A flatfish is a member of the order Pleuronectiformes of ray-finned demersal fishes called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through or around the head during development; some species face their left sides upward, some face their right sides upward, others face either side upward. Many important food fish are in this order, including the flounders, turbot and halibut; some flatfish can camouflage themselves on the ocean floor. Over 700 species are in the 11 families; the largest families are Bothidae, Paralichthyidae and Soleidae, with more than 100 species each. Some families are the results of recent splits. For example, the Achiridae were classified as a subfamily of Soleidae in the past, the Samaridae were considered a subfamily of the Pleuronectidae; the families Paralichthodidae and Rhombosoleidae were traditionally treated as subfamilies of Pleuronectidae, but are now recognised as families in their own right.
The taxonomy of some groups is in need of a review, as the last monograph covering the entire order was John Roxborough Norman's Monograph of the Flatfishes published in 1934. New species are described with some regularity and undescribed species remain. Hybrids are well known in flatfishes; the Pleuronectidae, of marine fishes, have the largest number of reported hybrids. Two of the most famous intergeneric hybrids are between the European plaice and European flounder in the Baltic Sea, between the English sole and starry flounder in Puget Sound; the offspring of the latter species pair is popularly known as the hybrid sole and was believed to be a valid species in its own right. Flatfishes are found in oceans worldwide, ranging from the Arctic, through the tropics, to Antarctica. Most species are found in depths between 0 and 500 m, but a few have been recorded from depths in excess of 1,500 m. None have been confirmed from the hadal zones. An observation of a flatfish from the Bathyscaphe Trieste at the bottom of the Mariana Trench at a depth of 11 km has been questioned by fish experts, recent authorities do not recognize it as valid.
Among the deepwater species, Symphurus thermophilus lives in congregating around "ponds" of sulphur at hydrothermal vents on the seafloor. No other flatfish is known from hydrothermal vents. Many species will enter brackish or fresh water, a smaller number of soles and tonguefish are restricted to fresh water; the most obvious characteristic of the flatfish is its asymmetry, with both eyes lying on the same side of the head in the adult fish. In some families, the eyes are on the right side of the body, in others, they are on the left; the primitive spiny turbots include equal numbers of right- and left-sided individuals, are less asymmetrical than the other families. Other distinguishing features of the order are the presence of protrusible eyes, another adaptation to living on the seabed, the extension of the dorsal fin onto the head; the surface of the fish facing away from the sea floor is pigmented serving to camouflage the fish, but sometimes with striking coloured patterns. Some flatfishes are able to change their pigmentation to match the background, in a manner similar to some cephalopods.
The side of the body without the eyes, facing the seabed, is colourless or pale. In general, flatfishes rely on their camouflage for avoiding predators, but some have conspicuous eyespots and several small tropical species are poisonous. Juveniles of Soleichthys maculosus mimic toxic flatworms of the genus Pseudobiceros in both colours and swimming mode. Conversely, a few octopus species have been reported to mimic flatfishes in colours and swimming mode; the flounders and spiny turbots eat smaller fish, have well-developed teeth. They sometimes seek prey in the midwater, away from the bottom, show fewer extreme adaptations than other families; the soles, by contrast, are exclusively bottom-dwellers, feed on invertebrates. They show a more extreme asymmetry, may lack teeth on one side of the jaw. Flatfishes range in size from Tarphops oligolepis, measuring about 4.5 cm in length, weighing 2 g, to the Atlantic halibut, at 2.5 m and 316 kg. Flatfishes lay eggs that hatch into larvae resembling typical, fish.
These are elongated, but develop into a more rounded form. The larvae have protective spines on the head, over the gills, in the pelvic and pectoral fins, they possess a swim bladder, do not dwell on the bottom, instead dispersing from their hatching grounds as plankton. The length of the planktonic stage varies between different types of flatfishes, but they begin to metamorphose into the adult form. One of the eyes migrates across the top of the head and onto the other side of the body, leaving the fish blind on one side; the larva loses its swim bladder and spines, sinks to the bottom, laying its blind side on the underlying surface. In 2008, a 50-million-year-old fossil, was identified as an early relative of the flatfish and transitional fossil. In a typical modern flatfish, the head is asymmetric, with both eyes on one side of the head. In Amphistium, the transition from the typica
The gastropod shell is part of the body of a gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, dehydration, but serves for muscle attachment and calcium storage; some gastropods appear shell-less but may have a remnant within the mantle, or the shell is reduced such that the body cannot be retracted within. Some snails possess an operculum that seals the opening of the shell, known as the aperture, which provides further protection; the study of mollusc shells is known as conchology. The biological study of gastropods, other molluscs in general, is malacology. Shell morphology terms vary by species group. An excellent source for terminology of the gastropod shell is "How to Know the Eastern Land Snails" by John B. Burch now available at the Hathi Trust Digital Library; the gastropod shell has three major layers secreted by the mantle. The calcareous central layer, tracum, is made of calcium carbonate precipitated into an organic matrix known as conchiolin.
