1.
Meerkat
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The meerkat or suricate is a small carnivoran belonging to the mongoose family. It is the member of the genus Suricata. Meerkats live in all parts of the Kalahari Desert in Botswana, in much of the Namib Desert in Namibia and southwestern Angola, a group of meerkats is called a mob, gang or clan. A meerkat clan often contains about 20 meerkats, but some super-families have 50 or more members, in captivity, meerkats have an average life span of 12–14 years, and about half this in the wild. Meerkat is a loanword from Afrikaans, the name has a Dutch origin, but by misidentification. In Dutch, meerkat means the guenon, a monkey of the Cercopithecus genus, the meerkat is a small diurnal herpestid weighing on average about 0.5 to 2.5 kilograms. Its long slender body and limbs give it a length of 35 to 50 centimetres. The meerkat uses its tail to balance when standing upright, as well as for signaling and its face tapers, coming to a point at the nose, which is brown. The eyes always have black patches around them, and they have small black crescent-shaped ears, like cats, meerkats have binocular vision, their eyes being on the front of their faces. At the end of each of a meerkats fingers is a used for digging burrows. Claws are also used with muscular hindlegs to help climb trees, Meerkats have four toes on each foot and long slender limbs. The coat is usually peppered gray, tan, or brown with silver and they have short parallel stripes across their backs, extending from the base of the tail to the shoulders. The patterns of stripes are unique to each meerkat, the underside of the meerkat has no markings, but the belly has a patch which is only sparsely covered with hair and shows the black skin underneath. The meerkat uses this area to heat while standing on its rear legs. Meerkats are primarily insectivores, but also eat animals, plants. Meerkats are immune to certain types of venom, including the very strong venom of the scorpions of the Kalahari Desert. Baby meerkats do not start foraging for food until they are about 1 month old, Meerkats forage in a group with one sentry on guard watching for predators while the others search for food. Sentry duty is usually approximately an hour long, the meerkat standing guard makes peeping sounds when all is well
2.
Anatomical terminology
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Anatomical terminology is a form of scientific terminology used by anatomists, zoologists, and health professionals such as doctors. Anatomical terminology uses many terms, suffixes, and prefixes deriving from Ancient Greek. These terms can be confusing to those unfamiliar with them, but can be more precise reducing ambiguity, also, since these anatomical terms are not used in everyday conversation, their meanings are less likely to change, and less likely to be misinterpreted. By using precise anatomical terminology such ambiguity is eliminated, an international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the prefixes and suffixes are used to add meanings to different roots. The root of a term refers to an organ, tissue. For example, in the disorder hypertension, the prefix hyper- means high or over, the roots, prefixes and suffixes are often derived from Greek or Latin, and often quite dissimilar from their English-language variants. Latin names of such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for two-headed. The first word tells us what we are speaking about, the second describes it, when describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near. These landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, the cephalon or cephalic region refers to the head. This area is differentiated into the cranium, facies, frons, oculus, auris, bucca, nausus, oris. The neck area is called the cervicis or cervical region, examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body, for example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, similarly, in the arms, different terminology is often used in the arms, in part to reduce ambiguity as what is the front, back, inner and outer surfaces. For this reason, the terms below are used, Radial referring to the radius bone, ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet. International morphological terminology is used by the colleges of medicine and dentistry and it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research, teaching and medical care. The international morphological terminology refers to morphological sciences as a biological sciences branch, in this field, the form and structure are examined as well as the changes or developments in the organism
3.
Organism
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In biology, an organism is any contiguous living system, such as an animal, plant, fungus, protist, archaeon, or bacterium. All known types of organisms are capable of some degree of response to stimuli, reproduction, growth and development and homeostasis. An organism consists of one or more cells, when it has one cell it is known as an organism. Most unicellular organisms are of microscopic scale and are thus described as microorganisms. Humans are multicellular organisms composed of trillions of cells grouped into specialized tissues. An organism may be either a prokaryote or a eukaryote, prokaryotes are represented by two separate domains—bacteria and archaea. Eukaryotic organisms are characterized by the presence of a cell nucleus. Fungi, animals and plants are examples of kingdoms of organisms within the eukaryotes, estimates on the number of Earths current species range from 10 million to 14 million, of which only about 1.2 million have been documented. More than 99% of all species, amounting to five billion species. In 2016, a set of 355 genes from the last universal ancestor of all living organisms living was identified. The term organism first appeared in the English language in 1703 and it is directly related to the term organization. There is a tradition of defining organisms as self-organizing beings. An organism may be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life. Dictionary definitions can be broad, using such as any living structure, such as a plant, animal, fungus or bacterium, capable of growth. Many definitions exclude viruses and possible man-made non-organic life forms, as viruses are dependent on the machinery of a host cell for reproduction. A superorganism is an organism consisting of individuals working together as a single functional or social unit. There has been controversy about the best way to define the organism, several contributions are responses to the suggestion that the category of organism may well not be adequate in biology. Viruses are not typically considered to be organisms because they are incapable of autonomous reproduction and this controversy is problematic because some cellular organisms are also incapable of independent survival and live as obligatory intracellular parasites
4.
Eye
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Eyes are organs of the visual system. They provide organisms vision, the ability to process visual detail, eyes detect light and convert it into electro-chemical impulses in neurons. Eyes with resolving power have come in ten different forms. Image-resolving eyes are present in molluscs, chordates and arthropods, the simplest eyes, such as those in microorganisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. Complex eyes can distinguish shapes and colours, the visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception. In other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses, the first proto-eyes evolved among animals 600 million years ago about the time of the Cambrian explosion. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, in most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells and the rod cells in the retina detect, the visual signals are then transmitted to the brain via the optic nerve. The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing vision is achieved by telescoping the lens—similar to how a camera focuses. Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, each sensor has its own lens and photosensitive cell. Some eyes have up to 28,000 such sensors, which are arranged hexagonally, compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have eyes of only a few facets, each with a retina capable of creating an image. With each eye viewing a different thing, an image from all the eyes is produced in the brain, providing very different. Possessing detailed hyperspectral colour vision, the Mantis shrimp has been reported to have the worlds most complex colour vision system, trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes, in this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however, some trilobites had only one, in contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a pair of simple eyes with a narrow field of view. Some insect larvae, like caterpillars, have a different type of simple eye which gives a rough image, some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot actually see in the normal sense
5.
Nose
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Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses, behind the nasal cavity, air next passes through the pharynx, shared with the digestive system, and then into the rest of the respiratory system. In humans, the nose is located centrally on the face, on most other mammals, it is located on the upper tip of the snout. Capillary structures of the warm and humidify air entering the body, later. During exhalation, the capillaries then aid recovery of some moisture, mostly as a function of thermal regulation, the wet nose of dogs is useful for the perception of direction. The sensitive cold receptors in the skin detect the place where the nose is cooled the most, in amphibians and lungfish, the nostrils open into small sacs that, in turn, open into the forward roof of the mouth through the choanae. These sacs contain an amount of olfactory epithelium, which, in the case of caecilians. Despite the general similarity in structure to those of amphibians, the nostrils of lungfish are not used in respiration, in reptiles, the nasal chamber is generally larger, with the choanae located much further back in the roof of the mouth. In crocodilians, the chamber is long, helping the animal to breathe while partially submerged. The reptilian nasal chamber is divided into three parts, a vestibule, the main olfactory chamber, and a posterior nasopharynx. The olfactory chamber is lined by olfactory epithelium on its upper surface, the vomeronasal organ is well-developed in lizards and snakes, in which it no longer connects with the nasal cavity, opening directly into the roof of the mouth. It is smaller in turtles, in which it retains its original nasal connection, birds have a similar nose to reptiles, with the nostrils located at the upper rear part of the beak. Since they generally have a sense of smell, the olfactory chamber is small. In many birds, including doves and fowls, the nostrils are covered by a protective shield. The vomeronasal organ of birds is either under-developed or altogether absent, the nasal cavities in mammals are both fused into one. Among most species they are large, typically occupying up to half the length of the skull. In some groups, however, including primates, bats, and cetaceans, the nose has been reduced. The enlarged nasal cavity contains complex turbinates forming coiled scroll-like shapes that help to warm the air before it reaches the lungs, the cavity also extends into neighbouring skull bones, forming additional air cavities known as paranasal sinuses
6.
