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Xenoturbellida
''Xenoturbella'' is a genus of very simple bilaterians up to a few centimeters long. It contains a small number of marine benthos, benthic worm-like species. The first known species (''Xenoturbella bocki'') was collected in 1878 and 1879 in the Gullmar fiord on the Swedish west coast by August Malm and is stored in the collection of the Gothenburg Natural History Museum. A specimen is on display in the exhibition. It was collected again in the Gullmar fiord in 1915 by Sixten Bock, but it was only properly described in 1949 by Einar Westblad. The type specimens are kept at the Swedish Museum of Natural History in Stockholm. Description ''Xenoturbella'' has a very simple body plan. It consists of a dorsoventrally flattened coelom#Acoelomates, acoelomate body, with a ventral furrow on each side running down from the anterior tip till they are stopped by an anterior circumferential furrow. It shows two ciliated epithelium, epithelial layers: an external epidermis (zoology), epidermi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xenoturbella Bocki
''Xenoturbella bocki'' is a marine benthos, benthic worm-like species from the genus ''Xenoturbella''. It is found in saltwater sea floor habitats off the coast of Europe, predominantly Sweden. It was the first species in the genus discovered. Initially it was collected by Swedish zoologist Sixten Bock in 1915, and described in 1949 by Swedish zoologist Einar Westblad. The unusual digestive structure of this species, in which a single opening is used to eat food and excrete waste, has led to considerable study and controversy as to its classification. It is a bottom-dwelling, burrowing carnivore that eats mollusks (likely larval forms, as opposed to hard-shelled adults). Systematics Etymology For the genus name ''Xenoturbella'', Ancient Greek ''xénos'', means foreign or strange, and Latin , means a bustle or turbulence in water. Genus ''Xenoturbella'' is a member of sub-phylum Xenoturbellida, which are known as – Swedish for "paradox worms" (a term that some popular media ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xenoturbella Bockii Longitudinal Section English
''Xenoturbella'' is a genus of very simple bilaterians up to a few centimeters long. It contains a small number of marine benthic worm-like species. The first known species (''Xenoturbella bocki'') was collected in 1878 and 1879 in the Gullmar fiord on the Swedish west coast by August Malm and is stored in the collection of the Gothenburg Natural History Museum. A specimen is on display in the exhibition. It was collected again in the Gullmar fiord in 1915 by Sixten Bock, but it was only properly described in 1949 by Einar Westblad. The type specimens are kept at the Swedish Museum of Natural History in Stockholm. Description ''Xenoturbella'' has a very simple body plan. It consists of a dorsoventrally flattened acoelomate body, with a ventral furrow on each side running down from the anterior tip till they are stopped by an anterior circumferential furrow. It shows two ciliated epithelial layers: an external epidermis and an internal gastrodermis lining the simple sac-like g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nervous System
In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events. Nervous tissue first arose in Ediacara biota, wormlike organisms about 550 to 600 million years ago. In Vertebrate, vertebrates, it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers, or axons, that connect the CNS to every other part of the body. Nerves that transmit signals from the brain are called motor nerves (efferent), while those nerves that transmit information from the body to the CNS are called sensory nerves (aff ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bilateria
Bilateria () is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left–right–symmetrical belly ( ventral) and back ( dorsal) surface. Nearly all bilaterians maintain a bilaterally symmetrical body as adults; the most notable exception is the echinoderms, which have pentaradial symmetry as adults, but bilateral symmetry as embryos. With few exceptions, bilaterian embryos are triploblastic, having three germ layers: endoderm, mesoderm and ectoderm, and have complete digestive tracts with a separate mouth and anus. Some bilaterians lack body cavities, while others have a primary body cavity derived from the blastocoel, or a secondary cavity, the coelom. Cephalization is a characteristic feature among most bilaterians, where the sense organs and central nerve ganglia become concentrated at th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gamete
A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the German cytologist Eduard Strasburger in 1878. Gametes of both mating individuals can be the same size and shape, a condition known as isogamy. By contrast, in the majority of species, the gametes are of different sizes, a condition known as anisogamy or heterogamy that applies to humans and other mammals. The human ovum has approximately 100,000 times the volume of a single human sperm cell. The type of gamete an organism produces determines its sex and sets the basis for the sexual roles and sexual selection. In humans and other species that produce two Morphology (biology), morphologically distinct types of gametes, and in which Gonochorism, each individual produces only one type, a femal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Excretory System
