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Cnidaria
Fossil range: Ediacaran - Recent
Sea nettles, Chrysaora quinquecirrha
Sea nettles, Chrysaora quinquecirrha
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Cnidaria
Hatschek, 1888
Subphylum/Classes[2]
Anthozoa — corals and sea anemones
Medusozoa:[1]
Cubozoa — sea wasps or box jellyfish
Hydrozoa — hydroids, hydra-like animals
Polypodiozoa
Scyphozoa — jellyfish
Staurozoa — stalked jellyfish
Unranked:
Myxozoa - parasites

Cnidaria[3] (pronounced /naɪˈdɛəriə/[4]) is a phylum containing some 9,000 species [5] of animals found exclusively in aquatic, mostly marine, environments. The Ediacaran Period (ˌiːdiˈækərən named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic The stinging sea nettle ( Chrysaora quinquecirrha) is a Species of Jellyfish occurring particularly in Atlantic estuaries Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Anthozoa is a class within the phylum Cnidaria that contains the Sea anemones and Corals Unlike other cnidarians anthozoans do not have a medusa 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 Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments Box jellyfish are invertebrates belonging to the class Cubozoa, named for their Cube -shaped medusae. Hydrozoa ( hydrozoans) are a Taxonomic class of very massive predatory animals which can be solitary or colonial and which mostly live in saltwater Hydroid may refer to Marine Biology Colonial plant-like animals closely related to jellyfish with stinging cells any member of the invertebrate order Hydroida (class Hydra is a Genus of simple fresh-water animals possessing radial symmetry. Polypodium is a Monotypic Genus of strange parasitic animals the only genus in family Polypodiidae. Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the Stauromedusae, or the stalked jellyfishes, is an order of Jellyfish within the Cnidaria phylum that are unique in that they do not enter The Myxozoa ( Etymology: Greek: myx- "slime" or "mucus" + zoa "animals" are a group of parasitic Parasitism is a type of symbiotic relationship between Organisms of different Species. A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. Despite their early appearance in the evolutionary history of animals and their simple morphology, the modern forms are genetically sophisticated and bio-chemically complex.

The unifying characteristic of the Cnidarians is the presence of cnidocytes, specialized cells that carry organelles called nematocysts. A cnidocyte, cnidoblast or nematocyte, is a type of Venomous cell unique to the Phylum Cnidaria ( Corals In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed It is widely accepted that all cnidarians inherited cnidocytes from a single common ancestor. [6] As for the etymology, the word Cnidaria comes from the Greek word "cnidos", which means "stinging nettle". Urtica dioica, commonly called stinging nettle, is a Herbaceous perennial Flowering plant, native to Europe, Asia, The corals, which are important reef-builders are placed in this phylum, along with sea anemones, jellyfish, sea pens, sea pansies and sea wasps. Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many 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 Sea anemones are a group of water dwelling predatory animals of the order Actiniaria; they are named after the Anemone, a terrestrial Flower Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the Sea pens are colonial marine Cnidarians belonging to the order Pennatulacea. Sea pens are colonial marine Cnidarians belonging to the order Pennatulacea. Box jellyfish are invertebrates belonging to the class Cubozoa, named for their Cube -shaped medusae. The name Coelenterata was formerly applied to the group, but as this name included the Ctenophores, it has been abandoned. Coelenterata is an obsolete long term encompassing two animal phyla, the Ctenophora (comb jellies and the Cnidaria ( Coral animals true The phylum Ctenophora (tɨˈnɒfərə commonly known as comb jellies, is a phylum that includes the Sea gooseberry ( Pleurobrachia pileus) and Cnidarians are highly evident in the fossil records, having first appeared in the Ediacaran period. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. The Ediacaran Period (ˌiːdiˈækərən named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic

The basic body shape of a cnidarian consists of a sac containing a gastrovascular cavity with a single opening that functions as both mouth and anus. Gastro vascular cavity, as the name indicates functions in both Digestion and Gas exchange. 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 The anus is an opening at the opposite end of an Animal 's Digestive tract from the Mouth. It has radial symmetry, meaning that whichever way it is cut along its central axis, the resulting halves would always be mirror images of each other. "Bilateral symmetry" redirects here For bilateral symmetry in mathematics see Reflection symmetry. Their movement is coordinated by a decentralized nerve net and simple receptors. A nerve is an enclosed cable-like bundle of peripheral Axons (the long slender projections of Neurons. Several free-swimming Cubozoa and Scyphozoa possess rhopalia, complex sensory structures that can include image-forming eyes with lenses and retinas [7] and a gravity-sensing statolith comparable in function to the otolith of the vertebrate inner ear. Rhopalia (singular rhopalium) are small sensory structures of scyphozoan and Cubozoan Jellyfish; in Aurelia they lie in marginal Statoliths are a specialized form of Amyloplasts involved in Gravity perception by Plants These specialized amyloplasts are denser than the Cytoplasm An otolith, (οτο- oto-, ear + λιθος lithos, a stone also called statoconium or otoconium is a structure in the Saccule Tentacles surrounding the mouth contain nematocysts, specialized stinging cells, which they use to catch prey and defend themselves from predators. The ability to sting is what gives cnidarians their name. A stinger (a Colloquialism for the term "sting" is a common term for a sharp organ or body part found in various Animals (typically Arthropods