Mouth
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It is also the cavity lying at the upper end of the alimentary canal, bounded on the outside by the lips and inside by the pharynx and containing in higher vertebrates the tongue and teeth. This cavity is known as the buccal cavity, from the Latin bucca. Some animal phyla, including vertebrates, have a digestive system, with a mouth at one end. Which end forms first in ontogeny is a used to classify animals into protostome and deuterostome. In the first multicellular animals there was probably no mouth or gut, the particles became enclosed in vacuoles into which enzymes were secreted and digestion took place intracellularly. The digestive products were absorbed into the cytoplasm and diffused into other cells, the vast majority of other multicellular organisms have a mouth and a gut, the lining of which is continuous with the epithelial cells on the surface of the body. A few animals which live parasitically originally had guts but have secondarily lost these structures, the original gut of multicellular organisms probably consisted of a simple sac with a single opening, the mouth. Indigestible waste is ejected through the mouth, in animals at least as complex as an earthworm, the embryo forms a dent on one side, the blastopore, which deepens to become the archenteron, the first phase in the formation of the gut. In deuterostomes, the blastopore becomes the anus while the gut tunnels through to make another opening. In the protostomes, it used to be thought that the formed the mouth while the anus formed later as an opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the slit-like blastopore close up in the middle, apart from sponges and placozoans, almost all animals have an internal gut cavity which is lined with gastrodermal cells. In less advanced invertebrates such as the sea anemone, the mouth also acts as an anus, circular muscles around the mouth are able to relax or contract in order to open or close it. A fringe of tentacles thrusts food into the cavity and it can gape widely enough to large prey items. Food passes first into a pharynx and digestion occurs extracellularly in the gastrovascular cavity, annelids have simple tube-like gets and the possession of an anus allows them to separate the digestion of their foodstuffs from the absorption of the nutrients. Many molluscs have a radula which is used to scrape microscopic particles off surfaces, in invertebrates with hard exoskeletons, various mouthparts may be involved in feeding behaviour. Insects have a range of mouthparts suited to their mode of feeding and these include mandibles, maxillae and labium and can be modified into suitable appendages for chewing, cutting, piercing, sponging and sucking. Decapods have six pairs of appendages, one pair of mandibles. Sea urchins have a set of five sharp calcareous plates which are used as jaws and are known as Aristotles lantern, in vertebrates, the first part of the digestive system is the buccal cavity, commonly known as the mouth
7.
Visual perception
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Visual perception is the ability to interpret the surrounding environment using light in the visible spectrum reflected by the objects in the environment. The resulting perception is known as visual perception, eyesight, sight. The visual system in animals allows individuals to assimilate information from their surroundings, the act of seeing starts when the cornea and then the lens of the eye focuses light from its surroundings onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of light into neuronal signals. These signals are processed via complex feedforward and feedback processes by different parts of the brain, signals from the retina can also travel directly from the retina to the superior colliculus. The perception of objects and the totality of the scene is accomplished by the visual association cortex. The visual association cortex combines all sensory information perceived by the cortex which contains thousands of modules that are part of modular neural networks. The neurons in the cortex send axons to the extrastriate cortex. The major problem in perception is that what people see is not simply a translation of retinal stimuli. Thus people interested in perception have long struggled to explain what visual processing does to create what is actually seen, there were two major ancient Greek schools, providing a primitive explanation of how vision is carried out in the body. The first was the theory which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. If an object was seen directly it was by means of coming out of the eyes. This theory was championed by scholars like Euclid and Ptolemy and their followers, the second school advocated the so-called intro-mission approach which sees vision as coming from something entering the eyes representative of the object. Plato makes this assertion in his dialogue Timaeus, as does Aristotle, alhazen carried out many investigations and experiments on visual perception, extended the work of Ptolemy on binocular vision, and commented on the anatomical works of Galen. Leonardo da Vinci is believed to be the first to recognize the special qualities of the eye. He wrote The function of the human eye, was described by a large number of authors in a certain way. But I found it to be completely different and his main experimental finding was that there is only a distinct and clear vision at the line of sight—the optical line that ends at the fovea. Although he did not use these words literally he actually is the father of the distinction between foveal and peripheral vision
8.
Hearing
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Hearing, or auditory perception, is the ability to perceive sound by detecting vibrations, changes in the pressure of the surrounding medium through time, through an organ such as the ear. Sound may be heard through solid, liquid, or gaseous matter and it is one of the traditional five senses, partial or total inability to hear is called hearing loss. Like touch, audition requires sensitivity to the movement of molecules in the world outside the organism, both hearing and touch are types of mechanosensation. There are three components of the human ear, the outer ear, the middle ear. The outer ear includes the pinna, the part of the ear, as well as the ear canal which terminates at the eardrum. The pinna serves to focus sound waves through the ear canal toward the eardrum, because of the asymmetrical character of the outer ear of most mammals, sound is filtered differently on its way into the ear depending on what vertical location it is coming from. This gives these animals the ability to localize sound vertically, the eardrum is an airtight membrane, and when sound waves arrive there, they cause it to vibrate following the waveform of the sound. The middle ear consists of a small air-filled chamber that is located medial to the eardrum, within this chamber are the three smallest bones in the body, known collectively as the ossicles which include the malleus, incus and stapes. They aid in the transmission of the vibrations from the eardrum to the inner ear, the purpose of the middle ear ossicles is to overcome the impedance mismatch between air and water, by providing impedance matching. Also located in the ear are the stapedius and tensor tympani muscles which protect the hearing mechanism through a stiffening reflex. The stapes transmits sound waves to the ear through the oval window. The round window, another flexible membrane, allows for the displacement of the inner ear fluid caused by the entering sound waves. The inner ear consists of the cochlea, which is a spiral-shaped, fluid-filled tube and it is divided lengthwise by the organ of Corti, which is the main organ of mechanical to neural transduction. Inside the organ of Corti is the membrane, a structure that vibrates when waves from the middle ear propagate through the cochlear fluid – endolymph. The basilar membrane is tonotopic, so that frequency has a characteristic place of resonance along it. Characteristic frequencies are high at the entrance to the cochlea. Basilar membrane motion causes depolarization of the cells, specialized auditory receptors located within the organ of Corti. While the hair cells do not produce action potentials themselves, they release neurotransmitter at synapses with the fibers of the auditory nerve, which does produce action potentials
9.
Olfaction
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Olfaction, also known as olfactics, is the sense of smell. This sense is mediated by specialized cells, called olfactory receptors. In humans, olfaction – the detection of smells – occurs when odorant molecules bind to sites on these receptors. These receptors come together at the glomerulus, a structure that transmits signals to the olfactory bulb, many vertebrates, including most mammals and reptiles, have two distinct olfactory systems—the main olfactory system, and the accessory olfactory system. For air-breathing animals, the olfactory system detects volatile chemicals. Olfaction, along with taste, is a form of chemoreception, the chemicals that activate the olfactory system, generally at very low concentrations, are called odorants. Although taste and smell are separate sensory systems in land animals, volatile small molecule odorants, non-volatile proteins, and non-volatile hydrocarbons may all produce olfactory sensations. Some animal species are able to smell carbon dioxide in minute concentrations, in vertebrates, smells are sensed by olfactory sensory neurons in the olfactory epithelium. The olfactory epithelium is made up of at least six morphologically and biochemically different cell types, the proportion of olfactory epithelium compared to respiratory epithelium gives an indication of the animals olfactory sensitivity. Humans have about 10 cm2 of olfactory epithelium, whereas some dogs have 170 cm2, a dogs olfactory epithelium is also considerably more densely innervated, with a hundred times more receptors per square centimeter. This may occur by diffusion or by the binding of the odorant to odorant-binding proteins, the mucus overlying the epithelium contains mucopolysaccharides, salts, enzymes, and antibodies. This mucus acts as a solvent for odor molecules, flows constantly, in insects, smells are sensed by olfactory sensory neurons in the chemosensory sensilla, which are present in insect antenna, palps, and tarsa, but also on other parts of the insect body. Odorants penetrate into the pores of chemosensory sensilla and get in contact with insect odorant-binding proteins or Chemosensory proteins. The binding of the ligand to the leads to an action potential in the receptor neuron, via a second messenger pathway. In mammals, the odorants stimulate adenylate cyclase to synthesize cAMP via a G protein called Golf, CAMP, which is the second messenger here, opens a cyclic nucleotide-gated ion channel, producing an influx of cations into the cell, slightly depolarising it. The Ca2+ in turn opens a Ca2+-activated chloride channel, leading to efflux of Cl−, further depolarizing the cell, Ca2+ is then extruded through a sodium-calcium exchanger. A calcium-calmodulin complex also acts to inhibit the binding of cAMP to the cAMP-dependent channel and this mechanism of transduction is somewhat unusual, in that cAMP works by directly binding to the ion channel rather than through activation of protein kinase A. There are also similarities in the immediate processing of stimuli by lateral inhibition
10.
