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Clava (cnidarian)
''Clava'' is a monotypic genus of hydrozoans in the family Hydractiniidae. It contains only one accepted species, ''Clava multicornis''. Other names synonymous with ''Clava multicornis'' include ''Clava cornea'', ''Clava diffusa'', ''Clava leptostyla'', ''Clava nodosa'', ''Clava parasitica'', ''Clava squamata'', ''Coryne squamata'', ''Hydra multicornis'', and ''Hydra squamata''. The larvae form of the species has a well developed nervous system compared to its small size. The adult form is also advanced due to its ability to stay dormant during unfavorable periods. Anatomy The larval form (planula) and adult form show two different body plans. The planula is a small, free-living larva, and is diploblastic with two layers: the endoderm and ectoderm with an additional mesoglea. The ectoderm thickness decreases from the anterior to posterior poles. Further, the ectoderm has mucous gland cells for secretory purposes, support, and sense along with cnidocytes with nematocysts in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
George Allman (natural Historian)
George James Allman FRS FRSE (181224 November 1898) was an Irish ecologist, botanist and zoologist who served as Emeritus Professor of Natural History at Edinburgh University in Scotland. Life Allman was born in Cork, Ireland, the son of James C. Allman of Bandon, and received his early education at the Royal Academical Institution, Belfast. For some time he studied for the Irish Bar, but ultimately gave up law in favour of natural science. In 1843, he graduated in medicine at Trinity College, Dublin, and in the following year was appointed professor of botany in that university, succeeding the botanist William Allman (1776–1846), who was the father of George Johnston Allman (distant relations of George). This position he held for about twelve years until he moved to Edinburgh as Regius Professor of natural history. There he remained until 1870, when considerations of health induced him to resign his professorship and retire to Dorset, where he devoted himself to his favo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalization
Cephalization is an evolutionary trend in which, over many generations, the mouth, sense organs, and nerve ganglia become concentrated at the front end of an animal, producing a head region. This is associated with movement and bilateral symmetry, such that the animal has a definite head end. This led to the formation of a highly sophisticated brain in three groups of animals, namely the arthropods, cephalopod molluscs, and vertebrates. Animals without bilateral symmetry Cnidaria, such as the radially symmetrical Hydrozoa, show some degree of cephalization. The Anthomedusae have a head end with their mouth, photoreceptive cells, and a concentration of neural cells. Bilateria Cephalization is a characteristic feature of the Bilateria, a large group containing the majority of animal phyla. These have the ability to move, using muscles, and a body plan with a front end that encounters stimuli first as the animal moves forwards, and accordingly has evolved to contain many of the b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phototropism
Phototropism is the growth of an organism in response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light contain a hormone called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the furthest side from the light. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism. Negative phototropism is not to be confused with skototropism which is defined as the growth towards darkness, whereas negative phototropism can refer to either the growth away from a light source or towards the darkness. Most plant shoots exhibit positive phototropism, and rearrange their chloroplasts in the leaves to maximize photosynthetic energy and promote growth.Goyal, A., Szarzyns ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chordate
A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These five synapomorphies include a notochord, dorsal hollow nerve cord, endostyle or thyroid, pharyngeal slits, and a post-anal tail. The name “chordate” comes from the first of these synapomorphies, the notochord, which plays a significant role in chordate structure and movement. Chordates are also Bilateral symmetry, bilaterally symmetric, have a coelom, possess a circulatory system, and exhibit Metameric, metameric segmentation. In addition to the morphological characteristics used to define chordates, analysis of genome sequences has identified two conserved signature indels (CSIs) in their proteins: cyclophilin-like protein and mitochondrial inner membrane protease ATP23, which are exclusively shared by all vertebrates, tunicates and cep ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phototaxis
Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis. Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite. Two types of positive phototaxis are observed in prokaryotes. The first is called scotophobotaxis (from the word " scotophobia"), which is observed only under a microscope. This occurs when a bacterium swims by chance out of the area illuminated by the microscope. Entering darkness signals the cell to reverse flagella rotation direction and reenter the light. The second type of phototaxis is true phototaxis, which is a directed movement up a gradient to an increasing amount of light. This is analogous to positive chemotaxis except that the attractant is light rather than a chem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tadpole
