1.
Taxonomy (biology)
–
Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
2.
Animal
–
Animals are multicellular, eukaryotic organisms of the kingdom Animalia. The animal kingdom emerged as a clade within Apoikozoa as the group to the choanoflagellates. Animals are motile, meaning they can move spontaneously and independently at some point in their lives and their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later in their lives. All animals are heterotrophs, they must ingest other organisms or their products for sustenance, most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates, vertebrates have a backbone or spine, and amount to less than five percent of all described animal species. They include fish, amphibians, reptiles, birds and mammals, the remaining animals are the invertebrates, which lack a backbone. These include molluscs, arthropods, annelids, nematodes, flatworms, cnidarians, ctenophores, the study of animals is called zoology. The word animal comes from the Latin animalis, meaning having breath, the biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects, and humans. Aristotle divided the world between animals and plants, and this was followed by Carl Linnaeus, in the first hierarchical classification. In Linnaeuss original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, in 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms, Metazoa and Protozoa. The protozoa were later moved to the kingdom Protista, leaving only the metazoa, thus Metazoa is now considered a synonym of Animalia. Animals have several characteristics that set apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and they are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at life stages. In most animals, embryos pass through a stage, which is a characteristic exclusive to animals. With a few exceptions, most notably the sponges and Placozoa and these include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals
3.
Chordate
–
Chordates are deuterostomes, as during the embryo development stage the anus forms before the mouth. They are also bilaterally symmetric coelomates, in the case of vertebrate chordates, the notochord is usually replaced by a vertebral column during development, and they may have body plans organized via segmentation. There are also additional extinct taxa, the Vertebrata are sometimes considered as a subgroup of the clade Craniata, consisting of chordates with a skull, the Craniata and Tunicata compose the clade Olfactores. Of the more than 65,000 living species of chordates, the worlds largest and fastest animals, the blue whale and peregrine falcon respectively, are chordates, as are humans. Fossil chordates are known from at least as early as the Cambrian explosion, Hemichordata, which includes the acorn worms, has been presented as a fourth chordate subphylum, but it now is usually treated as a separate phylum. The Hemichordata, along with the Echinodermata, form the Ambulacraria, the Chordata and Ambulacraria form the superphylum Deuterostomia, composed of the deuterostomes. Attempts to work out the relationships of the chordates have produced several hypotheses. All of the earliest chordate fossils have found in the Early Cambrian Chengjiang fauna. Because the fossil record of early chordates is poor, only molecular phylogenetics offers a prospect of dating their emergence. However, the use of molecular phylogenetics for dating evolutionary transitions is controversial and it has also proved difficult to produce a detailed classification within the living chordates. Attempts to produce family trees shows that many of the traditional classes are paraphyletic. While this has been known since the 19th century, an insistence on only monophyletic taxa has resulted in vertebrate classification being in a state of flux. Although the name Chordata is attributed to William Bateson, it was already in prevalent use by 1880, ernst Haeckel described a taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN code because of its subsequent latinization, among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail. In fish and other vertebrates, this develops into the spinal cord, the pharynx is the part of the throat immediately behind the mouth. In fish, the slits are modified to form gills, a muscular tail that extends backwards behind the anus. This is a groove in the wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus and it also stores iodine, and may be a precursor of the vertebrate thyroid gland
4.
Mammal
–
Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles by the possession of a neocortex, hair, three middle ear bones and mammary glands. All female mammals nurse their young with milk, secreted from the mammary glands, Mammals include the largest animals on the planet, the great whales. The basic body type is a quadruped, but some mammals are adapted for life at sea, in the air, in trees. The largest group of mammals, the placentals, have a placenta, Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale. With the exception of the five species of monotreme, all modern mammals give birth to live young, most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents, bats and Soricomorpha, the next three biggest orders, depending on the biological classification scheme used, are the Primates, the Cetartiodactyla, and the Carnivora. Living mammals are divided into the Yinotheria and Theriiformes There are around 5450 species of mammal, in some classifications, extant mammals are divided into two subclasses, the Prototheria, that is, the order Monotremata, and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the group of the Metatheria, and include all living metatherians as well as many extinct ones. Much of the changes reflect the advances of cladistic analysis and molecular genetics, findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora. The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade, the early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the line that led to todays reptiles. Some mammals are intelligent, with some possessing large brains, self-awareness, Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, most mammals are polygynous, but some can be monogamous or polyandrous. They provided, and continue to provide, power for transport and agriculture, as well as commodities such as meat, dairy products, wool. Mammals are hunted or raced for sport, and are used as model organisms in science, Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is accepted, McKenna & Bell and Wilson & Reader provide useful recent compendiums. Though field work gradually made Simpsons classification outdated, it remains the closest thing to a classification of mammals
5.
