A scientist is someone who conducts scientific research to advance knowledge in an area of interest. In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engaged in the philosophical study of nature called natural philosophy, a precursor of natural science, it was not until the 19th century that the term scientist came into regular use after it was coined by the theologian and historian of science William Whewell in 1833. The term'scientist' was first coined by him for Mary Somerville because the term "man of science", more custom at that time, was inappropriate here. In modern times, many scientists have advanced degrees in an area of science and pursue careers in various sectors of the economy such as academia, industry and nonprofit environments; the roles of "scientists", their predecessors before the emergence of modern scientific disciplines, have evolved over time. Scientists of different eras have had different places in society, the social norms, ethical values, epistemic virtues associated with scientists—and expected of them—have changed over time as well.
Accordingly, many different historical figures can be identified as early scientists, depending on which characteristics of modern science are taken to be essential. Some historians point to the Scientific Revolution that began in 16th century as the period when science in a recognizably modern form developed, it wasn't until the 19th century that sufficient socioeconomic changes occurred for scientists to emerge as a major profession. Knowledge about nature in classical antiquity was pursued by many kinds of scholars. Greek contributions to science—including works of geometry and mathematical astronomy, early accounts of biological processes and catalogs of plants and animals, theories of knowledge and learning—were produced by philosophers and physicians, as well as practitioners of various trades; these roles, their associations with scientific knowledge, spread with the Roman Empire and, with the spread of Christianity, became linked to religious institutions in most of European countries.
Astrology and astronomy became an important area of knowledge, the role of astronomer/astrologer developed with the support of political and religious patronage. By the time of the medieval university system, knowledge was divided into the trivium—philosophy, including natural philosophy—and the quadrivium—mathematics, including astronomy. Hence, the medieval analogs of scientists were either philosophers or mathematicians. Knowledge of plants and animals was broadly the province of physicians. Science in medieval Islam generated some new modes of developing natural knowledge, although still within the bounds of existing social roles such as philosopher and mathematician. Many proto-scientists from the Islamic Golden Age are considered polymaths, in part because of the lack of anything corresponding to modern scientific disciplines. Many of these early polymaths were religious priests and theologians: for example, Alhazen and al-Biruni were mutakallimiin. During the Italian Renaissance scientists like Leonardo Da Vinci, Galileo Galilei and Gerolamo Cardano have been considered as the most recognizable polymaths.
During the Renaissance, Italians made substantial contributions in science. Leonardo Da Vinci made significant discoveries in anatomy; the Father of modern Science,Galileo Galilei, made key improvements on the thermometer and telescope which allowed him to observe and describe the solar system. Descartes was not only a pioneer of analytic geometry but formulated a theory of mechanics and advanced ideas about the origins of animal movement and perception. Vision interested the physicists Young and Helmholtz, who studied optics and music. Newton extended Descartes' mathematics by inventing calculus, he investigated light and optics. Fourier founded a new branch of mathematics — infinite, periodic series — studied heat flow and infrared radiation, discovered the greenhouse effect. Girolamo Cardano, Blaise Pascal Pierre de Fermat, Von Neumann, Khinchin and Wiener, all mathematicians, made major contributions to science and probability theory, including the ideas behind computers, some of the foundations of statistical mechanics and quantum mechanics.
