming planula larvae.

Polyps of a colony of Cnidaria Polyps of Cnidaria colony.jpg
Polyps of a colony of Cnidaria

The overwhelming majority of stony coral ( Scleractinia ) taxa are hermaphroditic in their adult colonies. [4] In these species, there is ordinarily synchronized release of eggs and sperm into the water during brief spawning events. [5] Although some species are capable of self-fertilization to varying extents, cross-fertilization appears to be the dominant mating pattern. [4]


The name polyp was given by René Antoine Ferchault de Réaumur [6] to these organisms from their superficial resemblance to an octopus (French : poulpe, ultimately from Ancient 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. [1]


75% of the world's corals are threatened [7] due to overfishing, destructive fishing, coastal development, pollution, thermal stress, ocean acidification, crown-of-thorns starfish, and introduced invasive species. [8]

In recent decades the conditions that corals and polyps have found themselves in have been changing, leading to new diseases being observed in corals in many parts of the world, posing even greater risk to an already pressured animal. [9] Aquatic life has been put under a substantial amount of stress because of the pollutants caused by land-based agriculture. Particularly, exposure to the insecticide profenofos and the fungicide MEMC have played a major part in polyp retraction and biomass decrease. [10] [11] There have been many experiments resulting supporting hypothesis that heat stress in Acropora tenuis juvenile polyp provoke an up-regulation of protein in the endoplasmic reticulum. The results vary based on the polyp characteristics such as age, type, and growth stage.

See also


  1. 1 2 3 4 5 6 7 8 9 Wikisource-logo.svg One or more of the preceding sentences incorporates text from a publication now in the public domain : Minchin, Edward Alfred (1911). "Polyp". In Chisholm, Hugh (ed.). Encyclopædia Britannica . 22 (11th ed.). Cambridge University Press. p. 37.
  2. Chang, T.D. and Sullivan, J.M. "Temporal associations of coral and zooplankton activity on a Caribbean reef Archived 2011-06-06 at the Wayback Machine " Dartmouth Studies in Tropical Ecology. 2008. Accessed 2009-06-21.
  3. Schlesinger A, Kramarsky-Winter E, Rosenfeld H, Armoza-Zvoloni R, Loya Y (2010). "Sexual plasticity and self-fertilization in the sea anemone Aiptasia diaphana". PLOS ONE. 5 (7): e11874. Bibcode:2010PLoSO...511874S. doi: 10.1371/journal.pone.0011874 . PMC   2912375 . PMID   20686700.
  4. 1 2 Heyward AJ, Babcock, RC (1986). Self- and cross-fertilization in scleractinian corals. Marine Biology 90, 191-195
  5. Harrison PL, Babcock RC, Bull GD, Oliver JK, Wallace CC, Willis BL (March 1984). "Mass spawning in tropical reef corals". Science. 223 (4641): 1186–9. Bibcode:1984Sci...223.1186H. doi:10.1126/science.223.4641.1186. PMID   17742935. S2CID   31244527.
  6. Stott, Rebecca. "Darwin's ghosts: the secret history of evolution" New York, Spiegel & Grau (2012). ISBN   9781400069378
  7. "NOAA's Coral Reef Conservation Program: New Analysis: 75% of Coral Reefs Under Threat". coralreef.noaa.gov. Retrieved 2015-06-08.
  8. Burke, Reytar (2011). "Reefs at Risk Revisited". World Resources Institute.Cite journal requires |journal= (help)
  9. Barrero-Canosa-1, Duenas-2, Sanchez-3, J.-1, L.F.-2, J.A.-3 (March 2013). "Isolation of potential fungal pathogens in gorgonian corals at the Tropical Eastern Pacific". Coral Reefs; Heidelberg. 32 (1): 35–41. Bibcode:2013CorRe..32...35B. doi:10.1007/s00338-012-0972-2. S2CID   17561903. ProQuest   1357199805.CS1 maint: multiple names: authors list (link)
  10. Markey, Kathryn L., Baird, Andrew H., Humphrey, Craig, and Negri, Andrew P (2007). "Insecticides and a fungicide affect multiple coral life stages" (PDF). Marine Ecology Progress Series. 330: 127–137. Bibcode:2007MEPS..330..127M. doi: 10.3354/meps330127 .CS1 maint: multiple names: authors list (link)
  11. Yuyama, Ikuko; Ito, Yoshihiko; Watanabe, Toshiki; Hidaka, Michio; Suzuki, Yoshimi; Nishida, Mutsumi (2012). "Differential gene expression in juvenile polyps of the coral Acropora tenuis exposed to thermal and chemical stresses". Journal of Experimental Marine Biology and Ecology. 430–431: 17–24. doi:10.1016/j.jembe.2012.06.020.