Taste
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Taste, gustatory perception, or gustation is one of the five traditional senses that belongs to the gustatory system. Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on taste buds in the oral cavity, Taste, along with smell and trigeminal nerve stimulation, determines flavors of food or other substances. Humans have taste receptors on taste buds and other areas including the surface of the tongue. The tongue is covered with thousands of small bumps called papillae, within each papilla are hundreds of taste buds. The exception to this is the filiform papillae that do not contain taste buds, there are between 2000 and 5000 taste buds that are located on the back and front of the tongue. Others are located on the roof, sides and back of the mouth, each taste bud contains 50 to 100 taste receptor cells. The sensation of taste includes five established basic tastes, sweetness, sourness, saltiness, bitterness, scientific experiments have proven that these five tastes exist and are distinct from one another. Taste buds are able to differentiate among different tastes through detecting interaction with different molecules or ions, Sweet, umami, and bitter tastes are triggered by the binding of molecules to G protein-coupled receptors on the cell membranes of taste buds. Saltiness and sourness are perceived when alkali metal or hydrogen ions enter taste buds, temperature, detected by thermoreceptors, and coolness and hotness, through chemesthesis. As taste senses both harmful and beneficial things, all basic tastes are classified as either aversive or appetitive, Sweetness helps to identify energy-rich foods, while bitterness serves as a warning sign of poisons. Among humans, taste perception begins to fade around 50 years of age because of loss of tongue papillae, Taste in the gustatory system allows humans to distinguish between safe and harmful food, and to gauge foods’ nutritional value. Digestive enzymes in saliva begin to dissolve food into base chemicals that are washed over the papillae, the tongue is covered with thousands of small bumps called papillae, which are visible to the naked eye. Within each papilla are hundreds of taste buds, the exception to this are the filiform papillae that do not contain taste buds. There are between 2000 and 5000 taste buds that are located on the back and front of the tongue, others are located on the roof, sides and back of the mouth, and in the throat. Each taste bud contains 50 to 100 taste receptor cells, bitter foods are generally found unpleasant, while sour, salty, sweet, and meaty tasting foods generally provide a pleasurable sensation. The five specific tastes received by taste receptors are saltiness, sweetness, bitterness, sourness, and umami, as of the early twentieth century, physiologists and psychologists believed there were four basic tastes, sweetness, sourness, saltiness, and bitterness. At that time umami was not identified but now a number of authorities recognize it as the fifth taste. One study found that salt and sour taste mechanisms detect, in different ways, the presence of sodium chloride in the mouth, however
11.
Bilateria
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In contrast, radially symmetrical animals like jellyfish have a topside and a downside, but no identifiable front or back. The bilateria are a group of animals, including the majority of phyla but not sponges, cnidarians, placozoans. For the most part, bilateral embryos are triploblastic, having three germ layers, endoderm, mesoderm, and ectoderm. Nearly all are symmetrical, or approximately so, the most notable exception is the echinoderms, which achieve near-radial symmetry as adults. Except for a few phyla, bilaterians have complete digestive tracts with a separate mouth, some bilaterians lack body cavities, while others display primary body cavities or secondary cavities. The hypothetical most recent common ancestor of all bilateria is termed the Urbilaterian, the nature of the first bilaterian is a matter of debate. The first evidence of bilateria in the record comes from trace fossils in Ediacaran sediments. Earlier fossils are controversial, the fossil Vernanimalcula may be the earliest known bilaterian, fossil embryos are known from around the time of Vernanimalcula, but none of these have bilaterian affinities. Burrows believed to have created by bilaterian life forms have been found in the Tacuarí Formation of Uruguay. There are two main superphyla of Bilateria, the deuterostomes include the echinoderms, hemichordates, chordates, and a few smaller phyla. The protostomes include most of the rest, such as arthropods, annelids, mollusks, flatworms, there are a number of differences, most notably in how the embryo develops. In particular, the first opening of the embryo becomes the mouth in protostomes, many taxonomists now recognize at least two more superphyla among the protostomes, Ecdysozoa and Lophotrochozoa. Within the latter, some researchers also recognize another superphylum, Platyzoa, the arrow worms have proven particularly difficult to classify, with some taxonomists placing them among the deuterostomes and others placing them among the protostomes. The two most recent studies to address the question of chaetognath origins support protostome affinities, a modern consensus phylogeny for Bilateria is shown below, although the position of certain clades are still controversial and the tree has changed considerably between 2000 and 2010. Nodes marked with * have received broad consensus, a prominent alternative tree is championed by Nielsen. Embryological origins of the mouth and anus Tree of Life web project — Bilateria University of California Museum of Paleontology — Systematics of the Metazoa
12.
Evolution
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Evolution is change in the heritable characteristics of biological populations over successive generations. Evolutionary processes give rise to biodiversity at every level of organisation, including the levels of species, individual organisms. In July 2016, scientists reported identifying a set of 355 genes from the LUCA of all living on Earth. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, existing patterns of biodiversity have been shaped both by speciation and by extinction. More than 99 percent of all species that lived on Earth are estimated to be extinct. Estimates of Earths current species range from 10 to 14 million, more recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. In the mid-19th century, Charles Darwin formulated the theory of evolution by natural selection. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are fitted for the functional roles they perform. The processes by which the changes occur, from one generation to another, are called evolutionary processes or mechanisms, the four most widely recognized evolutionary processes are natural selection, genetic drift, mutation and gene migration. Natural selection and genetic drift sort variation, mutation and gene migration create variation, consequences of selection can include meiotic drive, nonrandom mating and genetic hitchhiking. In the early 20th century the modern evolutionary synthesis integrated classical genetics with Darwins theory of evolution by natural selection through the discipline of population genetics, the importance of natural selection as a cause of evolution was accepted into other branches of biology. Moreover, previously held notions about evolution, such as orthogenesis, evolutionism, evolutionary computation, a sub-field of artificial intelligence, involves the application of Darwinian principles to problems in computer science. The proposal that one type of organism could descend from another type goes back to some of the first pre-Socratic Greek philosophers, such as Anaximander, such proposals survived into Roman times. The poet and philosopher Lucretius followed Empedocles in his masterwork De rerum natura, in contrast to these materialistic views, Aristotelianism considered all natural things as actualisations of fixed natural possibilities, known as forms. This was part of a teleological understanding of nature in which all things have an intended role to play in a divine cosmic order. In the 17th century, the new method of modern science rejected the Aristotelian approach, however, this new approach was slow to take root in the biological sciences, the last bastion of the concept of fixed natural types. The biological classification introduced by Carl Linnaeus in 1735 explicitly recognized the nature of species relationships. Other naturalists of this time speculated on the change of species over time according to natural laws
13.
Nervous tissue
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Nervous tissue is responsible for sending signals to the brain about suicidal thoughts. Nervous tissue is made up of different types of cells, all of which have an axon. Bundles of axons make up the nerves, functions of the nervous system are sensory input, integration, control of muscles and glands, homeostasis, and mental activity. Nervous tissue is composed of neurons, also called nerve cells, typically, nervous tissue is categorized into four types of tissue. In the central system, the tissue types found are grey matter. In the peripheral nervous system, the types are nerves. The tissue is categorized by its neuronal and neuroglial components, neurons are cells with specialized features that allow them to receive and facilitate nerve impulses, or action potentials, across their membrane to the next neuron. They possess a cell body, with cell projections called dendrites. Dendrites are thin, branching projections that receive electrochemical signaling to create a change in voltage in the cell, axons are long projections that carry the action potential away from the cell body toward the next neuron. The bulb-like end of the axon, called the terminal, is separated from the dendrite of the following neuron by a small gap called a synaptic cleft. When the action potential travels to the terminal, neurotransmitters are released across the synapse and bind to the post-synaptic receptors. Neurons are classified both functionally and structurally and they are the major neuron type in the CNS and include interneurons and motor neurons. These are found in the layer of the cerebellum. Neuroglia encompasses the non-neural cells in tissue that provide various crucial supportive functions for neurons. They are smaller than neurons, and vary in structure according to their function, neuroglial cells are classified as follows, Microglial cells, Microglia are macrophage cells that make up the primary immune system for the CNS. They are the smallest neuroglial cell, astrocytes, Star-shaped macroglial cells with many processes found in the CNS. They are the most abundant cell type in the brain, and are intrinsic to a healthy CNS, oligodendrocytes, CNS cells with very few processes. They form myelin sheaths on the axons of a neuron, which are lipid-based insulation that increases the speed at which the action potential, can travel down the axon
14.