Even-toed ungulate
–
The even-toed ungulates are ungulates whose weight is borne equally by the third and fourth toes. By contrast, odd-toed ungulates, such as horses, bear their weight primarily on their third toe, the aquatic cetaceans evolved from within even-toed ungulates, and therefore modern taxonomic classification sometimes combines Artiodactyla and Cetacea into Cetartiodactyla. The oldest fossils of even-toed ungulates date back to the early Eocene, since these findings almost simultaneously appeared in Europe, Asia, and North America, it is very difficult to accurately determine the origin of artiodactyls. The fossils are classified as belonging to the family Dichobunidae, their best-known and these were small animals, some as small as a hare, with a slim build, lanky legs, and a long tail. The hind legs were longer than the front legs. The early to middle Eocene saw the emergence of the ancestors of most of todays mammals, two formerly widespread, but now extinct, families of even-toed ungulates were Enteledontidae and Anthracotheriidae. Entelodonts existed from the middle Eocene to the early Miocene in Eurasia and they had a stocky body with short legs and a massive head, which was characterized by two humps on the lower jaw bone. Anthracotheres had a large, porcine build, with short legs and this group appeared in the middle Eocene up until the Pliocene, and spread throughout Eurasia, Africa, and North America. Anthracothereres are thought to be the ancestors of hippos, and, likewise, hippopotamuses appeared in the late Miocene and occupied Africa and Asia – they never got to the Americas. The camels were, during parts of the Cenozoic, limited to North America. Among the North American camels were groups like the stocky, short-legged Merycoidodontidae and they first appeared in the late Eocene and developed a great diversity of species in North America. Only in the late Miocene or early Pliocene did they migrate from North America into Eurasia, the North American varieties became extinct around 10,000 years ago. Suina have been around since the Eocene, in the late Eocene or the Oligocene, two families stayed in Eurasia and Africa, the peccaries, which became extinct in the Old World, exist today only in the Americas. South America was settled by even-toed ungulates only in the Pliocene, with only the peccaries, lamoids, and various species of capreoline deer, South America has comparatively fewer artiodactyl families than other continents. The classification of artiodactyls was hotly debated because the ocean-dwelling cetaceans evolved from the land-dwelling even-toed ungulates, some semiaquatic even-toed ungulates are more closely related to the ocean-dwelling cetaceans than to the other even-toed ungulates. This makes the Artiodactyla as traditionally defined an invalid paraphyletic taxon, since it includes animals descended from a common ancestor, phylogenetic classification only recognizes monophyletic taxa, that is, groups that descend from a common ancestor and include all its descendants. To address this problem, the traditional order Artiodactyla and infraorder Cetacea are sometimes subsumed into the more inclusive Cetartiodactyla taxon, an alternative approach is to include both land-land dwelling even toed ungulates and ocean-dwelling cetaceans in a revised Artiodactyla taxon. Order Artiodactyla/Clade CetartiodactylaSuborder Tylopoda Family †Anoplotheriidae, molecular biology involves sequencing an organisms DNA and RNA and comparing the sequence with that of other living beings – the more similar they are, the more closely they are related
6.
Cetacea
–
Cetacea are a widely distributed and diverse clade of aquatic mammals that today consists of the whales, dolphins, and porpoises. Most species live in the sea, some in rivers, the name is derived from the Latin cetus whale and Greek ketos huge fish. The extinct ancestors of modern whales are the Archaeoceti, while cetaceans were historically thought to have descended from mesonychids, molecular evidence supports them as a relative of Artiodactyls. Cetaceans belong to the order Cetartiodactyla and their closest living relatives are hippopotamuses and other hoofed mammals, having diverged about 50 million years ago. Cetaceans range in size from the 1 m and 50 kg Mauis dolphin to the 29.9 m and 190,000 kg blue whale and they have streamlined bodies and two limbs that are modified into flippers. Dolphins are able to very tight turns while swimming at high speeds. The hindlimbs of cetaceans are internal, and are thought to be vestigial, baleen whales have short hairs on their mouth, unlike the toothed whales. Cetaceans have well-developed senses—their eyesight and hearing are adapted for both air and water, and baleen whales have a system in their vibrissae. They have a layer of fat, or blubber, under the skin to maintain body heat in cold water, Some species are well adapted for diving to great depths. Although cetaceans are widespread, most species prefer the waters of the Northern and Southern Hemispheres. They spend their lives in the water, having to mate, give birth, molt or escape predators, like killer whales. This has drastically affected their anatomy to be able to do so and they feed largely on fish and marine invertebrates, but a few, like the killer whale, feed on large mammals and birds, such as penguins and seals. Some baleen whales are specialised for feeding on benthic creatures, male cetaceans typically mate with more than one female, although the degree of polygyny varies with the species. Cetaceans are not shown to have pair bonds, male cetacean strategies for reproductive success vary between herding females, defending potential mates from other males, or whale song which attracts mates. Calves are typically born in the fall and winter months, cetaceans produce a number of vocalizations, notably the clicks and whistles of dolphins, the moaning songs of the humpback whale. The meat, blubber and oil of cetaceans have traditionally used by indigenous peoples of the Arctic. Cetaceans have been depicted in cultures worldwide. Dolphins are commonly kept in captivity and are sometimes trained to perform tricks and tasks
7.