Many mathematically inclined scientists, including Galileo, were musicians. There are many compelling stories in medicine and biology, such as the development of ideas about the circulation of blood from Galen to Harvey. During the age of Enlightenment, Luigi Galvani, the pioneer of the bioelectromagnetics, discovered the animal electricity, he discovered that a charge applied to the spinal cord of a frog could generate muscular spasms throughout its body. Charges could make frog legs jump if the legs were no longer attached to a frog. While cutting a frog leg, Galvani's steel scalpel touched a brass hook, holding the leg in place; the leg twitched. Further experiments confirmed this effect, Galvani was convinced that he was seeing the effects of what he called animal electricity, the life force within the muscles of the frog. At the University of Pavia, Galvani's colleague Alessandro Volta was able to reproduce the results, but was sceptical o
A pollinator is an animal that moves pollen from the male anther of a flower to the female stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains. Insect pollinators include bees,. Vertebrates bats and birds, but some non-bat mammals and some lizards pollinate certain plants. Among the pollinating birds are hummingbirds and sunbirds with long beaks. Humans may carry out artificial pollination. A pollinator is different from a pollenizer, a plant, a source of pollen for the pollination process. Plants fall into pollination syndromes; these are characteristics such as: overall flower size, the depth and width of the corolla, the color, the scent, amount of nectar, composition of nectar, etc. For example, birds visit red flowers with long, narrow tubes and lots of nectar, but are not as attracted to wide flowers with little nectar and copious pollen, which are more attractive to beetles; when these characteristics are experimentally modified, pollinator visitation may decline.
It has been discovered that cycads, which are not flowering plants, are pollinated by insects. The most recognized pollinators are the various species of bees, which are plainly adapted to pollination. Bees are fuzzy and carry an electrostatic charge. Both features help pollen grains adhere to their bodies, but they have specialized pollen-carrying structures. Honey bees and their relatives do not have a scopa, but the hind leg is modified into a structure called the corbicula. Most bees gather nectar, a concentrated energy source, pollen, high protein food, to nurture their young, inadvertently transfer some among the flowers as they are working. Euglossine bees pollinate orchids, but these are male bees collecting floral scents rather than females gathering nectar or pollen. Female orchid bees act of flowers other than orchids. Eusocial bees such as honey bees need an steady pollen source to multiply. Honey bees travel from flower to flower, collecting nectar, pollen grains; the bee collects the pollen by rubbing against the anthers.
The pollen collects on the hind legs, in a structure referred to as a "pollen basket". As the bee flies from flower to flower, some of the pollen grains are transferred onto the stigma of other flowers. Nectar provides the energy for bee nutrition; when bees are rearing large quantities of brood, bees deliberately gather pollen to meet the nutritional needs of the brood. Good pollination management seeks to have bees in a "building" state during the bloom period of the crop, thus requiring them to gather pollen, making them more efficient pollinators. Thus, the management techniques of a beekeeper providing pollination services are different from, to some extent in tension with, those of a beekeeper, trying to produce honey. Millions of hives of honey bees are contracted out as pollinators by beekeepers, honey bees are by far the most important commercial pollinating agents, but many other kinds of pollinators, from blue bottle flies, to bumblebees, orchard mason bees, leaf cutter bees are cultured and sold for managed pollination.
Other species of bees differ in various details of their behavior and pollen-gathering habits, honey bees are not native to the Western Hemisphere. Many insects other than bees accomplish pollination by visiting flowers for nectar or pollen, or both. Many do so adventitiously, but the most important pollinators are specialists for at least parts of their lifecycles for at least certain functions. For example, males of many species of Hymenoptera, including many hunting wasps, rely on flowering plants as sources of energy and as territories for meeting fertile females that visit the flowers. Prominent examples are predatory wasps; the term "pollen wasps", in particular, is applied to the Masarinae, a subfamily of the Vespidae. Many bee flies, some Tabanidae and Nemestrinidae are adapted to pollinating fynbos and Karoo plants with narrow, deep corolla tubes, such as Lapeirousia species. Part of the adaptation takes the form of remarkably long probosces. Lepidoptera pollinate plants to various degrees.