There are four main classes of Cnidaria:

Traditionally the hydrozoans were considered to be the most primitive, but evidence now suggests the anthozoans were actually the earliest to diverge. Sea anemones, sea fans and corals are in this class. The non-anthozoan classes may be grouped into the subphylum Medusozoa. Under this scheme, Anthozoa is also elevated to a subphylum. [2]

Theoretically, members of Cnidaria have life-cycles that alternate between asexual polyps and sexual, free-swimming forms called medusae. In Zoology, a polyp is one of two forms of individuals found in many species of Cnidarians 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 In reality there is a vast variation within the life-cycles of cnidarians.

Contents

Nutrition

Most cnidaria feed on prey that come into contact with their tentacles. These include the larger of the protists, various worms, crabs, other cnidaria and even fish. Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this A worm is a common name given to a diverse group of invertebrate animals that have a long soft body and no legs Crabs are decapod Crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (βραχύ / brachy Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Some groups such as coral live symbiotically with algae, mostly Dinoflagellata but sometimes Chlorophyta. Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek The dinoflagellates are a large group of Flagellate Protists Most are marine Plankton, but Chlorophyta, a division of Green algae, of mostly aquatic Photosynthetic Eukaryotic organisms By absorbing the methane produced by the sea pansy, utilizing sunlight via photosynthesis and releasing the oxygen, the algae produce energy-rich carbohydrates which the cnidarian uses as its main source of food. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most

Development of a cnidarian
Development of a cnidarian

Reproduction

Cnidarians reproduce both sexually and asexually. They reproduce asexually by budding. The bud will eventually fall off the parent organism and becomes a new polyp. Some cnidarians reproduce sexually by releasing egg and sperm into the water. The eggs will be fertilized by sperm and develop into a larva called planula. The planula will then develop into a new polyp which will produce new medusa called ephyra. Medusa body types of cnidarians have both sexual and asexual stages. The stages alternate. Medusa reproduce sexually to produce polyps, which will grow up and reproduce new medusa.

Cnidaria as fossils

The phylum has existed for a long time, having arguably been among the Ediacaran or Vendian biota of the later Proterozoic eon, about 580 to 540 million years ago, and cnidaria were among the first recognised animal fossils. The Ediacara (ˌiːdɪˈækərə formerly Vendian) biota are ancient lifeforms of the Ediacaran Period which represent the earliest known complex The Proterozoic (ˌproʊtərəˈzoʊɪk is a geological eon representing a period before the first abundant complex life on Earth. Our understanding of fossil groups is varied; while those cnidaria that were formed of soft tissue only remain today in very exceptional cases, the fossil record of, for example, corals is very well known due to the lime remains they left behind. The first coral reefs date from the early Ordovician of about 500 million years ago, and their form at the time differed significantly from that of corals today, which, following the mass extinction 240 million years ago at the end of the Permian period, first appeared in the middle of the Triassic period. The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period The Permian is a geologic period and system that extends from 299 The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago

Classification

In the past, Cnidaria were classically grouped together with ctenophora as Coelenterata. The phylum Ctenophora (tɨˈnɒfərə commonly known as comb jellies, is a phylum that includes the Sea gooseberry ( Pleurobrachia pileus) and Coelenterata is an obsolete long term encompassing two animal phyla, the Ctenophora (comb jellies and the Cnidaria ( Coral animals true In view of current research into cladistics, this group is now considered paraphyletic, i. Cladistics is the hierarchical classification of Species based on evolutionary ancestry e. it does not include all the descendants of their common ancestor. Despite the outer similarity of the two taxa, such as their radially symmetric bodies, the ctenophora are more likely to be related to the mirror-symmetrical bilateria than cnidaria. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to The Bilateria (ˌbaɪləˈtɪəriə are all animals having a bilateral symmetry, i For this reason Coelenterata is considered to be an artificial grouping from a cladistic viewpoint.