Oceanic dolphin
–
Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. They include several big species whose common names contain whale rather than dolphin, such as the killer whale, Delphinidae is a family within the superfamily Delphinoidea, which also includes the porpoises and the Monodontidae. River dolphins are relatives of the Delphinoidea, oceanic dolphins range in size from the 5. 6-foot -long and 110-pound Mauis dolphin to the 31-foot and 11-short-ton killer whale, the largest known dolphin. Several species exhibit sexual dimorphism, the males are larger than females and they have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, some dolphins can travel at 34.5 mph and they typically have between 100 and 200 teeth, although a few species have considerably fewer. Delphinids travel in pods, which may number a thousand individuals in some species. Each pod forages over a range of a few dozen to a few hundred square miles, some pods have a loose social structure, with individuals frequently joining or leaving, but others seem to be more permanent, perhaps dominated by a male and a harem of females. Individuals communicate by sound, producing low-frequency whistles, and also produce high-frequency broadband clicks of 80-220 kHz, gestation lasts from 10 to 18 months, and results in the birth of a single calf. Some species are adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water, although oceanic dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Some have a distribution, like the killer whale. Oceanic dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer, and females bear all the responsibility for raising them, mothers of some species fast and nurse their young for relatively long times. Dolphins produce a variety of vocalizations, usually in the form of clicks, oceanic dolphins are sometimes hunted in places such as Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they face threats from bycatch, habitat loss. Dolphins have been depicted in cultures worldwide. They occasionally feature in literature and film, as in the Warner Bros film Free Willy, oceanic dolphins are kept in captivity and trained to perform tricks, but breeding success has been poor and the animals often die within a few months of capture. The most common dolphins kept are the whales and bottlenose dolphins
8.
Dolphin
–
Dolphins are a widely distributed and diverse group of aquatic mammals. They are a grouping within the order Cetacea, excluding whales and porpoises. The dolphins comprise the extant families Delphinidae, Platanistidae, Iniidae, and Pontoporiidae, there are 40 extant species of dolphins. Dolphins, alongside other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates and their closest living relatives are the hippopotamuses, having diverged about 40 million years ago. Dolphins range in size from the 1.7 m long and 50 kg Mauis dolphin to the 9.5 m and 10 t killer whale, several species exhibit sexual dimorphism, in that the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers, though not quite as flexible as seals, some dolphins can travel at 55.5 km/h. Dolphins use their conical shaped teeth to capture fast moving prey and they have well-developed hearing which is adapted for both air and water and is so well developed that some can survive even if they are blind. Some species are adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water, although dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them, mothers of some species fast and nurse their young for a relatively long period of time. Dolphins produce a variety of vocalizations, usually in the form of clicks, Dolphins are sometimes hunted in places like Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they face threats from bycatch, habitat loss. Dolphins have been depicted in cultures worldwide. Dolphins occasionally feature in literature and film, as in the film series Free Willy, Dolphins are sometimes kept in captivity and trained to perform tricks, but breeding success has been poor and the animals often die within a few months of capture. The most common dolphins kept are killer whales and bottlenose dolphins, the name is originally from Greek δελφίς, dolphin, which was related to the Greek δελφύς, womb. The animals name can therefore be interpreted as meaning a fish with a womb, the name was transmitted via the Latin delphinus, which in Medieval Latin became dolfinus and in Old French daulphin, which reintroduced the ph into the word. The term mereswine has also historically been used, the term dolphin can be used to refer to, under the parvorder Odontoceti, all the species in the family Delphinidae and the river dolphin families Iniidae, Pontoporiidae, Lipotidae and Platanistidae
9.