They are not major pollinators of food crops, but various moths are important pollinators of other commercial crops such as tobacco. Pollination by certain moths may be important, however, or crucial, for some wildflowers mutually adapted to specialist pollinators. Spectacular examples include orchids such as Angraecum sesquipedale, dependant on a particular hawk moth, Morgan's sphinx. Yucca species provide other examples, bei
Portland is the largest and most populous city in the U. S. state of Oregon and the seat of Multnomah County. It is a major port in the Willamette Valley region of the Pacific Northwest, at the confluence of the Willamette and Columbia rivers; as of 2017, Portland had an estimated population of 647,805, making it the 26th-largest city in the United States, the second-most populous in the Pacific Northwest. 2.4 million people live in the Portland metropolitan statistical area, making it the 25th most populous MSA in the United States. Its Combined Statistical Area ranks 18th-largest with a population of around 3.2 million. 60% of Oregon's population resides within the Portland metropolitan area. Named after Portland, the Oregon settlement began to be populated in the 1830s near the end of the Oregon Trail, its water access provided convenient transportation of goods, the timber industry was a major force in the city's early economy. At the turn of the 20th century, the city had a reputation as one of the most dangerous port cities in the world, a hub for organized crime and racketeering.
After the city's economy experienced an industrial boom during World War II, its hard-edged reputation began to dissipate. Beginning in the 1960s, Portland became noted for its growing progressive political values, earning it a reputation as a bastion of counterculture; the city operates with a commission-based government guided by a mayor and four commissioners as well as Metro, the only directly elected metropolitan planning organization in the United States. The city government is notable for its land-use investment in public transportation. Portland is recognized as one of the world's most environmentally conscious cities because of its high walkability, large community of bicyclists, farm-to-table dining, expansive network of public transportation options, over 10,000 acres of public parks, its climate is marked by cool, rainy winters. This climate is ideal for growing roses, Portland has been called the "City of Roses" for over a century. During the prehistoric period, the land that would become Portland was flooded after the collapse of glacial dams from Lake Missoula, in what would become Montana.
These massive floods occurred during the last ice age and filled the Willamette Valley with 300 to 400 feet of water. Before American pioneers began arriving in the 1800s, the land was inhabited for many centuries by two bands of indigenous Chinook people—the Multnomah and the Clackamas; the Chinook people occupying the land were first documented in 1805 by Meriwether Lewis and William Clark. Before its European settlement, the Portland Basin of the lower Columbia River and Willamette River valleys had been one of the most densely populated regions on the Pacific Coast. Large numbers of pioneer settlers began arriving in the Willamette Valley in the 1830s via the Oregon Trail, though life was centered in nearby Oregon City. In the early 1840s a new settlement emerged ten miles from the mouth of the Willamette River halfway between Oregon City and Fort Vancouver; this community was referred to as "Stumptown" and "The Clearing" because of the many trees cut down to allow for its growth. In 1843 William Overton saw potential in the new settlement but lacked the funds to file an official land claim.
For 25 cents, Overton agreed to share half of the 640-acre site with Asa Lovejoy of Boston. In 1845 Overton sold his remaining half of the claim to Francis W. Pettygrove of Maine. Both Pettygrove and Lovejoy wished to rename "The Clearing" after their respective hometowns; this controversy was settled with a coin toss that Pettygrove won in a series of two out of three tosses, thereby providing Portland with its namesake. The coin used for this decision, now known as the Portland Penny, is on display in the headquarters of the Oregon Historical Society. At the time of its incorporation on February 8, 1851, Portland had over 800 inhabitants, a steam sawmill, a log cabin hotel, a newspaper, the Weekly Oregonian. A major fire swept through downtown in August 1873, destroying twenty blocks on the west side of the Willamette along Yamhill and Morrison Streets, causing $1.3 million in damage. By 1879, the population had grown to 17,500 and by 1890 it had grown to 46,385. In 1888, the city built the first steel bridge built on the West Coast.
Portland's access to the Pacific Ocean via the Willamette and Columbia rivers, as well as its easy access to the agricultural Tualatin Valley via the "Great Plank Road", provided the pioneer city with an advantage over other nearby ports, it grew quickly. Portland remained the major port in the Pacific Northwest for much of the 19th century, until the 1890s, when Seattle's deepwater harbor was connected to the rest of the mainland by rail, affording an inland route without the treacherous navigation of the Columbia River; the city had its own Japantown, for one, the lumber industry became a prominent economic presence, due to the area's large population of Douglas Firs, Western Hemlocks, Red Cedars, Big Leaf Maple trees. Portland developed a reputation early in its history as a gritty port town; some historians have described the city's early establishment as being a "scion of New England. In 1889, The Oregonian called Portland "the most filthy city in the Northern States", due to the unsanitary sewers and gutters, and, at the turn of the 20th century, it was considered one of the most dangerous port cities in the world.
