Cnidaria is a phylum under Kingdom Animalia containing over 11,000 species of animals found in aquatic environments: they are predominantly marine. Their distinguishing feature is cnidocytes, specialized cells that they use for capturing prey, their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are one cell thick. They 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 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. Cnidarians' activities are coordinated by simple receptors. Several free-swimming species of Cubozoa and Scyphozoa possess balance-sensing statocysts, some have simple eyes. Not all cnidarians reproduce sexually, with many species having complex life cycles of asexual polyp stages and sexual medusae.
Some, omit either the polyp or the medusa stage. Cnidarians were grouped with ctenophores in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla. Cnidarians are classified into four main groups: the wholly sessile Anthozoa. Staurozoa have been recognised as a class in their own right rather than a sub-group of Scyphozoa, the parasitic Myxozoa and Polypodiozoa were only recognized as cnidarians in 2007. Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from dinoflagellates, a few are parasites. Many are preyed on by other animals including starfish, sea slugs, fish and other cnidarians. Many scleractinian corals—which form the structural foundation for coral reefs—possess polyps that are filled with symbiotic photo-synthetic zooxanthellae. While reef-forming corals are entirely restricted to warm and shallow marine waters, other cnidarians can be found at great depths, in polar regions, in freshwater.
Recent phylogenetic analyses support monophyly of cnidarians, as well as the position of cnidarians as the sister group of bilaterians. Fossil cnidarians have been found in rocks formed about 580 million years ago, other fossils show that corals may have been present shortly before 490 million years ago and diversified a few million years later. However, molecular clock analysis of mitochondrial genes suggests a much older age for the crown group of cnidarians, estimated around 741 million years ago 200 million years before the Cambrian period as well as any fossils. Cnidarians form a phylum of animal that are more complex than sponges, about as complex as ctenophores, less complex than bilaterians, which include all other animals. Both cnidarians and ctenophores are more complex than sponges as they have: cells bound by inter-cell connections and carpet-like basement membranes. Cnidarians are distinguished from all other animals by having cnidocytes that fire harpoon like structures and are used to capture prey.
In some species, cnidocytes can be used as anchors. Like sponges and ctenophores, cnidarians have two main layers of cells that sandwich a middle layer of jelly-like material, called the mesoglea in cnidarians. Hence and ctenophores have traditionally been labelled diploblastic, along with sponges. However, both cnidarians and ctenophores have a type of muscle that, in more complex animals, arises from the middle cell layer; as a result, some recent text books classify ctenophores as triploblastic, it has been suggested that cnidarians evolved from triploblastic ancestors. Most adult cnidarians appear as either free-swimming medusae or sessile polyps, many hydrozoans species are known to alternate between the two forms. Both are radially symmetrical, like a tube respectively. Since these animals have no heads, their ends are described as "oral" and "aboral". Most have fringes of tentacles equipped with cnidocytes around their edges, medusae have an inner ring of tentacles around the mouth; some hydroids may consist of colonies of zooids that serve different purposes, such as defense and catching prey.
The mesoglea of polyps is thin and soft, but that of medusae is thick and springy, so that it returns to its original shape after muscles around the edge have contracted to squeeze water out, enabling medusae to swim by a sort of jet propulsion. In medusae the only supporting structure is the mesoglea. Hydra and most sea anemones close their mouths when they are not feeding, the water in the digestive cavity acts as a hydrostatic skeleton, rather like a water-filled balloon. Other polyps such as Tubularia use columns of water-filled cells for support. Sea pens stiffen the mesoglea with calcium carbonate spicules and tough fibrous proteins, rather like sponges. In some colonial polyps, a chitinous periderm gives support and some protection to the connecting sections and to the lower parts of individual polyps. Stony corals secrete massive calcium carbonate exoske
Cristatella mucedo is a bryozoan in the family Cristatellidae, the only species of the genus Cristatella. The species can be found in north-eastern North America, Northern Europe, including United Kingdom, Norway and the Netherlands from sea level to 1,116 metres asl; the species prefers cold climate waters. They live in statoblastic colonies; the habitat is either lentic, including man-made water bodies such as gravel pits. Populations in Europe are genetically homogeneous reflecting postglacial colonization representing a single lineage. In contrasts, North American populations are diverse. There is some evidence of two different major lineages representing cryptic species or subspecies, with hybridization that have boosted genetic diversity
Etymology is the study of the history of words. By extension, the term "the etymology" means the origin of the particular word and for place names, there is a specific term, toponymy. For Greek—with a long written history—etymologists make use of texts, texts about the language, to gather knowledge about how words were used during earlier periods and when they entered the language. Etymologists apply the methods of comparative linguistics to reconstruct information about languages that are too old for any direct information to be available. By analyzing related languages with a technique known as the comparative method, linguists can make inferences about their shared parent language and its vocabulary. In this way, word roots have been found that can be traced all the way back to the origin of, for instance, the Indo-European language family. Though etymological research grew from the philological tradition, much current etymological research is done on language families where little or no early documentation is available, such as Uralic and Austronesian.