The outermost layer is the periostracum, resistant to abrasion and provides most shell coloration. The body of the snail contacts the innermost smooth layer that may be composed of mother-of-pearl or shell nacre, a dense horizontally packed form of conchiolin, layered upon the periostracum as the snail grows. Gastropod shell morphology is quite constant among individuals of a species. Controlling variables are: The rate of growth per revolution around the coiling axis. High rates give wide-mouthed forms such as the abalone, low rates give coiled forms such as Turritella or some of the Planorbidae; the shape of the generating curve equivalent to the shape of the aperture. It may be round, for instance in the turban shell, elongate as in the cone shell or have an irregular shape with a siphonal canal extension, as in the Murex; the rate of translation of the generating curve along the axis of coiling, controlling how high-spired the resulting shell becomes. This may range from a flat planispiral shell, to nearly the diameter of the aperture.
Irregularities or "sculpturing" such as ribs, spines and varices made by the snail changing the shape of the generating curve during the course of growth, for instance in the many species of Murex. Ontologic growth changes as the animal reaches adulthood. Good examples are the inward-coiled lip of the cowry; some of these factors can be modelled mathematically and programs exist to generate realistic images. Early work by David Raup on the analog computer revealed many possible combinations that were never adopted by any actual gastropod; some shell shapes are found more in certain environments, though there are many exceptions. Wave-washed high-energy environments, such as the rocky intertidal zone, are inhabited by snails whose shells have a wide aperture, a low surface area, a high growth rate per revolution. High-spired and sculptured forms become more common in quiet water environments; the shell of burrowing forms, such as the olive and Terebra, are smooth and lack elaborate sculpture, in order to decrease resistance when moving through sand.
On land, high-spired forms are associated with vertical surfaces, whereas flat-shelled snails tend to live on the ground. A few gastropods, for instance the Vermetidae, cement the shell to, grow along, solid surfaces such as rocks, or other shells. Most gastropod shells are spirally coiled; the majority of gastropod species have dextral shells, but a small minority of species and genera are always sinistral, a few species show a mixture of dextral and sinistral individuals. There occur aberrantly sinistral forms of dextral species and some of these are sought by shell collectors. If a coiled gastropod shell is held with the spire pointing upwards and the aperture more or less facing the observer, a dextral shell will have the aperture on the right-hand side, a sinistral shell will have the aperture on the left-hand side; this chirality of gastropods is sometimes overlooked when photographs of coiled gastropods are "flipped" by a non-expert prior to being used in a publication. This image "flipping" results in a normal dextral gastropod appearing to be a rare or abnormal sinistral one.
Sinistrality arose independently 19 times among marine gastropods since the start of the Cenozoic. This left-handedness seems to be more common in land pulmonates, but still the dextral living species in gastropods seem to account for 99% of the total number. The chirality in gastropods appears in the gene NODAL is involved. A more recent study correlates the asymmetric coiling of the shell by the left-right asymmetric expression of the decapentaplegic gene in the mantle. In a few cases, both left- and right-handed coiling are found in the same population. Sinistral mutants of dextral species and dextral mutants of sinistral species are rare but well documented occurrences among land snails in general. Populations or species with mixed coiling are much rarer, and, so far as is known, are confined, with one exception, to a few genera of arboreal tropical snails. Besides Amphidromus, the Cuban Liguus vittatus, Haitian Liguus virgineus, some Hawaiian Partulina and many Hawaiian Achatinella, as well as several species of Pacific islands Partula, are known to have mixed dextral-sinistral populations.
A possible exception may concern some of the European clausiliids of the subfamily Alopiinae. They are ob
Dexter and sinister
Dexter and sinister are terms used in heraldry to refer to specific locations in an escutcheon bearing a coat of arms, to the other elements of an achievement. "Dexter" means to the right from the viewpoint of the bearer of the shield, i.e. the bearer's proper right, to the left from that of the viewer. "Sinister" means to the left from the viewpoint of the bearer, the bearer's proper left, to the right from that of the viewer. The dexter side is considered the side of greater honour, for example. Thus, by tradition, a husband's arms occupy the dexter half of his shield, his wife's paternal arms the sinister half; the shield of a bishop shows the arms of his see in the dexter half, his personal arms in the sinister half. King Richard II adopted arms showing the attributed arms of Edward the Confessor in the dexter half, the royal arms of England in the sinister. More by ancient tradition, the guest of greatest honour at a banquet sits at the right hand of the host; the Bible is replete with passages referring to being at the "right hand" of God.