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Cnidaria Aquatic animal phylum having cnydocytes

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Coral Marine invertebrates of the class Anthozoa

Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.

Hydrozoa class of cnidarians

Hydrozoa are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most living in salt water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in fresh water. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria.

<i>Obelia</i> Genus of hydrozoans

Obelia is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic organisms that are relatively simple in structure.

Anthozoa Class of cnidarians without a medusa stage

Anthozoa is a class of marine invertebrates which includes the sea anemones, stony corals and soft corals. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as part of the plankton. The basic unit of the adult is the polyp; this consists of a cylindrical column topped by a disc with a central mouth surrounded by tentacles. Sea anemones are mostly solitary, but the majority of corals are colonial, being formed by the budding of new polyps from an original, founding individual. Colonies are strengthened by calcium carbonate and other materials and take various massive, plate-like, bushy or leafy forms.

Scleractinia Order of Hexacorallia which produce a massive stony skeleton

Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. 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 in colonial species the polyps are usually only a few millimetres in diameter. These polyps reproduce asexually by budding, but remain attached to each other, forming a multi-polyp colony of clones with a common skeleton, which may be up to several metres in diameter or height according to species.

Medusozoa Clade of marine invertebrates

Medusozoa is a clade in the phylum Cnidaria, and is often considered a subphylum. It includes the classes Hydrozoa, Scyphozoa, Staurozoa and Cubozoa, and possibly the parasitic Polypodiozoa. Medusozoans are distinguished by having a medusa stage in their often complex life cycle, a medusa typically being an umbrella-shaped body with stinging tentacles around the edge. With the exception of some Hydrozoa, all are called jellyfish in their free-swimming medusa phase.

<i>Carybdea</i> Genus of jellyfishes

Carybdea is a genus of venomous box jellyfish within the family Carybdeidae that currently consists of a total of 8 species. This genus of jellyfish are often found in warm waters around the world in waters such as the Mediterranean Sea, the Pacific Ocean, and off the coast of Africa. Their sting can cause a range of effects depending on the species. These invertebrates will go through both sexual and asexual reproduction as they transform from a polyp to medusa. Carybdea have a box-shaped bell with four tentacles and eye-like sensory structures. There are distinct physical markings that differentiate many species within the genus. While Carybdea use their venom to act as predators, they are also preyed on by turtles and various fish. They feed on plankton, invertebrates, fish, and some crustaceans.

<i>Turritopsis dohrnii</i> Species of small, biologically immortal jellyfish

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<i>Aiptasia</i> Genus of sea anemones

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<i>Carukia barnesi</i> Species of jellyfish

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Sea anemone Marine animals of the order Actiniaria

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<i>Condylactis gigantea</i> Species of sea anemone

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<i>Eusmilia</i> Genus of corals

Eusmilia is a genus of stony coral in the family Meandrinidae. It is a monotypic genus represented by the species Eusmilia fastigiata, commonly known as the smooth flower coral. It is found on reefs in the Caribbean Sea.

Mesentery (zoology) Membrane inside the body cavity of an animal

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Cycloseris curvata is a species of disc coral in the family Fungiidae. Cyclosteris curvata is a mostly solitary free living scleractinian disc coral found in the indo-pacific region. They grow on soft substrates and are known to tolerate turbid waters. Like other anthozoan corals they lack a medusa stage characteristic of other cnidarians. They have been observed as both green and brown in color in the field.

<i>Clytia hemisphaerica</i> Species of hydrozoan

Clytia hemisphaerica is a small hydrozoan-group cnidarian, about 1 cm in diameter, that is found in the Mediterranean Sea and the North-East Atlantic Ocean. Clytia has the free-swimming jellyfish form typical of the Hydrozoa, as well as vegetatively propagating polyps.

<i>Clava</i> (hydrozoa) Genus of hydrozoans

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