Cestoda
–
Cestoda is a class of parasitic flatworms of the phylum Platyhelminthes. Biologists informally refer to them as cestodes, the best-known species are commonly called tapeworms. All cestodes are parasitic and their life histories vary, but typically they live in the tracts of vertebrates as adults. Over a thousand species have been described, and all species may be parasitised by at least one species of tapeworm. Humans are subject to infection by several species of tapeworms if they eat undercooked meat such as pork, beef, and fish, or if they live in, or eat food prepared in, conditions of poor hygiene. T. saginata, the tapeworm, can grow up to 20 m, the largest species. Species using small vertebrates as hosts, though, tend to be small, for example, vole and lemming tapeworms are only 13–240 mm in length, and those parasitizing shrews only 0. 8–60 mm. The worms scolex attaches to the intestine of the definitive host, in some species, the scolex is dominated by bothria, or sucking grooves that function like suction cups. Other species have hooks and suckers that aid in attachment, cyclophyllid cestodes can be identified by the presence of four suckers on their scolices. While the scolex is often the most distinctive part of a tapeworm, it is often unnoticed in a clinical setting. Therefore, identifying eggs and proglottids in feces is the simplest way to diagnose an infection, the main nerve centre of a cestode is a cerebral ganglion in its scolex. Motor and sensory innervation depends on the number of nerves in, smaller nerves emanate from the ganglion to supply the general body muscular and sensory ending. The cirrus and vagina are innervated, and sensory endings around the genital pore are more plentiful than other areas, sensory function includes both tactoreception and chemoreception. The body is composed of segments called proglottids. The sum of the proglottids is called a strobila, which is thin, from this is derived the common name tapeworm. Proglottids are continually produced by the region of the scolex, as long as the scolex is attached. Like some other flatworms, cestodes use flame cells, located in the proglottids, mature proglottids are released from the tapeworms end segment and leave the host in feces or migrate as independent motile proglottids. The proglottids farthest away from the scolex are the ones containing eggs
10.
Acanthocephala
–
Acanthocephalans have complex life cycles, involving at least two hosts, which may include invertebrates, fish, amphibians, birds, and mammals. About 1150 species have been described, the Acanthocephala were thought to be a discrete phylum. Recent genome analysis has shown that they are descended from, and should be considered as and this finding is an example of molecular phylogenetics. This unified taxon is known as Syndermata, the earliest recognisable description of Acanthocephala – a worm with a proboscis armed with hooks – was made by Italian author Francesco Redi. In 1771, Joseph Koelreuter proposed the name Acanthocephala, philipp Ludwig Statius Müller independently called them Echinorhynchus in 1776. Karl Rudolphi in 1809 formally named them Acanthocephala, acanthocephalans are highly adapted to a parasitic mode of life, and have lost many organs and structures through evolutionary processes. This makes determining relationships with other higher taxa through morphological comparison problematic, phylogenetic analysis of the 18S ribosomal gene has revealed that the Acanthocephala are most closely related to the rotifers. They are possibly closer to the two rotifer classes Bdelloidea and Monogononta than to the class, Seisonidea, producing the names. The three rotifer classes and the Acanthocephala make up a clade called Syndermata and this clade is placed in the Platyzoa. Currently the phylum is divided into four classes – Palaeacanthocephala, Archiacanthocephala, Polyacanthocephala and Eoacanthocephala, the monophyletic Archiacanthocephala are the sister taxon of a clade comprising Eoacanthocephala and the monophyletic Palaeacanthocephala. A study of the order in the mitochondria suggests that Seisonidea and Acanthocephala are sister clades. There are several characteristics that distinguish acanthocephalans from other phyla of parasitic worms. Acanthocephalans lack a mouth or alimentary canal and this is a feature they share with the cestoda, although the two groups are not closely related. Adult stages live in the intestines of their host and uptake nutrients which have been digested by the host, directly, the most notable feature of the acanthocephala is the presence of an anterior, protrudible proboscis that is usually covered with spiny hooks. The proboscis bears rings of recurved hooks arranged in horizontal rows, the proboscis is used to pierce the gut wall of the final host, and hold the parasite fast while it completes its life cycle. Like the body, the proboscis is hollow, and its cavity is separated from the cavity by a septum or proboscis sheath. Traversing the cavity of the proboscis are muscle-strands inserted into the tip of the proboscis at one end and their contraction causes the proboscis to be invaginated into its cavity. Some of the acanthocephalans can insert their proboscis in the intestine of the host, the size of these animals varies greatly, some are measured to be a few millimetres in length to Gigantorhynchus gigas, which measures from 10 to 65 centimetres
11.
