NationMaster - Encyclopedia: Flatworm

The flatworms (Phylum Platyhelminthes from the Greek platy, meaning "flat" and helminth, meaning worm) are a phylum of relatively simple soft-bodied invertebrate animals. With about 25,000 known species^[1] they are the largest phylum of acoelomates. Flatworms are found in marine, freshwater, and even damp terrestrial environments. A troublesome terrestrial example is the New Zealand flatworm, Arthurdendyus triangulatus, which rapidly colonized large areas of Ireland and Scotland since its unintentional introduction in the 1960s and has since destroyed most of the indigenous earthworms^[2] . Most flatworms are free-living, but many are parasitic. There are four classes: Trematoda (flukes), Cestoda (tapeworms), Monogenea, and Turbellaria. Image File history File links Wikispecies-logo. ... Wikispecies is a wiki-based online project supported by the Wikimedia Foundation that aims to create a comprehensive free content catalogue of all species (including animalia, plantae, fungi, bacteria, archaea, and protista). ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... For other uses, see Animal (disambiguation). ... For other uses, see Species (disambiguation). ... Picture of Human body cavities - dorsal body cavity to the left and ventral body cavity to the right. ... Binomial name Arthurdendyus triangulatus (Dendy, 1894) Synonyms Artioposthia triangulata The New Zealand flatworm (Arthurdendyus triangulatus) is a large flatworm native to New Zealand. ... A parasite is an organism that lives in or on the living tissue of a host organism at the expense of it. ... A class is the rank in the scientific classification of organisms in biology below Phylum and above Order. ... Subclasses Aspidogastrea Digenea The Trematoda is a class within the phylum Platyhelminthes, which contains two groups of parasitic worms. ... This article contains material from the CDC (Center for Disease Control) website which, as a US government publication, is in the public domain. ... Monogenea (adj. ... Orders Acoela Catenulida Haplopharyngida Lecithoepitheliata Macrostomida Nemertodermata Polycladida Prolecithophora Rhabdocoela Seriata Turbellaria are a group of generally small (<1 - 60cm) and free-swimming members of the flatworm phylum Platyhelminthes. ...

Description

The flatworm’s cephalized soft body is ribbon-shaped, flattened dorso-ventrally (from top to bottom), and bilaterally symmetric. Flatworms are the simplest triploblastic animals with organs. This means their organ systems form out of three germ layers: an outer ectoderm and an inner endoderm with a mesoderm between them. Turbellarians generally have a ciliated epidermis. There is also no true body cavity (coelom) except the gut; hence, flatworms are classified as acoelomates. The interior of the acoelomate body is filled with somewhat loosely spaced mesodermal tissue called parenchyma tissue. This article or section does not cite any references or sources. ... Illustration of the different types of symmetry of Life Forms On Earth. ... Triploblasty is a condition of the ovum in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm. ... This article is about the biological unit. ... Organs derived from each germ layer. ... The ectoderm is outermost of the three germ layers of the developing embryo, the other two being the mesoderm and the endoderm. ... Endoderm is one of the germ layers formed during animal embryogenesis. ... The mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ... Squamous epithelium is one of several types of epithelia. ... Picture of Human body cavities - dorsal body cavity to the left and ventral body cavity to the right. ... Parenchyma is a term used to describe a bulk of a substance. ...

Depending on species and age, individuals can range in size from almost microscopic to over 20 m long. The longest ever recorded flatworm was a tapeworm over 90 ft (27 m) long.^[3] This article is about the unit of length. ... Orders Subclass Cestodaria Amphilinidea Gyrocotylidea Subclass Eucestoda Aporidea Caryophyllidea Cyclophyllidea Diphyllidea Lecanicephalidea Litobothridea Nippotaeniidea Proteocephalidea Pseudophyllidea Spathebothriidea Tetraphyllidea Trypanorhyncha In biology, Cestoda is the class of parasitic flatworms, called cestodes or tapeworms, that live in the digestive tract of vertebrates as adults and often in the bodies of various animals... A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, â€² â€“ a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ...