The city housed a large number of saloons
Butterflies are insects in the macrolepidopteran clade Rhopalocera from the order Lepidoptera, which includes moths. Adult butterflies have large brightly coloured wings, conspicuous, fluttering flight; the group comprises the large superfamily Papilionoidea, which contains at least one former group, the skippers, the most recent analyses suggest it contains the moth-butterflies. Butterfly fossils date to the Paleocene, about 56 million years ago. Butterflies have the typical four-stage insect life cycle. Winged adults lay eggs on the food plant; the caterpillars grow, sometimes rapidly, when developed, pupate in a chrysalis. When metamorphosis is complete, the pupal skin splits, the adult insect climbs out, after its wings have expanded and dried, it flies off; some butterflies in the tropics, have several generations in a year, while others have a single generation, a few in cold locations may take several years to pass through their entire life cycle. Butterflies are polymorphic, many species make use of camouflage and aposematism to evade their predators.
Some, like the monarch and the painted lady, migrate over long distances. Many butterflies are attacked by parasites or parasitoids, including wasps, protozoans and other invertebrates, or are preyed upon by other organisms; some species are pests because in their larval stages they can damage domestic trees. Larvae of a few butterflies eat harmful insects, a few are predators of ants, while others live as mutualists in association with ants. Culturally, butterflies are a popular motif in the literary arts; the Oxford English Dictionary derives the word straightforwardly from Old English butorflēoge, butter-fly. A possible source of the name is the bright yellow male of the brimstone; the earliest Lepidoptera fossils are of a small moth, Archaeolepis mane, of Jurassic age, around 190 million years ago. Butterflies evolved from moths, so while the butterflies are monophyletic, the moths are not; the oldest butterflies are from the Palaeocene MoClay or Fur Formation of Denmark 55 million years old.
The oldest American butterfly is the Late Eocene Prodryas persephone from the Florissant Fossil Beds 34 million years old. Traditionally, the butterflies have been divided into the superfamily Papilionoidea excluding the smaller groups of the Hesperiidae and the more moth-like Hedylidae of America. Phylogenetic analysis suggests that the traditional Papilionoidea is paraphyletic with respect to the other two groups, so they should both be included within Papilionoidea, to form a single butterfly group, thereby synonymous with the clade Rhopalocera. Butterfly adults are characterized by their four scale-covered wings, which give the Lepidoptera their name; these scales give butterfly wings their colour: they are pigmented with melanins that give them blacks and browns, as well as uric acid derivatives and flavones that give them yellows, but many of the blues, greens and iridescent colours are created by structural coloration produced by the micro-structures of the scales and hairs. As in all insects, the body is divided into three sections: the head and abdomen.
The thorax is composed of each with a pair of legs. In most families of butterfly the antennae are clubbed, unlike those of moths which may be threadlike or feathery; the long proboscis can be coiled. Nearly all butterflies are diurnal, have bright colours, hold their wings vertically above their bodies when at rest, unlike the majority of moths which fly by night, are cryptically coloured, either hold their wings flat or fold them over their bodies; some day-flying moths, such as the hummingbird hawk-moth, are exceptions to these rules. Butterfly larvae, have a hard head with strong mandibles used for cutting their food, most leaves, they have cylindrical bodies, with ten segments to the abdomen with short prolegs on segments 3–6 and 10. Many are well camouflaged; the pupa or chrysalis, unlike that of moths, is not wrapped in a cocoon. Many butterflies are sexually dimorphic. Most butterflies have the ZW sex-determination system where females are the heterogametic sex and males homogametic. Butterflies are distributed worldwide except Antarctica.