Sinister is used to mark that an ordinary or other charge is turned to the heraldic left of the shield. A bend sinister is a bend which runs from the bearer's top left to bottom right, as opposed to top right to bottom left; as the shield would have been carried with the design facing outwards from the bearer, the bend sinister would slant in the same direction as a sash worn diagonally on the left shoulder. This division is key to dimidiation, a method of joining two coats of arms by placing the dexter half of one coat of arms alongside the sinister half of the other. In the case of marriage, the dexter half of the husband's arms would be placed alongside the sinister half of the wife's; the practice fell out of use as early as the 14th century and was replaced by impalement, as in some cases, it could render the arms that are cut in half unrecognizable and in some cases, it would result in a shield that looked like one coat of arms rather than a combination of two. The Great Seal of the United States features an eagle clutching an olive branch in its dexter talon and arrows in its sinister talon, indicating the nation's intended inclination to peace.
In 1945, one of the changes ordered for the arranged Flag of the President of the United States by President Harry S. Truman was having the eagle face towards its right and thus towards the olive branch; the sides of a shield were named for the purpose of military training of knights and soldiers long before heraldry came into use early in the 13th century so the only viewpoint, relevant was the bearer's. The front of the purely-functional shield was undecorated, it is that the use of the shield as a defensive and offensive weapon was as developed as that of the sword itself and so the various positions or strokes of the shield needed to be described to students of arms. Such usage may indeed have descended directly from Roman training techniques that were spread throughout Roman Europe and continued during the age of chivalry, when heraldry came into use
Anatomical terms of location
Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. All vertebrates have the same basic body plan – they are bilaterally symmetrical in early embryonic stages and bilaterally symmetrical in adulthood; that is, they have mirror-image left and right halves if divided down the middle. For these reasons, the basic directional terms can be considered to be those used in vertebrates. By extension, the same terms are used for many other organisms as well. While these terms are standardized within specific fields of biology, there are unavoidable, sometimes dramatic, differences between some disciplines. 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. Standardized anatomical and zoological terms of location have been developed based on Latin and Greek words, to enable all biological and medical scientists to delineate and communicate information about animal bodies and their component organs though the meaning of some of the terms is context-sensitive.
The vertebrates and Craniata share a substantial heritage and common structure, so many of the same terms are used for location. 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. For one reason, this is because humans have a different neuraxis and, unlike animals that rest on four limbs, humans are considered when describing anatomy as being in the standard anatomical position, thus what is on "top" of a human is the head, whereas the "top" of a dog may be its back, the "top" of a flounder could refer to either its left or its right side. For invertebrates, standard application of locational terminology becomes difficult or debatable at best when the differences in morphology are so radical that common concepts are not homologous and do not refer to common concepts. For example, many species are not bilaterally symmetrical. In these species, terminology depends on their type of symmetry.
Because animals can change orientation with respect to their environment, because appendages like limbs and tentacles can change position with respect to the main body, positional descriptive terms need to refer to the animal as in its standard anatomical position. All descriptions are with respect to the organism in its standard anatomical position when the organism in question has appendages in another position; this helps avoid confusion in terminology. In humans, this refers to the body in a standing position with arms at the side and palms facing forward. While the universal vertebrate terminology used in veterinary medicine would work in human medicine, the human terms are thought to be too well established to be worth changing. Many anatomical terms can be combined, either to indicate a position in two axes or to indicate the direction of a movement relative to the body. For example, "anterolateral" indicates a position, both anterior and lateral to the body axis. In radiology, an X-ray image may be said to be "anteroposterior", indicating that the beam of X-rays pass from their source to patient's anterior body wall through the body to exit through posterior body wall.
There is no definite limit to the contexts in which terms may be modified to qualify each other in such combinations. The modifier term is truncated and an "o" or an "i" is added in prefixing it to the qualified term. For example, a view of an animal from an aspect at once dorsal and lateral might be called a "dorsolateral" view. Again, in describing the morphology of an organ or habitus of an animal such as many of the Platyhelminthes, one might speak of it as "dorsiventrally" flattened as opposed to bilaterally flattened animals such as ocean sunfish. Where desirable three or more terms may be agglutinated or concatenated, as in "anteriodorsolateral"; such terms sometimes used to be hyphenated. There is however little basis for any strict rule to interfere with choice of convenience in such usage. Three basic reference planes are used to describe location; the sagittal plane is a plane parallel to the sagittal suture. All other sagittal planes are parallel to it, it is known as a "longitudinal plane".