Haptor

The haptor is a part of Platyhelminthes used to attach to its host. These differ between the prohaptor which is on the anterior end of the body and the opisthaptor, which is part of the posterior end of the body.

The prohaptor has various adhesive and feeding structures. In some species, the prohaptor may have a number of cephalic or head glands that secrete a sticky adhesive substance, and shallow muscular suckers, all used for attachment. In other species there is an oral sucker, with various degrees of muscularisation that surrounds the mouth.

The opisthaptor is primarily responsible for the attachment of the monogeneans to the host. The morphology of the opisthaptor is highly variable. It may have suckers in various degrees of development, large hooks called anchors (or hamuli), small hooks that are remnants from the larval stage, or complex clamps that may be either muscular or sclerotised.

Circulation and nervous system

There is no true circulatory or respiratory system, but like all other animals, flatworms do take in oxygen. Extracellular body fluids (interstitial fluids) percolate between cells to help distribute nutrients, gases, and waste products. For transport in plants, see Vascular tissue. ... Among quadrupeds, the respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. ... The word Animals when used alone has several possible meanings in the English language. ... Interstitial fluid (or tissue fluid, or intercellular fluid) is a solution which bathes and surrounds the cells of multicellular animals. ... A nutrient is a substance used in an organisms metabolism which must be taken in from the environment. ... For other uses, see Gas (disambiguation). ...

Flatworms respire at their integument; gasses diffuse directly across their moist outer surface. This type of system is called integumentary exchange. In animal physiology, respiration is the transport of oxygen from the ambient air to the tissue cells and the transport of carbon dioxide in the opposite direction. ... In zootomy, the integumentary system is the external covering of the body, comprising the skin, hair, scales, nails, sweat glands and their products (sweat and mucus). ...

However, flatworms do have a bilateral nervous system; they are the simplest animals to have one. Two cordlike nerves branch repeatedly in an array resembling a ladder. The head end of some species even has a collection of ganglia acting as a rudimentary brain to integrate signals from sensory organs such as eyespots. The nervous system is a highly specialized network whose principal components are nerves called neurons. ... This is a dorsal root ganglion (DRG) from a chicken embryo (around stage of day 7) after incubation overnight in NGF growth medium stained with anti-neurofilament antibody. ... The human eye is the first element of a sensory system: in this case, vision, for the visual system. ...

Feeding

Usually the digestive tract has one opening, so the animal can't feed, digest, and eliminate undigested particles of food simultaneously, as most animals with tubular guts are able to do. This blind-ended gastrovascular cavity functions similarly to that of the Cnidaria. However, in a few particularly long flatworms or those with highly branched guts, there may be one or more anuses. A small group where the gut is absent or non-permanent, called acoel flatworms, appear to be unrelated to the other Platyhelminthes (see below). Gut redirects here. ... Gastrovascular cavity, as the name indicates, functions in both digestion and the transport of nutrients to all parts of an animal body. ... Subphylum/Classes[2] Anthozoa â€” corals and sea anemones Medusozoa:[1] Cubozoa â€” sea wasps or box jellyfish Hydrozoa â€” hydroids, hydra-like animals Polypodiozoa Scyphozoa â€” jellyfish Staurozoa â€” stalked jellyfish Unranked: Myxozoa - parasites Cnidaria[3] (pronounced [4]) is a phylum containing some 11,000 species of apparently simple animals found exclusively in aquatic... This article is about the bodily orifice. ...

Despite the simplicity of the digestive chamber, they are significantly more complex than cnidarians in that they possess numerous organs, and are therefore said to show an organ level of organization. Mesoderm allows for the development of these organs, and true muscle. Major sense organs are concentrated in the front end of the animals for species who possess these organs. Classes Anthozoa - Corals and sea anemones Cubozoa - Sea wasps or box jellyfish Hydrozoa - Hydroids, hydra-like animals Scyphozoa - Jellyfish Cnidaria is a phylum containing some 10,000 species of relatively simple animals found exclusively in aquatic environments (most species are marine). ... This article is about the biological unit. ... For other uses of Muscles, see Muscles (disambiguation). ...