Of these, 775 are Nearctic. The monarch butterfly is native to the Americas, but in the nineteenth century or before, spread across the world, is now found in Australia, New Zealand, other parts of Oceania, the Iberian Peninsula, it is not clear.
A teacher is a person who helps others to acquire knowledge, competences or values. Informally the role of teacher may be taken on by anyone. In some countries, teaching young people of school age may be carried out in an informal setting, such as within the family, rather than in a formal setting such as a school or college; some other professions may involve a significant amount of teaching. In most countries, formal teaching of students is carried out by paid professional teachers; this article focuses on those who are employed, as their main role, to teach others in a formal education context, such as at a school or other place of initial formal education or training. A teacher's role may vary among cultures. Teachers may provide instruction in literacy and numeracy, craftsmanship or vocational training, the arts, civics, community roles, or life skills. Formal teaching tasks include preparing lessons according to agreed curricula, giving lessons, assessing pupil progress. A teacher's professional duties may extend beyond formal teaching.
Outside of the classroom teachers may accompany students on field trips, supervise study halls, help with the organization of school functions, serve as supervisors for extracurricular activities. In some education systems, teachers may have responsibility for student discipline. Teaching is a complex activity; this is in part because teaching is a social practice, that takes place in a specific context and therefore reflects the values of that specific context. Factors that influence what is expected of teachers include history and tradition, social views about the purpose of education, accepted theories about learning, etc; the competencies required by a teacher are affected by the different ways in which the role is understood around the world. Broadly, there seem to be four models: the teacher as manager of instruction; the OECD has argued that it is necessary to develop a shared definition of the skills and knowledge required by teachers, in order to guide teachers' career-long education and professional development.
Some evidence-based international discussions have tried to reach such a common understanding. For example, the European Union has identified three broad areas of competences that teachers require: Working with others Working with knowledge and information, Working in and with society. Scholarly consensus is emerging that what is required of teachers can be grouped under three headings: knowledge craft skills and dispositions, it has been found that teachers who showed enthusiasm towards the course materials and students can create a positive learning experience. These teachers do not teach by rote but attempt to find new invigoration for the course materials on a daily basis. One of the challenges facing teachers is that they may have covered a curriculum until they begin to feel bored with the subject, their attitude may in turn bore the students. Students who had enthusiastic teachers tend to rate them higher than teachers who didn't show much enthusiasm for the course materials. Teachers that exhibit enthusiasm can lead to students who are more to be engaged, interested and curious about learning the subject matter.
Recent research has found a correlation between teacher enthusiasm and students' intrinsic motivation to learn and vitality in the classroom. Controlled, experimental studies exploring intrinsic motivation of college students has shown that nonverbal expressions of enthusiasm, such as demonstrative gesturing, dramatic movements which are varied, emotional facial expressions, result in college students reporting higher levels of intrinsic motivation to learn, but while a teacher's enthusiasm has been shown to improve motivation and increase task engagement, it does not improve learning outcomes or memory for the material. There are various mechanisms by which teacher enthusiasm may facilitate higher levels of intrinsic motivation. Teacher enthusiasm may contribute to a classroom atmosphere of energy and enthusiasm which feeds student interest and excitement in learning the subject matter. Enthusiastic teachers may lead to students becoming more self-determined in their own learning process; the concept of mere exposure indicates that the teacher's enthusiasm may contribute to the student's expectations about intrinsic motivation in the context of learning.
Enthusiasm may act as a "motivational embellishment", increasing a student's interest by the variety and surprise of the enthusiastic teacher's presentation of the material. The concept of emotional contagion, may apply. Research shows that student motivation and attitudes towards school are linked to student-teacher relationships. Enthusiastic teachers are good at creating beneficial relations with their students, their ability to create effective learning environments that foster student achievement depends on the kind of relationship they build with their students. Useful teacher-to-studen
Field Museum of Natural History
The Field Museum of Natural History known as The Field Museum, is a natural history museum in Chicago, is one of the largest such museums in the world. The museum maintains its status as a premier natural-history museum through the size and quality of its educational and scientific programs, as well as due to its extensive scientific-specimen and artifact collections; the diverse, high-quality permanent exhibitions, which attract up to two million visitors annually, range from the earliest fossils to past and current cultures from around the world to interactive programming demonstrating today's urgent conservation needs. The museum is named in honor of its first major benefactor, the department-store magnate Marshall Field; the museum and its collections originated from the 1893 World’s Columbian Exposition and the artifacts displayed at the fair. The museum maintains a temporary exhibition program of traveling shows as well as in-house produced topical exhibitions; the professional staff maintains collections of over 24 million specimens and objects that provide the basis for the museum’s scientific-research programs.