The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, so as to help maintain internal chemical homeostasis and prevent damage to the body. The dual function of excretory systems is the elimination of the waste products of metabolism and to drain the body of used up and broken down components in a liquid and gaseous state. In humans and other amniotes (mammals, birds and reptiles), most of these substances leave the body as urine and to some degree exhalation, mammals also expel them through sweating. Only the organs specifically used for the excretion are considered a part of the excretory system. In the narrow sense, the term refers to the urinary system. However, as excretion involves several functions that are only superficially related, it is not usually used in more formal classifications of anatomy or function. As most healthy functioning organs produce metabolic and other wastes, the entire o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organ (anatomy)
In a multicellular organism, an organ is a collection of Tissue (biology), tissues joined in a structural unit to serve a common function. In the biological organization, hierarchy of life, an organ lies between Tissue (biology), tissue and an organ system. Tissues are formed from same type Cell (biology), cells to act together in a function. Tissues of different types combine to form an organ which has a specific function. The Gastrointestinal tract, intestinal wall for example is formed by epithelial tissue and smooth muscle tissue. Two or more organs working together in the execution of a specific body function form an organ system, also called a biological system or body system. An organ's tissues can be broadly categorized as parenchyma, the functional tissue, and stroma (tissue), stroma, the structural tissue with supportive, connective, or ancillary functions. For example, the gland's tissue that makes the hormones is the parenchyma, whereas the stroma includes the nerve t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, crustaceans, and gastropods, A similar structure is also found in '' Xenoturbella''. The statocyst consists of a sac-like structure containing a mineralised mass (statolith) and numerous innervated sensory hairs ( setae). The statolith's inertia causes it to push against the setae when the animal accelerates. Deflection of setae by the statolith in response to gravity activates neurons, providing feedback to the animal on change in orientation and allowing balance to be maintained. In other words, the statolith shifts as the animal moves. Any movement large enough to throw the organism off balance causes the statolith to brush against tiny bristles which in turn send a message to the brain to correct its balance. It may have been present in the common ancestor of cnidarians and bilaterians. Hearing In cephalopods like s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gonad
A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sperm in the form of Spermatozoon, spermatozoa. The female gonad, the ovary, produces egg cells. Both of these gametes are haploid cells. Some hermaphroditic animals (and some humanssee Ovotesticular syndrome) have a type of gonad called an ovotestis. Evolution It is hard to find a common origin for gonads, but gonads most likely evolved independently several times. Regulation The gonads are controlled by luteinizing hormone (LH) and follicle-stimulating hormone (FSH), produced and secreted by gonadotropic cell, gonadotropes or gonadotrophins in the anterior pituitary gland. This secretion is regulated by gonadotropin-releasing hormone (GnRH) produced in the hypothalamus. Development The gonads develop f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nemertodermatida
Nemertodermatida is a class of Acoelomorpha, comprising 18 species of millimetre-sized turbellariform, mostly interstitial worms. Taxonomy The order Nemertodermatida contains two families with 6 genera. The high level of cryptic diversity in this meiofauna group however implies that the number of nemertodermatid taxa may be underestimated. Ascopariidae The family Ascopariidae Sterrer, 1998 contains two genera. * '' Ascoparia'' Sterrer, 1998 * '' Flagellophora'' Faubel & Dorjes, 1978 There are 3 species in the family ''Ascopariidae''. Nemertodermatidae The family Nemertodermatidae Steinböck, 1930 contains four genera. * '' Meara'' * '' Nemertinoides'' * '' Nemertoderma'' * '' Sterreria'' There are 15 species in the family ''Nemertodermatidae''. Notes References Animal classes {{Xenacoelomorpha-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embryo
An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres. The blastomeres (4-cell stage) are arranged as a solid ball that when reaching a certain size, called a morula, (16-cell stage) takes in fluid to create a cavity called a blastocoel. The structure is then termed a blastula, or a blastocyst in mammals. The mammalian blastocyst hatches before implantating into the endometrial lining of the womb. Once implanted the embryo will continue its development through the next stages of gastrulation, neurulation, and organogenesis. Gastrulation is the formation of the three germ layers that will form all of the different parts of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acoela
Acoela, or the acoels, is an order of small and simple invertebrates in the subphylum Acoelomorpha of phylum Xenacoelomorpha, a deep branching bilaterian group of animals, which resemble flatworms. Historically they were treated as an order of turbellarian flatworms. About 400 species are known, but probably many more not yet described. The etymology of "acoel" is from the Ancient Greek words (), the '' alpha privative'', expressing negation or absence, and (), meaning "cavity". This refers to the fact that acoels have a structure lacking a fluid-filled body cavity. Description Acoels are very small flattened worms, usually under in length, but some larger species, such as '' Symsagittifera roscoffensis'', may reach up to . They are bilaterally symmetric and microscopic. They are found worldwide in marine and brackish waters, usually having a benthic lifestyle, although some species are epibionts. Two species, ''Limnoposthia polonica'' and ''Oligochoerus limnophilus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