Muscular contraction in the gut causes a strong sucking force which allows flatworms to ingest food. For other uses of Muscles, see Muscles (disambiguation). ...

Reproduction

Flatworm reproduction is hermaphroditic, meaning each individual produces eggs and sperm. When two flatworms mate, they exchange sperm so both become fertilized. Some flatworms, such as Pseudobiceros hancockanus engage in penis fencing, in which two individuals fight, trying to pierce the skin of the other with their penises; the first to succeed inseminates the other, which must then carry and nourish the fertilized eggs.^[4] Flatworms usually do not fertilize their own eggs. For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ... For other uses, see Hermaphrodite (disambiguation). ... A human ovum Sperm cells attempting to fertilize an ovum An ovum (plural ova) is a haploid female reproductive cell or gamete. ... A spermatozoon or spermatozoan ( spermatozoa), from the ancient Greek ÏƒÏ€ÎÏÎ¼Î± (seed) and (living being) and more commonly known as a sperm cell, is the haploid cell that is the male gamete. ... Two flatworms (of the species Pseudobiceros hancockanus) penis fencing. ...

Turbellarians classified as planarians (usually freshwater, non-parasitic) can also reproduce asexually by transverse fission. The body constricts at the midsection, and the posterior end grips a substrate. After a few hours of tugging, the body rips apart at the constriction. Each half grows replacements of the missing pieces to form two whole flatworms. This also means that if one of these planarian flatworms is cut in half, each half will regenerate, forming two separate, fully-functioning flatworms. Planariam (family Planariidae) are common freshwater, non-parasitic flatworms of the phylum Platyhelminthes, class Turbellaria. ... This article is about human asexuality; asexual reproduction is a separate topic. ...

Classes

Flatworms were formerly considered to be basal among the protostomes. Molecular evidence suggests that this is only true of the orders Acoela and Nemertodermatida, which are thus given their own phylum Acoelomorpha. These findings, however, are still not accepted by all biologists. The systematic position of Catenulida seems uncertain, although Donoghue and Cracraft would place it as a sister group to all other non-Acoelomorpha flatworms.^[5] Xenoturbella was at first believed to be a flatworm as well, but it is now obvious that it belongs in its own phyla. The remaining and true flatworms form a monophyletic group that developed from more complex ancestors, and grouped with several other phyla as the Platyzoa. The traditional classifications of flatworms is primarily based on differing degrees of parasitism and divided into three monophyletic classes: Image File history File links Download high resolution version (2300x3271, 1790 KB) Summary The 75th plate from Ernst Haeckels Kunstformen der Natur (1904), depicting organisms classified as Platodes. ... Image File history File links Download high resolution version (2300x3271, 1790 KB) Summary The 75th plate from Ernst Haeckels Kunstformen der Natur (1904), depicting organisms classified as Platodes. ... Ernst Haeckel. ... The 8th print, Discomedusae. ... Groups Ecdysozoa Lophotrochozoa Platyzoa Protostomes (from the Greek: first the mouth) are a taxon of animals. ... Families Actinoposthiidae Anaperidae Antigonariidae Antroposthiidae Childiidae Convolutidae Dakuidae Diopisthoporidae Hallangiidae Haploposthiidae Hofsteniidae Isodiametridae Mecynostomidae Nadinidae Otocelididae Paratomellidae Polycanthiidae Proporidae Sagittiferidae Solenofilomorphidae Taurididae Acoela is an order of animals treated either as a group of flatworms or as one of the two classes of the phylum Acoelomorpha, containing the majority of... The Acoelomorpha are a phylum of animals formerly considered flatworms, but now known to be a separate group, basal among the Bilateria. ... Xenoturbella is a genus of Bilaterian animals; it is a marine worm. ... The Platyzoa are a group of protostome animals. ...