The plane is perpendicular to the ground. The median plane or midsagittal plane is in the midline of the body, divides the body into left and right portions; this passes through the head, spinal cord, and, in many animals, the tail. The term "median plane" can refer to the midsagittal plane of other structures, such as a digit; the frontal plane or coronal plane divides the body into ventral portions. For post-embryonic humans a coronal plane is vertical and a transverse plane is horizontal, but for embryos and quadrupeds a coronal plane is horizontal and a transverse plane is vertical. A longitudinal plane is any plane perpendicular to the transverse plane; the coronal plane and the sagittal plane are examples of longitudinal planes. A transverse plane known as a cross-section, divides the body into cranial and caudal portions. In human anatomy: A transverse plane is an X-Z plane, parallel to the ground, which s
Heraldry is a broad term, encompassing the design and study of armorial bearings, as well as related disciplines, such as vexillology, together with the study of ceremony and pedigree. Armory, the best-known branch of heraldry, concerns the design and transmission of the heraldic achievement; the achievement, or armorial bearings includes a coat of arms on an shield and crest, together with any accompanying devices, such as supporters, heraldic banners, mottoes. Although the use of various devices to signify individuals and groups goes back to antiquity, both the form and use of such devices varied and the concept of regular, hereditary designs, constituting the distinguishing feature of heraldry, did not develop until the High Middle Ages, it is often that the use of helmets with face guards during this period made it difficult to recognize one's commanders in the field when large armies gathered together for extended periods, necessitating the development of heraldry as a symbolic language but there is little actual support for this view.
The beauty and pageantry of heraldic designs allowed them to survive the gradual abandonment of armour on the battlefield during the seventeenth century. Heraldry has been described poetically as "the handmaid of history", "the shorthand of history", "the floral border in the garden of history". In modern times, individuals and private organizations, cities and regions use heraldry and its conventions to symbolize their heritage and aspirations. Various symbols have been used to represent groups for thousands of years; the earliest representations of distinct persons and regions in Egyptian art show the use of standards topped with the images or symbols of various gods, the names of kings appear upon emblems known as serekhs, representing the king's palace, topped with a falcon representing the god Horus, of whom the king was regarded as the earthly incarnation. Similar emblems and devices are found in ancient Mesopotamian art of the same period, the precursors of heraldic beasts such as the griffin can be found.
In the Bible, the Book of Numbers refers to the standards and ensigns of the children of Israel, who were commanded to gather beneath these emblems and declare their pedigrees. The Greek and Latin writers describe the shields and symbols of various heroes, units of the Roman army were sometimes identified by distinctive markings on their shields; until the nineteenth century, it was common for heraldic writers to cite examples such as these, metaphorical symbols such as the "Lion of Judah" or "Eagle of the Caesars" as evidence of the antiquity of heraldry itself. The Book of Saint Albans, compiled in 1486, declares that Christ himself was a gentleman of coat armour, but these fabulous claims have long since been dismissed as the fantasy of medieval heralds, for there is no evidence of a distinctive symbolic language akin to that of heraldry during this early period. The medieval heralds devised arms for various knights and lords from history and literature. Notable examples include the toads attributed to Pharamond, the cross and martlets of Edward the Confessor, the various arms attributed to the Nine Worthies and the Knights of the Round Table.
These too are now regarded as a fanciful invention, rather than evidence of the antiquity of heraldry. The development of the modern heraldic language cannot be attributed to a single individual, time, or place. Although certain designs that are now considered heraldic were evidently in use during the eleventh century, most accounts and depictions of shields up to the beginning of the twelfth century contain little or no evidence of their heraldic character. For example, the Bayeux Tapestry, illustrating the Norman invasion of England in 1066, commissioned about 1077, when the cathedral of Bayeux was rebuilt, depicts a number of shields of various shapes and designs, many of which are plain, while others are decorated with dragons, crosses, or other heraldic figures, yet no individual is depicted twice bearing the same arms, nor are any of the descendants of the various persons depicted known to have borne devices resembling those in the tapestry. An account of the French knights at the court of the Byzantine emperor Alexius I at the beginning of the twelfth century describes their shields of polished metal, utterly devoid of heraldic design.
