Anatomy of a coral polyp.

In zoology, a polyp is one of two forms of individuals found in many species of cnidarians. Zoology (from Greek ζῷον, zoon, "animal" + λόγος, " Logos " "knowledge" is the branch of Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments The two are the polyp or hydroid and the medusa. In Biology, a medusa (plural medusae is a form of Cnidarian in which the body is shortened on its principal axis and broadened sometimes greatly in contrast Polyps are approximately cylindrical, elongated on the axis of the body. A cylinder is one of the most basic curvilinear geometric shapes the Surface formed by the points at a fixed distance from a given Straight line, the axis The aboral end is attached either to the substrate by means of a disc-like holdfast if the polyp is solitary, or is connected to other polyps, either directly or indirectly, if the polyp is part of a colony. In Biology, aboral surfaces are surfaces away from or opposite the mouth In Biology a substrate is the surface a plant or animal lives upon A holdfast is a Root -like structure that anchors aquatic Sessile organisms such as Seaweed, other sessile Algae, stalked In Biology, a colony (from Latin colonia) refers to several individual Organisms of the same Species living closely together usually The oral end bears the mouth, and is surrounded by a circlet of tentacles. The mouth, buccal cavity, or oral cavity is the first portion of the Alimentary canal that receives food and begins digestion by mechanically breaking up Tentacles can refer to the elongated flexible organs that are present in some animals especially Invertebrates and sometimes to the hairs of the leaves of some insectivorous

Classes

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. A class is the Taxonomic rank in the Biological classification of organisms in Biology below phylum and above order. Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many Sea anemones are a group of water dwelling predatory animals of the order Actiniaria; they are named after the Anemone, a terrestrial Flower Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many Hydrozoa ( hydrozoans) are a Taxonomic class of very massive predatory animals which can be solitary or colonial and which mostly live in saltwater A life cycle is a period involving 1 Generation of an Organism through means of Reproduction, whether through Asexual reproduction or Sexual In class Scyphozoa, the medusa stage is dominant, and the polyp stage may or may not be present, depending on the family. Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the In Biological classification, family ( Latin 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. A larva ( Latin; plural larvae) is a juvenile form of Animal with indirect development, undergoing Metamorphosis (for example A planula is the free-swimming flattened ciliated, bilaterally symmetric Larva of a Jellyfish, a Hydrozoan Cnidarian or Metamorphosis is a Biological process by which an Animal physically develops after Birth or hatching involving a conspicuous and relatively Strobilation or transverse fission is a form of Asexual reproduction consisting of the spontaneous transverse Segmentation of the body Once strobilation is complete, the polyp may die, or regenerate itself to repeat the process again later.

Anatomy

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 cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called The outer layer is known technically as the ectoderm, the inner layer as the endoderm (or gastroderm). A germ layer is a collection of cells formed during animal Embryogenesis. A germ layer is a collection of cells formed during animal Embryogenesis. Between ectoderm and endoderm is a supporting layer of structureless gelatinous substance termed mesogloea, secreted by the cell layers of the body wall. Mesoglea, also known as ectoplasma, is the clear inert jellylike substance that makes up most of the bodies of Jellyfish, Comb jellies and certain primitive 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. An endoskeleton is an internal support structure of an Animal. Cell migration is a central process in the development and maintenance of Multicellular organisms Tissue formation during embryonic development, Wound healing

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. Tentacles can refer to the elongated flexible organs that are present in some animals especially Invertebrates and sometimes to the hairs of the leaves of some insectivorous The tentacles are organs which serve both for the tactile sense and for the capture of food. In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument By means of the stinging nettle-cells or nematocysts with which the tentacles are thickly covered, living organisms of various kinds are firmly held and at the same time paralysed or killed, and by means of longitudinal muscular fibrils formed from the cells of the ectoderm the tentacles are contracted and convey the food to the mouth. A cnidocyte, cnidoblast or nematocyte, is a type of Venomous cell unique to the Phylum Cnidaria ( Corals By means of circularly disposed muscular fibrils formed from the endoderm the tentacles can be protracted or thrust out after contraction. By muscle fibres belonging to the same two systems, the whole body may be retracted or protruded.

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. The word peristome is derived from the Greek peri, meaning 'around' or 'about' and stoma, '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. Excretion is the process of eliminating waste products of Metabolism and other non-useful materials 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). Living fossil is an informal term for any living Species (or Clade) of organism which appears The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic 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. Hydrozoa ( hydrozoans) are a Taxonomic class of very massive predatory animals which can be solitary or colonial and which mostly live in saltwater Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many

In the class Hydrozoa, the polyps are indeed often very simple, like the common little freshwater species of the genus Hydra. Hydrozoa ( hydrozoans) are a Taxonomic class of very massive predatory animals which can be solitary or colonial and which mostly live in saltwater Freshwater is a word that refers to bodies of water such as Ponds lakes rivers and streams containing low concentrations of dissolved Salts and other Total dissolved In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic Hydra is a Genus of simple fresh-water animals possessing radial symmetry. 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. Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many Sea anemones are a group of water dwelling predatory animals of the order Actiniaria; they are named after the Anemone, a terrestrial Flower The stomodeum, also called stomatodeum, is a depression between the Brain and the Pericardium in an Embryo, and is the precursor of the In Anatomy, the mesentery is the double layer of Peritoneum that suspends the Jejunum and Ileum from the posterior wall of the Abdomen Many of the mesenteries project into the enteric cavity but some extend from the body wall to the central stomodaeum.

Reproduction

It is an almost universal attribute of polyps to possess the power of reproducing themselves asexually by the method of budding. Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization. Budding (also called burgeoning) is the formation of a new Organism by the protrusion of part of another organism 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. Reproduction is the Biological process by which new individual Organisms are produced The Evolution of sexual reproduction is a major puzzle The first Fossilized evidence of sexually reproducing Organisms is from Eukaryotes of the Stenian In Biology, offspring are the product of Reproduction, a new Organism produced by one or more Parents Collective offspring may be known A sex organ, or primary sexual characteristic, as narrowly defined is any of the anatomical parts of the body which are involved in sexual reproduction and constitute 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. In nautical terminology a reef is a rock, sandbar, or other feature lying beneath the surface of the water (six fathoms or less at low water

Etymology

The name polyp was given to these organisms from their supposed resemblance to an octopus (Fr. The poulpe), with its circle of writhing arms round the mouth. This comparison, though far-fetched, is certainly more reasonable than the common name "coral-insects" applied to the polyps which form coral.

References

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition article "Polyp", a publication now in the public domain. The Encyclopædia Britannica Eleventh Edition (1910–1911 is a 29-volume reference work that marked the beginning of the Encyclopædia Britannica The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone

See also

• Hydroids from Reunion Island and Indian Ocean
• Zoanthid
• Portuguese Man o' War