A tadpole is the larval stage in the biological life cycle of an amphibian. Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial. Tadpoles have some fish-like features that may not be found in adult amphibians such as a lateral line, gills and swimming tails. As they undergo metamorphosis, they start to develop functional lungs for breathing air, and the diet of tadpoles changes drastically. A few amphibians, such as some members of the frog family Brevicipitidae, undergo direct development i.e., they do not undergo a free-living larval stage as tadpoles instead emerging from eggs as fully formed "froglet" miniatures of the adult morphology. Some other species hatch into tadpoles underneath the skin of the female adult or are kept in a pouch until after metamorphosis. Having no hard skeletons, it might be expected that tadpole fossils would not exist. However, traces of biofilms have been preserved and fossil tadpoles have ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gonophore
A gonophore is a reproductive organ in Hydrozoa that produces gametes. It is a sporosac, a medusa or any intermediate stage. The name is derived from the Greek words (, that which produces seed) and (, -bearing). Gonophores are borne on branching stalks that grow out as a ring from the hydranth (i.e. the hydroid polyp, bearing a mouth, digestive cavity and tentacles) wall. The germ cells are formed from the inner layer of the entocodon. The entocodon is the primordium (i.e. the first cells that give rise to the development of an organ) of the subumbrella (i.e. the concave oral surface of a medusa) in the development of medusae from the gonophore. The gonophores in the order Leptomedusae are borne on much reduced hydranths and are usually protected in a peridermal (i.e. belonging to a hydroid perisarc) gonotheca. Medusae forming on fully developed hydranths are extremely rare; usually the gonophores develop into medusae or into sessile sporosacs. The gonophores in the superfam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinoic Acid
Retinoic acid (used simplified here for all-''trans''-retinoic acid) is a metabolite of vitamin A1 (all-''trans''-retinol) that mediates the functions of vitamin A1 required for growth and development. All-''trans''-retinoic acid is required in chordate animals, which includes all higher animals from fish to humans. During early embryonic development, all-''trans''-retinoic acid generated in a specific region of the embryo helps determine position along the embryonic anterior/posterior axis by serving as an intercellular signaling molecule that guides development of the posterior portion of the embryo. It acts through Hox genes, which ultimately control anterior/posterior patterning in early developmental stages. All-''trans''-retinoic acid (ATRA) is the major occurring retinoic acid, while isomers like 13-''cis''- and 9-''cis''-retinoic acid are also present in much lower levels. The key role of all-''trans''-retinoic acid in embryonic development mediates the high teratogenici ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Citral
Citral is an acyclic monoterpene aldehyde, and being a monoterpene, it is made of two isoprene units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans''-citral) or citral A. The ''Z''-isomer is named neral (''cis''-citral) or citral B. These stereoisomers occur as a mixture, not necessarily racemic; e.g. in essential oil of Australian ginger, the neral to geranial ratio is 0.61. Occurrence Citral is present in the oils of several plants, including lemon myrtle (90–98%), '' Litsea citrata'' (90%), ''Litsea cubeba'' (70–85%), lemongrass (65–85%), lemon tea-tree (70–80%), ''Ocimum gratissimum'' (66.5%), '' Lindera citriodora'' (about 65%), '' Calypranthes parriculata'' (about 62%), petitgrain (36%), lemon verbena (30–35%), lemon ironbark (26%), lemon balm (11%), lime (6–9%), lemon (2–5%), and orange. Further, in the lipid fraction (essential oil) of Australian ginger (51- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinoic Acid
Retinoic acid (used simplified here for all-''trans''-retinoic acid) is a metabolite of vitamin A1 (all-''trans''-retinol) that mediates the functions of vitamin A1 required for growth and development. All-''trans''-retinoic acid is required in chordate animals, which includes all higher animals from fish to humans. During early embryonic development, all-''trans''-retinoic acid generated in a specific region of the embryo helps determine position along the embryonic anterior/posterior axis by serving as an intercellular signaling molecule that guides development of the posterior portion of the embryo. It acts through Hox genes, which ultimately control anterior/posterior patterning in early developmental stages. All-''trans''-retinoic acid (ATRA) is the major occurring retinoic acid, while isomers like 13-''cis''- and 9-''cis''-retinoic acid are also present in much lower levels. The key role of all-''trans''-retinoic acid in embryonic development mediates the high teratogenici ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypostome
In zoology, the hypostome can refer to structures in distinct animal groups: *Hypostome (trilobite), the ventral mouthpart plate in trilobites *Hypostome (tick) The hypostome (also called the maxilla, radula, or labium) is a calcified harpoon-like structure near the mouth area of certain parasitic arthropods including ticks, that allows them to anchor themselves firmly in place on a host vertebrate w ..., the barbed attachment structure associated with the mouthparts of parasitic arachnids * Hypostome (cnidarian), the oral tip surrounded by tentacles in hydrozoan cnidarians {{Set index article ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cnidaria
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Cnidarians mostly have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both (hence they are trimorphic). Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Several free-swimming species of Cubozoa and Scyphozo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