These collections include the full range of existing biodiversity, meteorites and rich anthropological collections and cultural artifacts from around the globe. The museum's library, which contains over 275,000 books and photo archives focused on biological systematics, evolutionary biology, archaeology and material culture, supports the museum’s academic-research faculty and exhibit development; the academic faculty and scientific staff engage in field expeditions, in biodiversity and cultural research on every continent, in local and foreign student training, in stewardship of the rich specimen and artifact collections. They work in close collaboration with public programming exhibitions and education initiatives; the Field Museum and its collections originated from the 1893 World’s Columbian Exposition and the artifacts displayed at the fair. In order to house for future generations the exhibits and collections assembled for the Exposition, Edward Ayer convinced the merchant Marshall Field to fund the establishment of a museum.
Titled the Columbian Museum of Chicago in honor of its origins, the Field Museum was incorporated by the State of Illinois on September 16, 1893, for the purpose of the "accumulation and dissemination of knowledge, the preservation and exhibition of artifacts illustrating art, archaeology and history." The Columbian Museum of Chicago occupied the only building remaining from the World's Columbian Exposition in Jackson Park, the Palace of Fine Arts. It is now home to the Chicago Museum of Industry. In 1905, the museum's name was changed to the Field Museum of Natural History to honor its first major benefactor and to reflect its focus on the natural sciences. During the period from 1943 to 1966, the museum was known as the Chicago Natural History Museum. In 1921, the Museum moved from its original location in Jackson Park to its present site on Chicago Park District property near downtown. By the late 1930s the Field had emerged as one of the three premier museums in the United States, the other two being the American Museum of Natural History in New York and the National Museum of Natural History at the Smithsonian Institution in Washington DC.
The museum has maintained its reputation through continuous growth, expanding the scope of collections and its scientific research output, in addition to the its award-winning exhibitions, outreach publications, programs. The Field Museum is part of Chicago’s lakefront Museum Campus that includes the John G. Shedd Aquarium and the Adler Planetarium. In 2015, it was reported that an employee had defrauded the museum of $900,000 over a seven-year period to 2014. Animal exhibitions and dioramas such as Nature Walk, Mammals of Asia, Mammals of Africa that allow visitors an up-close look at the diverse habitats that animals inhabit. Most notably featured are the infamous man-eating lions of Tsavo. Evolving Planet follows the evolution of life on Earth over 4 billion years; the exhibit showcases fossils of single-celled organisms, Permian synapsids, extinct mammals, early hominoids. The Field Museum's non-mammalian synapsid collection consists of over 1100 catalogued specimens, including 46 holotypes.
The collection of basal synapsids includes 29 holotypes of caseid, edaphosaurid and sphenacodontid species - 88% of catalogued specimens. Inside Ancient Egypt offers a glimpse into. Twenty-three human mummies are on display as well as many mummified animals; the exhibit features a three-story replica of the mastaba tomb of the son of Unas. Displayed are: an ancient marketplace showing artifacts of everyday life, a shrine to the cat goddess Bastet, dioramas showing the afterlife preparation process for the dead; the Ancient Americas displays 13,000 years of human ingenuity and achievement in the Western Hemisphere, where hundreds of diverse societies thrived long before the arrival of Europeans. In this large permanent exhibition visitors can learn the epic story of the peopling of these continents, from the Arctic to the tip of South America. Cultural exhibitions include sections on Tibet and China, where visitors can view traditional clothing. There is an exhibit on life in Africa, where visitors can learn about the many different cultures on the continent, an exhibit where visitors may "visit" several Pacific Islands.