The word etymology derives from the Greek word ἐτυμολογία, itself from ἔτυμον, meaning "true sense", the suffix -logia, denoting "the study of". In linguistics, the term etymon refers to a word or morpheme from which a word derives. For example, the Latin word candidus, which means "white", is the etymon of English candid. Etymologists apply a number of methods to study the origins of words, some of which are: Philological research. Changes in the form and meaning of the word can be traced with the aid of older texts, if such are available. Making use of dialectological data; the form or meaning of the word might show variations between dialects, which may yield clues about its earlier history. The comparative method. By a systematic comparison of related languages, etymologists may be able to detect which words derive from their common ancestor language and which were instead borrowed from another language; the study of semantic change. Etymologists must make hypotheses about changes in the meaning of particular words.
Such hypotheses are tested against the general knowledge of semantic shifts. For example, the assumption of a particular change of meaning may be substantiated by showing that the same type of change has occurred in other languages as well. Etymological theory recognizes that words originate through a limited number of basic mechanisms, the most important of which are language change, borrowing. While the origin of newly emerged words is more or less transparent, it tends to become obscured through time due to sound change or semantic change. Due to sound change, it is not obvious that the English word set is related to the word sit, it is less obvious that bless is related to blood. Semantic change may occur. For example, the English word bead meant "prayer", it acquired its modern meaning through the practice of counting the recitation of prayers by using beads. English derives from Old English, a West Germanic variety, although its current vocabulary includes words from many languages; the Old English roots may be seen in the similarity of numbers in English and German seven/sieben, eight/acht, nine/neun, ten/zehn.
Pronouns are cognate: I/mine/me and ich/mein/mich. However, language change has eroded many grammatical elements, such as the noun case system, simplified in modern English, certain elements of vocabulary, some of which are borrowed from French. Although many of the words in the English lexicon come from Romance languages, most of the common words used in English are of Germanic origin; when the Normans conquered England in 1066, they brought their Norman language with them. During the Anglo-Norman period, which united insular and continental territories, the ruling class spoke Anglo-Norman, while the peasants spoke the vernacular English of the time. Anglo-Norman was the conduit for the introduction of French into England, aided by the circulation of Langue d'oïl literature from France; this led to many paired words of English origin. For example, beef is related, through borrowing, to modern French bœuf, veal to veau, pork to porc, poultry to poulet. All these words and English, refer to the meat rather than to the animal.
Words that refer to farm animals, on the other hand, tend to be cognates of words in other Germanic languages. For example, swine/Schwein, cow/Kuh, calf/Kalb, sheep/Schaf; the variant usage has been explained by the proposition that it was the Norman rulers who ate meat and the Anglo-Saxons who farmed the animals. This explanation has been disputed. English has proved accommodating to words from many languages. Scientific terminology, for example, relies on words of Latin and Greek origin, but there are a great many non-scientific examples. Spanish has contributed many words in the southwestern United States. Examples include buckaroo, rodeo and states' names such as Colorado and Florida. Albino, lingo and coconut from Portuguese. Modern French has contributed café, naive and many more. Smorgasbord, slalom
Myxobolus cerebralis is a myxosporean parasite of salmonids that causes whirling disease in farmed salmon and trout and in wild fish populations. It was first described in rainbow trout in Germany a century ago, but its range has spread and it has appeared in most of Europe, the United States, South Africa and other countries. In the 1980s, M. cerebralis was found to require a tubificid oligochaete to complete its life cycle. The parasite infects its hosts with its cells after piercing them with polar filaments ejected from nematocyst-like capsules. Whirling disease causes skeletal deformation and neurological damage. Fish "whirl" forward in an awkward, corkscrew-like pattern instead of swimming find feeding difficult, are more vulnerable to predators; the mortality rate is high for fingerlings, up to 90% of infected populations, those that do survive are deformed by the parasites residing in their cartilage and bone. They act as a reservoir for the parasite, released into water following the fish's death.