Seine fishing
–
Seine fishing is a method of fishing that employs a seine or dragnet. A seine is a net that hangs vertically in the water with its bottom edge held down by weights and its top edge buoyed by floats. Seine nets can be deployed from the shore as a beach seine, boats deploying seine nets are known as seiners. There are two types of seine net deployed from seiners, purse seines and Danish seines. Seine, or Sean, according to Encyclopedia Britannica in 1926, seines have been used widely in the past, including by stone age societies. For example, with the help of large canoes, pre-European Māori deployed seine nets which could be one thousand metres long. The nets were woven from green flax, with weights and light wood or gourd floats. Native Americans on the Columbia River wove seine nets from spruce root fibers or wild grass, for floats they used sticks made of cedar which moved in a way which frightened the fish and helped keep them together. Seine nets are well documented in ancient cultures in the Mediterranean region. They appear in Egyptian tomb paintings from 3000 BC, in ancient Greek literature, Ovid makes many references to seine nets, including the use of cork floats and lead weights. A common type of seine is a purse seine, named such because along the bottom are a number of rings. A line passes through all the rings, and when pulled, draws the rings close to one another, preventing the fish from sounding and this operation is similar to a traditional style purse, which has a drawstring. Boats equipped with purse seines are called purse seiners, Purse seine fishing can be a relatively sustainable way of fishing, as it can result in smaller amounts of by-catch, especially when used to catch large species of fish that shoal tightly together. When used to fish that shoal together with other species, or when used in parallel with fish aggregating devices. Use of purse seines is regulated by many countries, in Sri Lanka, using this type of net within 7 kilometers of the shore is illegal. However, they can be used in the sea, after obtaining permission from authorities. Purse seine fishing can have impacts on fish stocks because it can involve the bycatch of non-target species. The power block is a pulley used on some seiners to haul in the nets
12.
Dichlorodiphenyltrichloroethane
–
Dichlorodiphenyltrichloroethane is a colorless, crystalline, tasteless, and almost odorless organochlorine known for its insecticidal properties and environmental impacts. First synthesized in 1874, DDTs insecticidal action was discovered by the Swiss chemist Paul Hermann Müller in 1939 and it was used in the second half of World War II to control malaria and typhus among civilians and troops. After the war, DDT was also used as an insecticide and its production. Müller was awarded the Nobel Prize in Physiology or Medicine for his discovery of the efficiency of DDT as a contact poison against several arthropods in 1948. In 1962, Rachel Carsons book Silent Spring was published, the book claimed that DDT and other pesticides had been shown to cause cancer and that their agricultural use was a threat to wildlife, particularly birds. Its publication was an event for the environmental movement and resulted in a large public outcry that eventually led, in 1972. DDT is similar in structure to the insecticide methoxychlor and the acaricide dicofol and it is highly hydrophobic and nearly insoluble in water but has good solubility in most organic solvents, fats and oils. It is produced by the reaction of chloral with chlorobenzene in the presence of an acid catalyst. DDT has been marketed under names including Anofex, Cezarex, Chlorophenothane, Clofenotane, Dicophane, Dinocide, Gesarol, Guesapon, Guesarol, Gyron, Ixodex, Neocid, Neocidol. Commercial DDT is a mixture of several closely–related compounds, the major component is the p, p isomer. The o, p isomer is present in significant amounts. Dichlorodiphenyldichloroethylene and dichlorodiphenyldichloroethane make up the balance, DDE and DDD are the major metabolites and environmental breakdown products. In the United States, it was manufactured by some 15 companies, including Monsanto, Ciba, Montrose Chemical Company, Pennwalt, production peaked in 1963 at 82,000 tonnes per year. More than 600,000 tonnes were applied in the US before the 1972 ban, usage peaked in 1959 at about 36,000 tonnes. In 2009,3,314 tonnes were produced for malaria control, India is the only country still manufacturing DDT and is the largest consumer. In insects it opens sodium ion channels in neurons, causing them to fire spontaneously, insects with certain mutations in their sodium channel gene are resistant to DDT and similar insecticides. Genomic studies in the model genetic organism Drosophila melanogaster revealed that high level DDT resistance is polygenic, DDT was first synthesized in 1874 by Othmar Zeidler under the supervision of Adolf von Baeyer. It was further described in 1929 in a dissertation by W. Bausch, the insecticide properties of multiple chlorinated aliphatic or fat-aromatic alcohols with at least one trichloromethane group were described in a patent in 1934 by Wolfgang von Leuthold
.jpg)