Anatomical terms of location
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Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. All vertebrates have the basic body plan – they are strictly bilaterally symmetrical in early embryonic stages. That is, they have left and right halves if divided down the centre. For these reasons, the directional terms can be considered to be those used in vertebrates. By extension, the terms are used for many other organisms as well. While these terms are standardized within specific fields of biology, there are unavoidable, sometimes dramatic, for example, differences in terminology remain a problem that, to some extent, still separates the terminology of human anatomy from that used in the study of various other zoological categories. The vertebrates and Craniata share a heritage and common structure. To avoid ambiguities this terminology is based on the anatomy of each animal in a standard way, for humans, one type of vertebrate, anatomical terms may differ from other forms of vertebrates. Thus what is on top of a human is the head, whereas the top of a dog may be its back, for example, many species are not even bilaterally symmetrical. In these species, terminology depends on their type of symmetry, all descriptions are with respect to the organism in its standard anatomical position, even when the organism in question has appendages in another position. This helps avoid confusion in terminology when referring to the organism in different postures. In humans, this refers to the body in a position with arms at the side. While the universal vertebrate terminology used in medicine would work in human medicine. Many anatomical terms can be combined, either to indicate a position in two axes simultaneously or to indicate the direction of a movement relative to the body, for example, anterolateral indicates a position that is both anterior and lateral to the body axis. There is no limit to the contexts in which terms may be modified to qualify each other in such combinations. Generally the modifier term is truncated and an o or an i is added in prefixing it to the qualified term, where desirable three or more terms may be agglutinated or concatenated, as in anteriodorsolateral. Such terms sometimes used to be hyphenated, but the tendency is to omit the hyphen. There is however little basis for any rule to interfere with choice of convenience in such usage
15.
Human head
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In human anatomy, the head is the upper portion of the human body. It supports the face and is maintained by the skull, which encloses the brain. The human head consists of an outer portion surrounding the bony skull. The head rests on the neck, and is provided bony support for movement by the seven cervical vertebrae, the face is the anterior part of the head, containing the sensory organs the eyes, nose and mouth. The cheeks, on side of the mouth, provide a fleshy border to the oral cavity. To either side of the sit the ears. The twelve pairs of cranial nerves provide the majority of control to the head. The sensation to the face is provided by the branches of the trigeminal nerve, the sensation to other portions of the head is provided by the cervical nerves. The head receives blood supply through the internal and external carotid arteries and these supply the area outside of the skull and inside of the skull. The area inside the skull also receives blood supply from the vertebral arteries, the head contains sensory organs, two eyes, two ears, a nose and inside the mouth a tongue. The human head typically weighs between 5 and 11 pounds, human faces are easily differentiable to us due to our brains predispositions toward discriminating human facial forms. When observing a relatively unfamiliar species, all faces seem nearly identical, ancient Greeks had a method for evaluating sexual attractiveness based on the Golden Ratio, part of which included measurements of the head. In many cultures, covering the head is seen as a sign of respect, often, some or all of the head must be covered and veiled when entering holy places, or places of prayer. For many centuries, women in Europe, the Middle East and this trend has changed drastically in Europe in the 20th century, although is still observed in other parts of the world. People may cover the head for other reasons, a hat is a piece of clothing covering just the top of the head. This may be part of a uniform, such as a uniform, a protective device such as a hard hat. Different headpieces can also signify status, origin, religious/spiritual beliefs, social grouping, team affiliation, occupation, while numerous charts detailing head sizes in infants and children exist, most do not measure average head circumference past the age of 21. Reference charts for adult head circumference also generally feature homogeneous samples, one study in the United States estimated the average human head circumference to be 55 centimetres in females and 57 centimetres in males
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Head and neck anatomy
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This article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat. The head is positioned upon the portion of the vertebral column. The skeletal section of the head and neck forms the superior segment of the skeleton and comprises skull, hyoid bone, auditory ossicles. The skull can be subdivided into, cranium, and facial bones. As the fetus develops, the facial bones usually form into pairs, as the cranium fuses, sutures are formed that resemble stitching between bone plates. In a newborn, the junction of the bones with the frontal and occipital bones, form the anterior and posterior fontanelle. The separation of the bone plates at time of birth facilitate passage of the head of the fetus through the mothers birth canal. The parietal bones, and occipital bone can overlap each other in the birth canal, the occipital bone articulates with the atlas near the foramen magnum. The atlas articulates with the occipital condyle superiorly and the axis inferiorly, the spinal cord passes through the foramen magnum providing continuity for the central nervous system. Articulation of the neck includes, flexion, extension, and rotation, blood circulates from the upper systemic loop originating at the aortic arch, and includes, the brachiocephalic artery, left common carotid artery and left subclavian artery. The head and neck are emptied of blood by the subclavian vein, the brachiocephalic artery or trunk is the first and largest artery that branches to form the right common carotid artery and the right subclavian artery. This artery provides blood to the upper chest, right arm, neck. The right and left vertebral artery feed into the artery and upward to the Posterior cerebral artery. The posterior cerebral artery and the posterior communicating artery are within the circle of Willis, the left common carotid artery divides to form the, internal carotid artery and an external carotid artery. The ECA supplies the neck and face, the left subclavian artery and the right subclavian artery, one on each side of the body form the internal thoracic artery, the vertebral artery, the thyrocervical trunk, and the costocervical trunk. The subclavian becomes the axiliary artery at the border of the first rib. The left subclavian artery also provides blood to the upper chest. The Blood–brain barrier is semi-permeable membrane that controls the capillary potential of the circulatory system
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Skull
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The skull is a bony structure that forms the head of the skeleton in most vertebrates. It supports the structures of the face and provides a cavity for the brain. The skull is composed of two parts, the cranium and the mandible, in the human these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone. The skull forms the anterior most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, in the human these sensory structures are part of the facial skeleton. In some animals such as horned ungulates, the skull also has a function by providing the mount for the horns. The English word skull is probably derived from Old Norse skulle, while the Latin word cranium comes from the Greek root κρανίον, the skull is made up of a number of fused flat bones, and contains many foramina and processes, and several cavities or sinuses. For details and the constituent bones, see neurocranium and viscerocranium, the human skull is the bony structure that forms the head in the human skeleton. It supports the structures of the face and forms a cavity for the brain, like the skulls of other vertebrates, it protects the brain from injury. The skull consists of two parts, of different embryological origin—the neurocranium and the facial skeleton, the neurocranium forms the protective cranial cavity that surrounds and houses the brain and brainstem. The facial skeleton is formed by the supporting the face. Except for the mandible, all of the bones of the skull are joined together by sutures—synarthrodial joints formed by bony ossification, sometimes there can be extra bone pieces within the suture known as wormian bones or sutural bones. The human skull is considered to consist of twenty-two bones—eight cranial bones. In the neurocranium these are the bone, two temporal bones, two parietal bones, the sphenoid, ethmoid and frontal bones. The bones of the skeleton are the vomer, two nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, two zygomatic bones, and two lacrimal bones. Some of these bones—the occipital, parietal, frontal, in the neurocranium, and the nasal, lacrimal, the skull also contains sinus cavities and numerous foramina. The sinuses are lined with respiratory epithelium and their known functions are the lessening of the weight of the skull, the aiding of resonance to the voice and the warming and moistening of the air drawn through the nasal cavity. The foramina are openings in the skull, the largest of these is the foramen magnum that allows the passage of the spinal cord as well as nerves and blood vessels. The many processes of the include the mastoid process and the zygomatic process
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Mandible
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The mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the face. It forms the lower jaw and holds the teeth in place. The mandible sits beneath the maxilla, the bone is formed from a fusion of left and right processes, and the point where these sides join, the mandibular symphysis, is still visible as a faint ridge in the midline. Like other symphyses in the body, this is a midline articulation where the bones are joined by fibrocartilage, the body of the mandible is curved somewhat like a horseshoe and has two surfaces and two borders. From the outside, the mandible is marked in the midline by a faint ridge and this ridge divides below and encloses a triangular eminence, the mental protuberance, the base of which is depressed in the center but raised on either side to form the mental tubercle. On either side of the symphysis, just below the teeth, is a depression, the incisive fossa, which gives origin to the mentalis. Below the second premolar tooth, on side, midway between the upper and lower borders of the body, is the mental foramen, for the passage of the mental vessels. From the inside, the mandible appears concave, near the lower part of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the genioglossus. Immediately below these is a pair of spines, or more frequently a median ridge or impression. In some cases the mental spines are fused to form a single eminence, in others they are absent, above the mental spines a median foramen and furrow are sometimes seen, they mark the line of union of the halves of the bone. Below the mental spines, on side of the middle line, is an oval depression for the attachment of the anterior belly of the digastric. Above the anterior part of line is a smooth triangular area against which the sublingual gland rests, and below the hinder part. To the outer lip of the border, on either side. The ramus of the mandible has four sides, two surfaces, four borders, and two processes. On the outside, the ramus is flat and marked by oblique ridges at its lower part, on the inside, the mandible presents about its center the oblique mandibular foramen, for the entrance of the inferior alveolar vessels and nerve. Behind this groove is a surface, for the insertion of the internal pterygoid muscle. The mandibular canal runs obliquely downward and forward in the ramus, and then horizontally forward in the body, on arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor teeth. In the posterior two-thirds of the bone the canal is situated nearer the surface of the mandible