M. cerebralis is one of the most economically important myxozoans in fish, as well as one of the most pathogenic. It was the first myxosporean; the parasite is not transmissible to humans. The taxonomy and naming of both M. cerebralis, of myxozoans in general, have complicated histories. It was thought to infect fish brains and nervous systems, though it soon was found to infect cartilage and skeletal tissue. Attempts to change the name to Myxobolus chondrophagus, which would more describe the organism, failed because of nomenclature rules; the organisms called Triactinomyxon dubium and T. gyrosalmo were found to be, in fact, triactinomyxon stages of M. cerebralis, the life cycle of, expanded to include the triactinomyxon stage. Other actinosporeans were folded into the life cycles of various myxosporeans. Today, the myxozoans thought to be multicellular protozoans, are considered animals by most scientists, though their status has not changed. Recent molecular studies suggest they are related to Bilateria or Cnidaria, with Cnidaria being closer morphologically because both groups have extrusive filaments.
Bilateria were somewhat closer in some genetic studies, but those were found to have used samples that were contaminated by material from the host organism, a 2015 study confirms they are cnidarians. M. cerebralis has many diverse stages ranging from single cells to large spores, not all of which have been studied in detail. The stages that infect fish, called triactinomyxon spores, are made of a single style, about 150 micrometers long and three processes or "tails", each about 200 micrometers long. A sporoplasm packet at the end of the style contains 64 germ cells surrounded by a cellular envelope. There are three polar capsules, each of which contains a coiled polar filament between 170 and 180 µm long. Polar filaments in both this stage and in the myxospore stage shoot into the body of the host, creating an opening through which the sporoplasm can enter. Upon contact with fish hosts and firing of the polar capsules, the sporoplasm contained within the central style of the triactinomyxon migrates into the epithelium or gut lining.
Firstly, this sporoplasm undergoes mitosis to produce more amoeboid cells, which migrate into deeper tissue layers, to reach the cerebral cartilage. Myxospores, which develop from sporogonic cell stages inside fish hosts, are lenticular, they are made of six cells. Two of these cells form polar capsules, two merge to form a binucleate sporoplasm, two form protective valves. Myxospores are infective to oligochaetes, are found among the remains of digested fish cartilage, they are difficult to distinguish from related species because of morphological similarities across genera. Though M. cerebralis is the only myxosporean found in salmonid cartilage, other visually similar species may be present in the skin, nervous system, or muscle. Myxobolus cerebralis has a two-host life cycle involving a salmonid fish and a tubificid oligochaete. So far, the only worm known to be susceptible to M. cerebralis infection is Tubifex tubifex, though what scientists call T. tubifex may in fact be more than one species.
First, myxospores are ingested by tubificid worms. In the gut lumen of the worm, the spores extrude their polar capsules and attach to the gut epithelium by polar filaments; the shell valves open along the suture line and the binucleate germ cell penetrates between the intestinal epithelial cells of the worm. This cell multiplies, producing many amoeboid cells by an asexual cell fission process called merogony; as a result of the multiplication process, the intercellular space of the epithelial cells in more than 10 neighbouring worm segments may become infected. Around 60–90 days postinfection, sexual cell stages of the parasite undergo sporogenesis, develop into pansporocysts, each of which contains eight triactinomyxon-stage spores; these spores are released from the oligochaete anus into the water. Alternatively, a fish can become infected by eating an infected oligochaete. Infected tubificids can release triactinomyxons for at least a year; the triactinomyxon spores are carried by the water currents, where they can infect a salmonid through the skin.
Penetration of the fish by these spores takes only a few seconds. Within five minutes, a sac of germ cells called a sporoplasm has entered the fish epidermis, within a