The remaining flatworms are grouped together for convenience as the class Turbellaria, now comprising the following orders: Subclasses Aspidogastrea Digenea The Trematoda is a class within the phylum Platyhelminthes, which contains two groups of parasitic worms. ... This article contains material from the CDC (Center for Disease Control) website which, as a US government publication, is in the public domain. ... Monogenea (adj. ... A life cycle is a period involving one generation of an organism through means of reproduction, whether through asexual reproduction or sexual reproduction. ... Orders Acoela Catenulida Haplopharyngida Lecithoepitheliata Macrostomida Nemertodermata Polycladida Prolecithophora Rhabdocoela Seriata Turbellaria are a group of generally small (<1 - 60cm) and free-swimming members of the flatworm phylum Platyhelminthes. ...

Most of these groups include free-living forms. The flukes and tapeworms, though, are parasitic, and a few cause massive damage to humans and other animals. The Candy-Cane Worm (Plagiostomum vittatum), a common North-East Atlantic species. ... Families Bdellouridae Bipaliidae Dendrocoelidae Dugesiidae Geoplanidae Kenkiidae Nexilidae Planariidae Procerodidae Rhynchodemidae Uteriporidae Tricladida (Triclads) [1] is an order of the Archoophora subclass. ... The Polycladida represents a highly diverse clade of free-living marine turbellarian flatworms. ... This article is about modern humans. ...

Biochemical memory experiments

In 1955, Thompson and James V. McConnell conditioned planarian flatworms by pairing a bright light with an electric shock. After repeating this several times they took away the electric shock, and only exposed them to the bright light. The flatworms would react to the bright light as if they had been shocked. Thompson and McConnell found that if they cut the worm in two, and allowed both worms to regenerate each half would develop the light-shock reaction. In 1962, McConnell repeated the experiment, but instead of cutting the trained flatworms in two he ground them into small pieces and fed them to other flatworms. Incredibly these flatworms learned to associate the bright light with a shock much faster than flatworms who had not been fed trained worms. James V. McConnell (October 26, 1925-April 9, 1990) was an American biologist and animal psychologist. ...

This experiment intended to show that memory could perhaps be transferred chemically. The experiment was repeated with mice, fish, and rats, but it always failed to produce the same results, . The perceived explanation was that rather than memory being transferred to the other animals, it was the hormones in the ingested ground animals that changed its behaviour.^[6] McConnell believed that this was evidence of a chemical basis for memory, which he identified as memory RNA. McConnell's results are now attributed to observer bias.^[7] No double-blind experiment has ever reproduced his results.

References

^ Species Register. Flatworms - Phylum Platyhelminthes. Marine Discovery Centres. Retrieved on 2007-04-09.
^ Boag, B, K A Evans, G W Yeates, P M Johns & R Nielson (1995). "Assessment of the global potential distribution of the predatory land planarian Artioposthia triangulata (Dendy) (Tricladida: Terricola) from ecoclimatic data". New Zealand Journal of Zoology 22: 311–318.
^ Phylum Platyhelminthes. PBS.
^ Leslie Newman. Fighting to mate: flatworm penis fencing. PBS.
^ Donoghue, Michael J. and Joel Cracraft. (2004): Assembling the Tree of Life. Oxford University Press. ISBN 0195172345 P. 213. On-line at Google Books
^ Bob Kentridge. Investigations of the cellular bases of memory. University of Durham. Retrieved on 2007-02-08.
^ Rilling, M. (1996). "The mystery of the vanished citations: James McConnell's forgotten 1960s quest for planarian learning, a biochemical engram, and celebrity.". American Psychologist 51: 589-598. Retrieved on 2007-5-23.

Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 99th day of the year (100th in leap years) in the Gregorian calendar. ... PBS redirects here. ... PBS redirects here. ... Durham University is a university in England. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 39th day of the year in the Gregorian calendar. ...

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