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Cranial cavity
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The cranial cavity, or intracranial space, is the space formed inside the skull. It is part of the body cavity. The brain occupies the cranial cavity, which is lined by the meninges, eight fused cranial bones together form the cranial cavity, the frontal, occipital, sphenoid and ethmoid bones, and two each of the parietal and temporal bones. The capacity of an adult human cranial cavity is 1, 200-1,700 cm3, neurocranium Intracranial pressure Anatomy of cranial cavity
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Facial skeleton
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The facial skeleton, viscerocranium, or splanchnocranium consists of a part of the skull that is derived from the pharyngeal arches. The facial bones are the bones of the anterior and lower skull, the rest of the skull is the neurocranium. The ethmoid bone and also the sphenoid bone are sometimes included, some sources describe the maxillas left and right parts as two bones. Likewise, the bone is also sometimes described as two bones. Textbooks differ as to what bones to include in the facial skeleton, some textbooks make a strict distinction between bones of the neurocranium and viscerocranium, based on the embryological origins of the bones. Other textbooks tend to all the bones that can be seen in a frontal aspect of the human skull. The viscerocranium is derived from the neural crest cells or from the sclerotome, as with the neurocranium, in Chondricthyes and other cartilaginous vertebrates, they are not replaced via endochondral ossification. In tetrapods, such as amphibians and reptiles, the connecting to the tympanum is derived from the splanchnocranium. In mammals, the splanchnocranium derives the bones of the ear, the malleus. Variation in craniofacial form between humans is due to differing patterns of biological inheritance. Cross-analysis of osteological variables and genome-wide SNPs has identified specific genes, of these genes, DCHS2, RUNX2, GLI3, PAX1 and PAX3 were found to determine nasal morphology, whereas EDAR impacts chin protrusion. Face ent/9 at eMedicine - Facial Bone Anatomy
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Jaw
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The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. In arthropods, the jaws are chitinous and oppose laterally, and these jaws are often composed of numerous mouthparts. Their function is fundamentally for food acquisition, conveyance to the mouth, many mouthparts and associate structures are modified legs. In most vertebrates, the jaws are bony or cartilaginous and oppose vertically, comprising an upper jaw, the vertebrate jaw is derived from the most anterior two pharyngeal arches supporting the gills, and usually bears numerous teeth. The vertebrate jaw probably originally evolved in the Silurian period and appeared in the Placoderm fish which further diversified in the Devonian, the two most anterior pharyngeal arches are thought to have become the jaw itself and the hyoid arch, respectively. The hyoid system suspends the jaw from the braincase of the skull and it is thought that the original selective advantage offered by the jaw was not related to feeding, but to increased respiration efficiency. The jaws were used in the pump that pumps water across the gills of fish or air into the lungs in the case of amphibians. Over evolutionary time the familiar use of jaws, in feeding, was selected for. Many teleost fish have substantially modified jaws for feeding and jaw protrusion. The jaw in tetrapods is substantially simplified compared to fish, most of the upper jaw bones have been fused to the braincase, while the lower jaw bones have been fused together into a unit called the mandible. The jaw articulates via a joint between the quadrate and articular. The jaws of tetrapods exhibit varying degrees of mobility between jaw bones, some species have jaw bones completely fused, while others may have joints allowing for mobility of the dentary, quadrate, or maxilla. The snake skull shows the greatest degree of cranial kinesis, which allows the snake to swallow large prey items. In the evolution of the jaw, two of the bones of the jaw structure were reduced in size and incorporated into the ear. As a result, mammals show little or no cranial kinesis, temporomandibular joint dysfunction is a common disorder of these joints, characterized by pain, clicking and limitation of mandibular movement. Sea urchins possess unique jaws which display five-part symmetry, termed the Aristotles lantern, each unit of the jaw holds a single, perpetually growing tooth composed of crystalline calcium carbonate. Gnathostomata – jawed vertebrates Muscles of mastication Otofacial syndrome Predentary Premaxilla Prognathism Rostral bone Tooth Jaw at the US National Library of Medicine Medical Subject Headings
22.
Cheekbone
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In the human skull, the zygomatic bone is a paired bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. It is situated at the upper and lateral part of the face and forms the prominence of the cheek, part of the wall and floor of the orbit. It presents a malar and a surface, four processes, the frontosphenoidal, orbital, maxillary, and temporal. Near the center of surface is the zygomaticotemporal foramen for the transmission of the zygomaticotemporal nerve. The orbital surface forms the part and some of the inferior part of the bony orbit. The zygomatic nerve passes through the foramen on this surface. The lateral palpebral ligament attaches to a small protuberance called the orbital tubercle, each zygomatic bone is diamond-shaped and composed of three processes with similarly named associated bony articulations, frontal, temporal, and maxillary. Each process of the bone forms important structures of the skull. The orbital surface of the process of the zygomatic bone forms a part of the infraorbital rim. The antero-superior or orbital border is smooth, concave, and forms a part of the circumference of the orbit. The postero-inferior or zygomatic border affords attachment by its edge to the Masseter. The zygomatic articulates with four bones, the frontal, sphenoid, temporal, mall describes it as being ossified from one center which appears just beneath and to the lateral side of the orbit. After birth, the bone is sometimes divided by a suture into an upper larger. In some quadrumana the zygomatic bone consisted of two parts, an orbital and a malar, high cheekbones are pronounced zygomatic arches, causing the upper part of the cheeks to jut out and form a line cut into the sides of the face. High cheekbones, forming a face shape, are very common in fashion models and are considered a beauty trait in both males and females. The term zygomatic derives from the Greek Ζυγόμα zygoma meaning yoke, the zygomatic bone is occasionally referred to as the zygoma, but this term may also refer to the zygomatic arch. The zygomatic is homologous to the bone of other tetrapods. In non-mammalian vertebrates, the bone is referred to as the jugal bone
23.
John Searle
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John Rogers Searle is an American philosopher and currently the Slusser Professor Emeritus of Philosophy at the University of California, Berkeley. Widely noted for his contributions to the philosophy of language, philosophy of mind and social philosophy and he received the Jean Nicod Prize in 2000, the National Humanities Medal in 2004, and the Mind & Brain Prize in 2006. Among his notable concepts is the Chinese room argument against strong artificial intelligence, Searles father, G. W. Searle, an electrical engineer, was employed by AT&T Corporation, while his mother, Hester Beck Searle, was a physician. A. His first two faculty jobs were in Oxford as Research Lecturer and Lecturer and Tutor at Christ Church and he has five honorary doctorate degrees from four different countries and is an honorary visiting professor at Tsing Hua University and East China Normal University. While an undergraduate at the University of Wisconsin, Searle was the secretary of Students against Joseph McCarthy, McCarthy was then the junior senator from Wisconsin. In 1959, Searle began to teach at Berkeley and was the first tenured professor to join the 1964–5 Free Speech Movement, in The Campus War, A Sympathetic Look at the University in Agony, Searle investigates the causes behind the campus protests of the era. In it he declares that, I have been attacked by both the House Un-American Activities Committee and, stylistically, the attacks are interestingly similar. Both rely heavily on insinuation and innuendo, and both display a hatred – one might almost say terror – of close analysis and dissection of argument and he asserts that My wife was threatened that I would be assassinated or violently attacked. In the late 1980s, Searle, along with other landlords, the rental board refused to consider Searles petition and Searle filed suit, charging a violation of due process. The court described the debate as a morass of political invective, ad hominem attack and he called for the realization that the US is in a more-or-less permanent state of war with these forces. Moreover, a course of action would be to deny terrorists the use of foreign territory from which to stage their attacks. Finally, he alluded to the nature of the conflict. In March 2017, Searle was the subject of sexual assault allegations, Berkeleys alleged protection of Searle was seen in some quarters as a recurrence of earlier problems in dealing with similar accusations against other staff. The suit, filed in a California court on March 21,2017 and it was reported that n early March, Searle’s students learned he would no longer be teaching his undergraduate Philosophy of Mind course. Beyond citing personal reasons, university officials provided no explanation for Searle’s departure, Searles early work, which did a great deal to establish his reputation, was on speech acts. He attempted to synthesize ideas from many colleagues – including J. L. Austin, Ludwig Wittgenstein, midgley – with his own thesis that such acts are constituted by the rules of language. He also drew on the work of H. Paul Grice, Hare and Stenius, strawson, John Rawls and William P. In his 1969 book Speech Acts, Searle sets out to all these elements to give his account of illocutionary acts
24.