The museum houses an authentic 19th century Māori Meeting House, Ruatepupuke II, from Tokomaru Bay, New Zealand. The Grainger Hall of Gems and its large collection o
Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of invertebrates include arthropods, mollusks and cnidarians; the majority of animal species are invertebrates. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata; some of the so-called invertebrates, such as the Tunicata and Cephalochordata are more related to the vertebrates than to other invertebrates. This makes the invertebrates paraphyletic, so the term has little meaning in taxonomy; the word "invertebrate" comes from the Latin word vertebra, which means a joint in general, sometimes a joint from the spinal column of a vertebrate. The jointed aspect of vertebra is derived from the concept of turning, expressed in the root verto or vorto, to turn; the prefix in- means "not" or "without". The term invertebrates is not always precise among non-biologists since it does not describe a taxon in the same way that Arthropoda, Vertebrata or Manidae do.
Each of these terms describes a valid taxon, subphylum or family. "Invertebrata" is a term of convenience, not a taxon. The Vertebrata as a subphylum comprises such a small proportion of the Metazoa that to speak of the kingdom Animalia in terms of "Vertebrata" and "Invertebrata" has limited practicality. In the more formal taxonomy of Animalia other attributes that logically should precede the presence or absence of the vertebral column in constructing a cladogram, for example, the presence of a notochord; that would at least circumscribe the Chordata. However the notochord would be a less fundamental criterion than aspects of embryological development and symmetry or bauplan. Despite this, the concept of invertebrates as a taxon of animals has persisted for over a century among the laity, within the zoological community and in its literature it remains in use as a term of convenience for animals that are not members of the Vertebrata; the following text reflects earlier scientific understanding of the term and of those animals which have constituted it.
According to this understanding, invertebrates do not possess a skeleton of bone, either internal or external. They include hugely varied body plans. Many have like jellyfish or worms. Others have outer shells like those of insects and crustaceans; the most familiar invertebrates include the Protozoa, Coelenterata, Nematoda, Echinodermata and Arthropoda. Arthropoda include insects and arachnids. By far the largest number of described invertebrate species are insects; the following table lists the number of described extant species for major invertebrate groups as estimated in the IUCN Red List of Threatened Species, 2014.3. The IUCN estimates that 66,178 extant vertebrate species have been described, which means that over 95% of the described animal species in the world are invertebrates; the trait, common to all invertebrates is the absence of a vertebral column: this creates a distinction between invertebrates and vertebrates. The distinction is one of convenience only. Being animals, invertebrates are heterotrophs, require sustenance in the form of the consumption of other organisms.
With a few exceptions, such as the Porifera, invertebrates have bodies composed of differentiated tissues. There is typically a digestive chamber with one or two openings to the exterior; the body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical. A minority, exhibit no symmetry. One example of asymmetric invertebrates includes all gastropod species; this is seen in snails and sea snails, which have helical shells. Slugs appear externally symmetrical. Other gastropods develop external asymmetry, such as Glaucus atlanticus that develops asymmetrical cerata as they mature; the origin of gastropod asymmetry is a subject of scientific debate. Other examples of asymmetry are found in hermit crabs, they have one claw much larger than the other. If a male fiddler loses its large claw, it will grow another on the opposite side after moulting. Sessile animals such as sponges are asymmetrical alongside coral colonies. Neurons differ in invertebrates from mammalian cells.
Invertebrates cells fire in response to similar stimuli as mammals, such as tissue trauma, high temperature, or changes in pH. The first invertebrate in which a neuron cell was identified was the medicinal leech, Hirudo medicinalis. Learning and memory using nociceptors in the sea hare, Aplysia has been described. Mollusk neurons are able to detect tissue trauma. Neurons have been identified in a wide range of invertebrate species, including annelids, molluscs and arthropods. One type of invertebrate respi