Cnidaria are further divided into six main classes:

Among the hydrozoa the order of Siphonophora, which includes the Portuguese Man o' War, deserves special mention. The Portuguese Man O' War ( Physalia physalis) also known as the blue bubble, blue bottle, man-of-war, or the Portuguese man of war These hydrozoans form colonies that show varying degrees of specialization, so that in extreme cases individuals function essentially as organs of the whole.

A small group of microscopic parasites, the Myxozoa, have been considered to be extremely reduced cnidarians. Parasitism is a type of symbiotic relationship between Organisms of different Species. The Myxozoa ( Etymology: Greek: myx- "slime" or "mucus" + zoa "animals" are a group of parasitic These attach themselves to their hosts by polar filaments similar to the stinging threads of cnidocysts. Their exact placement within the phylum is uncertain, however, and new studies suggest they may have developed from some other group of animals. Usually they are placed in their own phylum.

Finally, the classification of the extinct Conularids is still a matter of contention among taxonomist. The Conulariida are a poorly understood extinct phylum Some doubt exists about whether they should even be assigned to the Animalia Structure The conulariids Some experts question whether this group should even be included in the animal kingdom.

Obsolete names for groups of cnidarians include Acalephae, which contained Hydrozoa and Scyphozoa, based on the shared character of stinging cells; however this character is no longer thought to be primitive.

Cnidaria and man

A large number of the islands humans inhabit today can be traced back to the carcasses of dead cnidaria. The limestone they left behind is often extracted and commercially exploited, particularly in the manufacture of cement. In the most general sense of the word a cement is a binder a substance which sets and hardens independently and can bind other materials together Jewelry has been made from particularly colourful coral since prehistoric times.

Some species of cnidaria are edible and are often used in Eastern Asian cuisine. Cuisine (from French cuisine, "cooking culinary art kitchen" ultimately from Latin coquere, "to cook" is a specific set

On the other hand, humans are regularly killed or permanently disabled by the cnidarian's highly poisonous neurotoxin, particularly on the north coast of the Australian continent. The North Sea is also inhabited by cnidaria that can cause acutely painful skin wounds.

Conversely, the spread of human tourism often has a negative effect on coral. The global death of coral shows that in reef biology corals are a key organism, whose death often precedes the extinction of the entire ecosystem. The introduction of nitrate-heavy effluent and cyanide fishing are only some of the human influences that in a short space of time can cause the destruction of wide-ranging habitats. Cyanide fishing is an illegal form of Fishing (commonly known as Poaching) common in South East Asia, which usually uses the Chemical compound Another danger for coral is the rising water temperatures caused by climate change: if they rise too high, the corals lose the algae with which they live in symbiosis and perish.

Notes and references

Notes

  1. ^ Classes in Medusozoa based on The Taxonomicon - Taxon: Subphylum Medusozoa - Retrieved July 10, 2007
  2. ^ a b Subphyla Anthozoa and Medusozoa based on The Taxonomicon - Taxon: Phylum Cnidaria - Retrieved July 10, 2007
  3. ^ This article is partially based on a translation of the corresponding Roman-language Wikipedia article, retrieved on 27 April 2006. Events 48 BC - Battle of Dyrrhachium, Julius Caesar barely avoids a catastrophic defeat to Pompey in Macedonia. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 48 BC - Battle of Dyrrhachium, Julius Caesar barely avoids a catastrophic defeat to Pompey in Macedonia. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  4. ^ Silent c - from New Latin cnida, from Greek κνιδη "nettle", "sea anemone" (Dalby, 2003: 296). In an alphabetic writing system, a silent letter is a letter that in a particular word does not correspond to any sound in the word's Pronunciation. The term New Latin or Neo-Latin is used to describe a form the Latin language used between the end of the Medieval Latin period (c Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Nettle is the common name for between 30-45 species of Flowering plants of the genus Urtica in the family Urticaceae, with a cosmopolitan though Sea anemones are a group of water dwelling predatory animals of the order Actiniaria; they are named after the Anemone, a terrestrial Flower
  5. ^ Harrison I, Laverty H, Sterling E (2004). Species Diversity. Connexions. Rice University. Retrieved on 2008-05-23. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne
  6. ^ Caldwell, Roy (2008). Introduction to Cnidaria. Museum of Paleontology - University of California. University of California - Berkley. Retrieved on 2008-05-23. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne
  7. ^ Caldwell, Roy (2008). Cubozoa: More on Morphology. Museum of Paleontology - University of California. University of California - Berkley. Retrieved on 2008-05-23. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne

References

Journal articles

External links

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