Brain
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The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head, usually close to the organs for senses such as vision. The brain is the most complex organ in a vertebrates body, in a human, the cerebral cortex contains approximately 15–33 billion neurons, each connected by synapses to several thousand other neurons. Physiologically, the function of the brain is to exert centralized control over the other organs of the body, the brain acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows rapid and coordinated responses to changes in the environment, the operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be solved. This article compares the properties of brains across the range of animal species. It deals with the human brain insofar as it shares the properties of other brains, the ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because more can be said about them in a human context. The most important is brain disease and the effects of brain damage, the shape and size of the brain varies greatly between species, and identifying common features is often difficult. Nevertheless, there are a number of principles of architecture that apply across a wide range of species. Some aspects of structure are common to almost the entire range of animal species, others distinguish advanced brains from more primitive ones. The simplest way to gain information about brain anatomy is by visual inspection, Brain tissue in its natural state is too soft to work with, but it can be hardened by immersion in alcohol or other fixatives, and then sliced apart for examination of the interior. Visually, the interior of the consists of areas of so-called grey matter, with a dark color, separated by areas of white matter. Further information can be gained by staining slices of tissue with a variety of chemicals that bring out areas where specific types of molecules are present in high concentrations. It is also possible to examine the microstructure of brain tissue using a microscope, the brains of all species are composed primarily of two broad classes of cells, neurons and glial cells. Glial cells come in types, and perform a number of critical functions, including structural support, metabolic support, insulation. Neurons, however, are considered the most important cells in the brain. The property that makes neurons unique is their ability to send signals to target cells over long distances
25.
Sagittal plane
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A sagittal plane is an anatomical plane which divides the body into right and left parts. The plane may be in the centre of the body and split it into two halves or away from the midline and split it into unequal parts, most elements of Irish dancing occur in the sagittal plane. Examples include, The terms median plane or mid-sagittal plane are sometimes used to describe the sagittal plane running through the midline and this plane cuts the body into halves, passing through midline structures such as the navel and spine. It is one of the planes which, combined with the Umbilical plane, the term parasagittal is used to describe any plane parallel to the sagittal plane. In practice, such a section is referred to simply as a sagittal view because viewing is achieved along the sagittal axis. Owing to the nature of its definition, only one true sagittal plane exists. Be aware that the term sagittal view may be applied to any parasagittal section as well as the sagittal plane, specific named parasagittal planes include, The midclavicular line crosses through the clavicle. Other sagittal lines/planes include the lateral sternal and parasternal, the term sagittal is derived from the Latin word sagitta, meaning arrow. An image of an arrow piercing a body and passing from front to back on a trajectory would be one way to demonstrate the derivation of the term. Another explanation would be the notching of the sagittal suture posteriorly by the lambdoidal suture —similar to feathers on an arrow, extension and flexion are the movements of limbs within the sagittal plane. Abduction and adduction are terms for movements of limbs within the coronal plane, anatomical terms of location Coronal plane Transverse plane
26.
Thomas Bartholin
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Thomas Bartholin was a Danish physician, mathematician, and theologian. He is best known for his work in the discovery of the system in humans and for his advancements of the theory of refrigeration anesthesia. Thomas Bartholin came from a family that has become famous for its pioneering scientists, Thomas Bartholins son Thomas Bartholin the Younger became a professor of history at the University of Copenhagen and was later appointed royal antiquarian and secretary to the Royal Archives. Thomas Bartholin was the second of the six sons of Caspar Bartholin the Elder, Bartholin the Elder published the first collected anatomical work in 1611. Bartholin visited the Italian botanist Pietro Castelli at Messina in 1644, in 1663 Bartholin bought Hagestedgaard, which burned down in 1670 including his library, with the loss of many manuscripts. King Christian V of Denmark appointed Bartholin as his physician with a substantial salary, in 1680 Bartholins health failed, the farm was sold, and he moved back to Copenhagen, where he died. He was buried in Vor Frue Kirke, the Bartholinsgade, a street in Copenhagen, is named for the family. One of the buildings of the University of Aarhus is named after him, in December 1652, Bartholin published the first full description of the human lymphatic system. As a result, a priority dispute ensued. Niels Stensen or Steno became his most famous pupil, according to Bartholin, Severino was the first to present the use of freezing mixtures of snow and ice, and Thomas Bartholin initially learnt about the technique from him during a visit to Naples. Bartholin–Patau syndrome, first described by Thomas Bartholin, is a syndrome of multiple abnormalities produced by trisomy 13. Centuria I et II at Google Books, Amsterdam,1654, centuria III et IV at Google Books. Centuria V et VI at Google Books, Copenhagen, P. Haubold,1661, De lacteis thoracicis in homine brutisque nuperrime observatis historia anatomica at Google Books, Copenhagen, M. Martzan,1652. Vasa lymphatica nuper Hafniae in animalibus inventa et hepatis exsequiae, vasa lymphatica in homine nuper inventa. De nivis usu medico observationes variae, accessit D. Erasmi Bartholini de figura nivis dissertatio. With a book by Rasmus Bartholin, Copenhagen, Typis Matthiase Godichii, sumptibus Petri Haubold,1661. Orationes et dissertationes omnino varii argumenti, De cruce Christi hypomnemata IV, Typis Andreae ab Hoogenhuysen, Vesaliae,1673. View digitized titles by Thomas Bartholin in Botanicus. org Thomas Bartholin in Whonamedit. com Bartholins De luce animalium – digital facsimile at the Linda Hall Library
27.
Cephalon (arthropod head)
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The cephalon is the head section of an arthropod. It is a tagma, i. e. a specialized grouping of arthropod segments, the word cephalon derives from the Greek κεφαλή, meaning head. In insects, head is a preferred term, in chelicerates and crustaceans, the cephalothorax is derived from the fusion of the cephalon and the thorax, and is usually covered by a single unsegmented carapace. In the Late Precambrian or Lower Cambrian Proarticulata species Praecambridium sigillum, that resembles a trilobite. The head of the Thylacocephala is also referred to as a cephalon, the cephalon of trilobites is highly variable with a lot of morphological complexity. The glabella, the expression of the lobe in the cephalon. A toothless mouth and stomach sat upon the hypostome with the mouth facing backwards at the edge of the hypostome. Many variations in shape and placement of the hypostome have been described, the size of the glabella and the lateral fringe of the cephalon, together with hypostome variation, have been linked to different lifestyles, diets and specific ecological niches. The lateral fringe of the cephalon is greatly exaggerated in the Harpetida, highly complex compound eyes are another obvious feature of the cephalon. When trilobites moulted, the librigenae separated along the suture to assist moulting, leaving the cranidium exposed. Trilobite facial sutures can be divided into three main types according to where the sutures end relative to the genal angle. Early Cambrian trilobites belonging to the suborder Olenellina lacked facial sutures, other later trilobites also lost facial sutures secondarily. Carapace Facial suture Pygidium Tagma Thorax
28.
Arthropod
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An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages. Arthropods form the phylum Arthropoda, which includes the insects, arachnids, myriapods, arthropods are characterized by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages, the rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Their versatility has enabled them to become the most species-rich members of all guilds in most environments. They have over a million described species, making up more than 80% of all described living species, some of which. Arthropods range in size from the microscopic crustacean Stygotantulus up to the Japanese spider crab, arthropods primary internal cavity is a hemocoel, which accommodates their internal organs, and through which their haemolymph – analogue of blood – circulates, they have open circulatory systems. Like their exteriors, the organs of arthropods are generally built of repeated segments. Their nervous system is ladder-like, with paired ventral nerve cords running through all segments and their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong, arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many setae that project through their cuticles. Aquatic species use internal or external fertilization. Almost all arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother, arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form. The level of care for hatchlings varies from nonexistent to the prolonged care provided by scorpions. The evolutionary ancestry of arthropods dates back to the Cambrian period, the group is generally regarded as monophyletic, and many analyses support the placement of arthropods with cycloneuralians in a superphylum Ecdysozoa. Overall however, the relationships of Metazoa are not yet well resolved. Likewise, the relationships between various groups are still actively debated. Arthropods contribute to the food supply both directly as food, and more importantly indirectly as pollinators of crops. Some species are known to spread disease to humans, livestock. The word arthropod comes from the Greek ἄρθρον árthron, joint, and πούς pous, i. e. foot or leg, arthropods are invertebrates with segmented bodies and jointed limbs
29.