A Spanish manuscript from 1109 describes both plain and decorated shields, none of which appears to have been heraldic. The Abbey of St. Denis contained a window commemorating the knights who embarked on the Second Crusade in 1147, was made soon after the event. In England, from the time of the Norman conquest, official documents had to be sealed. Beginning in the twelfth century, seals assumed a distinctly heraldic character. A notable example of an early armorial seal is attached to a charter granted by Philip I, Count of Flanders, in 1164. Seals from the latter part of the eleventh and early twelfth centuries show no evidence of heraldic symbolism, but by t
Chirality is a property of asymmetry important in several branches of science. The word chirality is derived from "hand," a familiar chiral object. An object or a system is chiral. Conversely, a mirror image of an achiral object, such as a sphere, cannot be distinguished from the object. A chiral object and its mirror image are called enantiomorphs or, when referring to molecules, enantiomers. A non-chiral object can be superposed on its mirror image. If the object is non-chiral and is imagined as being colored blue and its mirror image is imagined as colored yellow by a series of rotations and translations the two can be superposed, producing green, with none of the original colors remaining; the term was first used by Lord Kelvin in 1893 in the second Robert Boyle Lecture at the Oxford University Junior Scientific Club, published in 1894: I call any geometrical figure, or group of points,'chiral', say that it has chirality if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself.
Human hands are the most universally recognized example of chirality. The left hand is a non-superimposable mirror image of the right hand; this difference in symmetry becomes obvious if someone attempts to shake the right hand of a person using their left hand, or if a left-handed glove is placed on a right hand. In mathematics, chirality is the property of a figure, not identical to its mirror image. In mathematics, a figure is chiral if it cannot be mapped to its mirror image by rotations and translations alone. For example, a right shoe is different from a left shoe, clockwise is different from anticlockwise. See for a full mathematical definition. A chiral object and its mirror image are said to be enantiomorphs; the word enantiomorph stems from the Greek ἐναντίος'opposite' + μορφή'form'. A non-chiral figure is called amphichiral; the helix and Möbius strip are chiral two-dimensional objects in three-dimensional ambient space. The J, L, S and Z-shaped tetrominoes of the popular video game Tetris exhibit chirality, but only in a two-dimensional space.
Many other familiar objects exhibit the same chiral symmetry of the human body, such as gloves and shoes. A similar notion of chirality is considered in knot theory; some chiral three-dimensional objects, such as the helix, can be assigned a right or left handedness, according to the right-hand rule. In geometry a figure is achiral if and only if its symmetry group contains at least one orientation-reversing isometry. In two dimensions, every figure that possesses an axis of symmetry is achiral, it can be shown that every bounded achiral figure must have an axis of symmetry. In three dimensions, every figure that possesses a plane of symmetry or a center of symmetry is achiral. There are, achiral figures lacking both plane and center of symmetry. In terms of point groups, all chiral figures lack an improper axis of rotation; this means that they can not contain a center of a mirror plane. Only figures with a point group designation of C1, Cn, Dn, T, O, or I can be chiral. A knot is called achiral if it can be continuously deformed into its mirror image, otherwise it is called chiral.
For example, the unknot and the figure-eight knot are achiral. In physics, chirality may be found in the spin of a particle, where the handedness of the object is determined by the direction in which the particle spins. Not to be confused with helicity, the projection of the spin along the linear momentum of a subatomic particle, chirality is a purely quantum mechanical phenomenon like spin. Although both can have left-handed or right-handed properties, only in the massless case do they have a simple relation. In particular for a massless particle the helicity is the same as the chirality while for an antiparticle they have opposite sign; the handedness in both chirality and helicity relate to the rotation of a particle while it proceeds in linear motion with reference to the human hands. The thumb of the hand points towards the direction of linear motion whilst the fingers curl into the palm, representing the direction of rotation of the particle. Depending on the linear and rotational motion, the particle can either be defined by left-handedness or right-handedness.
A symmetry transformation between the two is called parity. Invariance under parity by a Dirac fermion is called chiral symmetry. Electromagnetic wave propagation as handedness is wave polarization and described in terms of helicity. Polarization of an electromagnetic wave is the property that describes the orientation, i.e. the time-varying and amplitude of the electric field vector. For a depiction, see the adjacent image. A chiral molecule is a type of molecule; the feature, most the cause of chirality in molecules is the presence of an asymmetric carbon atom. The term "chiral" in general is used to describe the object, non-superposable on its mirror image. In chemistry, chirality refers to molecules. Two mirror images of a chiral molecule are called enantiomers or optical isomers