Trilobite
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Trilobites are a fossil group of extinct marine arachnomorph arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods, Trilobites finally disappeared in the mass extinction at the end of the Permian about 250 million years ago. The trilobites were among the most successful of all early animals, by the time trilobites first appeared in the fossil record, they were already highly diversified and geographically dispersed. Because trilobites had wide diversity and an easily fossilized exoskeleton, a fossil record was left behind. The study of fossils has facilitated important contributions to biostratigraphy, paleontology, evolutionary biology. Trilobites are often placed within the arthropod subphylum Schizoramia within the superclass Arachnomorpha, Trilobites had many lifestyles, some moved over the sea bed as predators, scavengers, or filter feeders, and some swam, feeding on plankton. Most lifestyles expected of modern marine arthropods are seen in trilobites, some trilobites are even thought to have evolved a symbiotic relationship with sulfur-eating bacteria from which they derived food. The earliest trilobites known from the record are redlichiids and ptychopariid bigotinids dated to some 540 to 520 million years ago. Contenders for the earliest trilobites include Profallotaspis jakutensis, Fritzaspis spp, all trilobites are thought to have originated in present-day Siberia, with subsequent distribution and radiation from this location. All Olenellina lack facial sutures, and this is thought to represent the original state, other groups show secondary lost facial sutures, such as all Agnostina and some Phacopina. Earlier trilobites may be found and could shed light on the origin of trilobites. Three specimens of a trilobite from Morocco, Megistaspis hammondi, dated 478 million years old contain fossilized soft parts. Early trilobites show all the features of the group as a whole. Morphological similarities between early trilobites and other Cambrian arthropods make analysis of ancestral relationships difficult, however, that trilobites share a common ancestor with other arthropods before the Ediacaran-Cambrian boundary is still reasonable to assume. Changes also included narrowing of the thorax and increasing or decreasing numbers of thoracic segments, specific changes to the cephalon are also noted, variable glabella size and shape, position of eyes and facial sutures, and hypostome specialization. Several morphologies appeared independently within different major taxa, effacement, the loss of surface detail in the cephalon, pygidium, or the thoracic furrows, is also a common evolutionary trend. Notable examples of this were the orders Agnostida and Asaphida, effacement is believed to be an indication of either a burrowing lifestyle or a pelagic one. Effacement poses a problem for taxonomists since the loss of details can make the determination of phylogenetic relationships difficult, tectonic breakup of Pannotia then allowed for the diversification and radiation expressed later in the Cambrian as the distinctive olenellid province and the separate redlichid province
30.
Nomada
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With over 850 species, the genus Nomada is one of the largest genera in the family Apidae, and the largest genus of cleptoparasitic cuckoo bees. They occur worldwide, and use different types of bees as hosts. As parasites, they lack a pollen-carrying scopa, and are often extraordinarily wasp-like in appearance, with red, black, and yellow colors prevailing, see List of Nomada species for a complete list. C. D. Michener The Bees of the World, Johns Hopkins University Press
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Bee
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Bees are flying insects closely related to wasps and ants, known for their role in pollination and, in the case of the best-known bee species, the European honey bee, for producing honey and beeswax. Bees are a lineage within the superfamily Apoidea, presently considered as a clade Anthophila. There are nearly 20,000 known species of bees in seven to nine recognized families, though many are undescribed and they are found on every continent except Antarctica, in every habitat on the planet that contains insect-pollinated flowering plants. Some species including honey bees, bumblebees, and stingless bees live socially in colonies, Bees are adapted for feeding on nectar and pollen, the former primarily as an energy source and the latter primarily for protein and other nutrients. Most pollen is used as food for larvae, Bee pollination is important both ecologically and commercially, the decline in wild bees has increased the value of pollination by commercially managed hives of honey bees. The most common bees in the Northern Hemisphere are the Halictidae, or sweat bees, vertebrate predators of bees include birds such as bee-eaters, insect predators include beewolves and dragonflies. Human beekeeping or apiculture has been practised for millennia, since at least the times of Ancient Egypt, apart from honey and pollination, honey bees produce beeswax, royal jelly and propolis. Bees have appeared in mythology and folklore, again since ancient times, and they feature in works of literature as varied as Virgils Georgics, Beatrix Potters The Tale of Mrs Tittlemouse, yeatss poem The Lake Isle of Innisfree. Bee larvae are included in the Javanese dish botok tawon, where they are steamed with shredded coconut. The ancestors of bees were wasps in the family Crabronidae, which were predators of other insects. The switch from insect prey to pollen may have resulted from the consumption of insects which were flower visitors and were partially covered with pollen when they were fed to the wasp larvae. This same evolutionary scenario may have occurred within the vespoid wasps, until recently, the oldest non-compression bee fossil had been found in New Jersey amber, Cretotrigona prisca of Cretaceous age, a corbiculate bee. A bee fossil from the early Cretaceous, Melittosphex burmensis, is considered an extinct lineage of pollen-collecting Apoidea sister to the modern bees. Derived features of its place it clearly within the bees. By the Eocene there was considerable diversity among eusocial bee lineages. The highly eusocial corbiculate Apidae appeared roughly 87 Mya, and the Allodapini around 53 Mya, the Colletidae appear as fossils only from the late Oligocene to early Miocene. The Melittidae are known from Palaeomacropis eocenicus in the Early Eocene, the Megachilidae are known from trace fossils from the Middle Eocene. The Andrenidae are known from the Eocene-Oligocene boundary, around 34 Mya, the Halictidae first appear in the Early Eocene with species found in amber
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Antenna (biology)
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Antennae, sometimes referred to as feelers, are paired appendages used for sensing in arthropods. Antennae are connected to the first one or two segments of the arthropod head and they vary widely in form, but are always made of one or more jointed segments. While they are sensory organs, the exact nature of what they sense. Functions may variously include sensing touch, air motion, heat, vibration, antennae are sometimes modified for other purposes, such as mating, brooding, swimming, and even anchoring the arthropod to a substrate. Larval arthropods have antennae that differ from those of the adult, many crustaceans, for example, have free-swimming larval forms that use their antennae for swimming. Except the chelicerates and proturans, which have none, all non-crustacean arthropods have a pair of antennae. Crustaceans bear two pairs of antennae, the pair attached to the first segment of the head are called primary antennae or antennules. This pair is generally uniramous, but is biramous in crabs and lobsters, the pair attached to the second segment are called secondary antennae or simply antennae. The second antennae are biramous, but many species later evolved uniramous pairs. The second antennae may be reduced, apparently absent, or modified to such an extent that they no longer resemble antennae. The subdivisions of crustacean antennae have many names, including flagellomeres, annuli, articles, the terminal ends of crustacean antennae have two major categorizations, segmented and flagellate. An antenna is considered segmented if each of the annuli is separate from those around it and has individual muscle attachments. Flagellate antennae, on the hand, have muscle attachments only around the base. There are several notable uses of antennae in crustaceans. Many crustaceans have a larval stage called a nauplius, which is characterized by its use of antennae for swimming. Barnacles, a highly modified crustacean, use their antennae to attach to rocks, insects evolved from prehistoric crustaceans, and they have secondary antennae like crustaceans, but not primary antennae. Antennae are the primary olfactory sensors of insects and are accordingly well-equipped with a variety of sensilla. Paired, mobile, and segmented, they are located between the eyes on the forehead, embryologically, they represent the appendages of the second head segment
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Simple eye in invertebrates
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A simple eye refers to a type of eye form or optical arrangement that contains a single lens. A simple eye is so called in distinction from a compound eye. The eyes of humans and large animals, and camera lenses are classed as simple because in both cases a single lens collects and focuses light onto the retina or film. Many insects have compound eyes consisting of multiple lenses, each focusing light onto a number of retinula cells. The structure of an eye is determined by the environment in which it lives. Arthropods differ widely in the habitats in which live, as well as their visual requirements for finding food or conspecifics. Consequently, a variety of eye designs are found in arthropods. Some jellyfish, sea stars, and flatworms bear the simplest eyes, pigment spot ocelli, which have pigment distributed randomly, the apparent eye color in these animals is therefore red or black. However, other cnidaria have more complex eyes, including those of Cubomedusae which have distinct retina, lens, many snails and slugs also have ocelli, either at the tips or at the bases of the tentacles. However, some gastropods, such as the Strombidae, have much more sophisticated eyes. Giant clams have ocelli that allow light to penetrate their mantles, spiders do not have compound eyes, but instead have several pairs of simple eyes with each pair adapted for a specific task or tasks. The principal and secondary eyes in spiders are arranged in four or more pairs, only the principal eyes have moveable retinas. The secondary eyes have a reflector at the back of the eyes, the light-sensitive part of the receptor cells is next to this, so they get direct and reflected light. In hunting or jumping spiders, for example, a forward-facing pair possesses the best resolution to see the prey at a large distance, night-hunting spiders eyes are very sensitive in low light levels with a large aperture, f/0.58. The term ocellus is derived from the Latin oculus, and literally means little eye, two distinct ocellus types exist, dorsal ocelli, found in most insects, and lateral ocelli, which are found in the larvae of some insect orders. They are structurally and functionally very different, simple eyes of other animals, e. g. cnidarians, may also be referred to as ocelli, but again the structure and anatomy of these eyes is quite distinct from those of the dorsal ocelli of insects. Dorsal ocelli are light-sensitive organs found on the surface or frontal surface of the head of many insects, e. g. Hymenoptera, Diptera, Odonata. The ocelli coexist with the eyes, thus most insects possess two anatomically separate and functionally different visual pathways
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Labrum (arthropod mouthpart)
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The labrum is a flap-like structure that lies immediately in front of the mouth in almost all extant Euarthropoda. The most conspicuous exceptions are the Pycnogonida, which probably are chelicerate-relatives, in entomology, the labrum amounts to the upper lip of an insect mouth, the corresponding lower lip being the labium. The evolutionary origin, embryogenesis and morphological development of the labrum have proved to be by far the most controversial, the labrum is innervated in crustaceans and insects from the tritocerebrum, i. e. the back of the brain. However, in development its embryonic primordium often appears at the anterior of the head, furthermore, it often appears as a bilobed structure, with a set of muscles, nerves and gene expression in many ways similar to that of an appendage. This evidence has been used to suggest that the labrum is in fact a highly reduced appendage. If the labrum is a then it seems possible that its origin is indicated by its developmentally anterior position. The most obvious choice for this is the segment whose ganglion is the protocerebrum and it has even been suggested that the labrum belongs to an even more obscure segment that lies in front of the ocular one. However, most subsequent work in the first decade of the 21st century has tended to support for the impression that the labrum is indeed appendiculate in origin. Evidence of varied origin and nature, though not qualitatively uniform in all Arthropoda, there do remain difficulties however, the labrum develops in median tissues rather than the lateral sources expected of paired appendages and is part of an anterior nonsegmental tissue. Another line of evidence arose from a study of the external morphology during the embryogenesis of members of the Mecoptera and it too suggests that the labrum derives from paired appendages
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Maxilla (arthropod mouthpart)
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In arthropods, the maxillae are paired structures present on the head as mouthparts in members of the clade Mandibulata, used for tasting and manipulating food. In most cases, two pairs of maxillae are present and in different arthropod groups the two pairs of maxillae have been variously modified, in crustaceans, the first pair are called maxillulae. Modified coxae at the base of the pedipalps in spiders are also called maxillae, the gnathochilarium is richly infused with chemosensory and tactile receptors along its edge. In centipedes, both pairs of maxillae are developed, the first maxillae are situated ventrally to the mandibles and obscure them from view. The second maxillae, which cover the first maxillae, consist of only a telopodite. The telopodite is recognizably leglike in structure and consists of three plus a apical claw. The second maxillae also have a pore, which is the opening of the maxillary gland. In crustaceans, the two pairs of maxillae are called maxillulae and maxillae and they serve to transport food to the mandibles but also frequently help in the filtration process and additionally they may sometimes play a role in cleaning and grooming. These structures show an incredible diversity throughout crustaceans but generally are much flattened. The two pairs are normally positioned very close together and their apical parts generally are in contact with the mandible. The lacinia is often strongly sclerotized and toothed and it functions to cut and manipulate food in the mouth. The galea is a broad, scoop-like, lobe structure, which assists the maxillary palps in sampling items before ingestion. The maxillary palp is serially homologous to the leg while the cardo and stipes are regarded by most to be serially homologous to the first leg segment. It consists of a basal submentum, which connects with the prementum through a narrow sclerite, the labium forms the lower portion of the buccal cavity in insects. The prementum has a pair of labial palps laterally, and two soft lobes called the paraglossae medially. These paraglossae have two small slender lobes called glossae at their base, in many hexapods, the mouthparts have been modified for different functions and the maxillae and labium can change in structure greatly. In bees, the maxillae and labium have been modified and fused to form a nectar-sucking proboscis, in the order Hemiptera, the true bugs, plant hoppers, etc. the mouthparts have been modified to form a beak for piercing. The labium forms a sheath around a set of stylets that consist of a pair of mandibles
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Arthropod mouthparts
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The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired appendages, which in ancestral forms would have appeared more like legs than mouthparts, in general, arthropods have mouthparts for cutting and chewing, piercing and sucking, siphoning, and filtering. This article outlines the elements of four arthropod groups, insects, myriapods, crustaceans. Insects are used as the model, with the mouthparts of the other groups introduced in turn. Insects are not, however, the form of the other arthropods discussed here. Insect mouthparts exhibit a range of forms, the earliest insects had chewing mouthparts. Specialisation includes mouthparts modified for siphoning, piercing, sucking and sponging and these modifications have evolved a number of times. For example, mosquitoes and aphids both pierce and suck, however, female mosquitoes feed on animal blood whereas aphids feed on plant fluids and this section provides an overview of the individual mouthparts of chewing insects. The labrum is a extension of the head, covering the mandibles. Unlike other mouthparts, the labrum is a single, fused plate and it is the upper-most of the mouthparts and located on the midline. It serves to hold food in place during chewing by the mandibles, chewing insects have two mandibles, one on each side of the head. They are typically the largest mouthpart of chewing insects, being used to food items. They open outwards and come together medially, paired maxillae cut food and manipulate it during mastication. Maxillae can have hairs and teeth along their inner margins, at the outer margin, the galea is a cupped or scoop-like structure, which sits over the outer edge of the labium. They also have palps, which are used to sense the characteristics of potential foods, the labium is a single structure, although it is formed from two fused secondary maxillae. It can be described as the floor of the mouth and functioning in close the mouth of the insect, with the maxillae, it assists manipulation of food during mastication. The hypopharynx is a globular structure, arising from the base of the labium. It performs the role of the found in large vertebrates
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Invertebrate
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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 insects, crabs, lobsters and their kin, snails, clams, octopuses and their kin, starfish, sea-urchins and their kin, jellyfish, and worms. The majority of species are invertebrates, one estimate puts the figure at 97%. Many invertebrate taxa have a number and variety of species than the entire subphylum of Vertebrata. Some of the invertebrates, such as the Tunicata and Cephalochordata are more closely related to the vertebrates than to other invertebrates. This makes the term invertebrate paraphyletic and hence almost meaningless for taxonomic purposes, the word invertebrate comes from the form of the Latin word vertebra, which means a joint in general, and sometimes specifically a joint from the spinal column of a vertebrate. In turn the jointed aspect of vertebra derived from the concept of turning, coupled with the prefix in-, meaning not or without. The term invertebrates is not always precise among non-biologists since it does not accurately describe a taxon in the way that Arthropoda. Each of these describes an valid taxon, phylum, subphylum or family. Invertebrata is a term of convenience, not a taxon, it has very little circumscriptional significance except within the Chordata, 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. That would at least circumscribe the Chordata, however, even the notochord would be a less fundamental criterion than aspects of embryological development and symmetry or perhaps bauplan. The following text reflects earlier scientific understanding of the term and of animals which have constituted it. According to this understanding, invertebrates do not possess a skeleton of bone and they include hugely varied body plans. Many have fluid-filled, hydrostatic skeletons, like jellyfish or worms, others have hard exoskeletons, outer shells like those of insects and crustaceans. The most familiar invertebrates include the Protozoa, Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Echinodermata, Mollusca, Arthropoda include insects, crustaceans and arachnids. By far the largest number of described 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, the trait that is common to all invertebrates is the absence of a vertebral column, this creates a distinction between invertebrates and vertebrates
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Chordate
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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
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Tunicate
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A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata, which is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords. The subphylum was at one time called Urochordata, and the term urochordates is still used for these animals. Some tunicates live as solitary individuals, but others replicate by budding and become colonies and they are marine filter feeders with a water-filled, sac-like body structure and two tubular openings, known as siphons, through which they draw in and expel water. During their respiration and feeding, they take in water through the incurrent siphon, various species are commonly known as sea squirts, sea pork, sea livers, or sea tulips. The earliest probable species of tunicate appears in the record in the early Cambrian period. Their name derives from their outer covering or tunic, which is formed from proteins and carbohydrates. In some species, it is thin, translucent, and gelatinous, while in others it is thick, tough, about 2,150 species of tunicate exist in the worlds oceans, living mostly in shallow water. The most numerous group is the ascidians, fewer than 100 species of these are found at greater than 200 m. Some are solitary animals leading a sessile existence attached to the seabed, but others are colonial and a few are pelagic. Some are supported by a stalk, but most are attached directly to a substrate and they are found in a range of solid or translucent colours and may resemble seeds, grapes, peaches, barrels, or bottles. One of the largest is a stalked sea tulip, Pyura pachydermatina, the Tunicata were established by Jean-Baptiste Lamarck in 1816. In 1881, Francis Maitland Balfour introduced a name for the same group, Urochorda. Accordingly, the current trend is to abandon the name Urochorda or Urochordata in favour of the original Tunicata, and it is accepted as valid by the World Register of Marine Species but not by the Integrated Taxonomic Information System. Various common names are used for different species, sea tulips are tunicates with colourful bodies supported on slender stalks. Sea squirts are so named because of their habit of contracting their bodies sharply, sea liver and sea pork get their names from the resemblance of their dead colonies to pieces of meat. Tunicates are more related to craniates, than to lancelets, echinoderms, hemichordates. The clade consisting of tunicates and vertebrates is called Olfactores, although the traditional classification is provisionally accepted, newer evidence suggests the Ascidiacea are an artificial group of paraphyletic status. Undisputed fossils of tunicates are rare, the best known and earliest unequivocally identified species is Shankouclava shankouense from the Lower Cambrian Maotianshan Shale at Shankou village, Anning, near Kunming
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