Crabs are decapod crustaceans of the infraorder Brachyura, which have a short projecting "tail" entirely hidden under the thorax. They live in all the world's oceans, in fresh water, on land, are covered with a thick exoskeleton and have a single pair of pincers. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, crab lice – are not true crabs. Crabs are covered with a thick exoskeleton, composed of mineralized chitin, armed with a single pair of chelae. Crabs are found in all of the world's oceans, while many crabs live in fresh water and on land in tropical regions. Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 metres. About 850 species of crab are terrestrial or semi-terrestrial species, they were thought to be a monophyletic group, but are now believed to represent at least two distinct lineages, one in the Old World and one in the New World. The earliest unambiguous crab fossils date from the Jurassic, although Carboniferous Imocaris, known only from its carapace, may be a primitive crab.
The radiation of crabs in the Cretaceous and afterward may be linked either to the break-up of Gondwana or to the concurrent radiation of bony fish, crabs' main predators. Crabs show marked sexual dimorphism. Males have larger claws, a tendency, pronounced in the fiddler crabs of the genus Uca. In fiddler crabs, males have one claw, enlarged and, used for communication for attracting a mate. Another conspicuous difference is the form of the pleon; this is. Crabs attract a mate through chemical, acoustic, or vibratory means. Pheromones are used by most aquatic crabs, while terrestrial and semiterrestrial crabs use visual signals, such as fiddler crab males waving their large claws to attract females; the vast number of brachyuran crabs have mate belly-to-belly. For many aquatic species, mating takes place just after the female is still soft. Females can store the sperm for a long time before using it to fertilise their eggs; when fertilisation has taken place, the eggs are released onto the female's abdomen, below the tail flap, secured with a sticky material.
In this location, they are protected during embryonic development. Females carrying eggs are called "berried"; when development is complete, the female releases the newly hatched larvae into the water, where they are part of the plankton. The release is timed with the tides; the free-swimming tiny zoea larvae can take advantage of water currents. They have a spine, which reduces the rate of predation by larger animals; the zoea of most species must find food, but some crabs provide enough yolk in the eggs that the larval stages can continue to live off the yolk. Each species has a particular number of zoeal stages, separated by moults, before they change into a megalopa stage, which resembles an adult crab, except for having the abdomen sticking out behind. After one more moult, the crab is a juvenile, living on the bottom rather than floating in the water; this last moult, from megalopa to juvenile, is critical, it must take place in a habitat, suitable for the juvenile to survive. Most species of terrestrial crabs must migrate down to the ocean to release their larvae.
After living for a short time as larvae in the ocean, the juveniles must do this migration in reverse. In many tropical areas with land crabs, these migrations result in considerable roadkill of migrating crabs. Once crabs have become juveniles, they will still have to keep moulting many more times to become adults, they are covered with a hard shell. The moult cycle is coordinated by hormones; when preparing for moult, the old shell is softened and eroded away, while the rudimentary beginnings of a new shell form under it. At the time of moulting, the crab takes in a lot of water to expand and crack open the old shell at a line of weakness along the back edge of the carapace; the crab must extract all of itself – including its legs, mouthparts and the lining of the front and back of the digestive tract – from the old shell. This is a difficult process that takes many hours, if a crab gets stuck, it will die. After freeing itself from the old shell, the crab is soft and hides until its new shell has hardened.
While the new shell is still soft, the crab can expand it to make room for future growth. Crabs walk sideways, because of the articulation of the legs which makes a sidelong gait more efficient. However, some crabs walk forwards or backwards, including raninids, Libinia emarginata and Mictyris platycheles; some crabs, notably the Portunidae and Matutidae, are capable of swimming, the Portunidae so as their last pair of walking legs is flattened into swimming paddles. Crabs are active animals with complex behaviour patterns, they can communicate by waving their pincers. Crabs tend to be aggressive towards one another, males fight to gain access to females. On rocky seashores, where nearly all caves and crevices
Diatoms are a major group of algae microalgae, found in the oceans and soils of the world. Living diatoms number in the trillions: they generate about 20 percent of the oxygen produced on the planet each year, take in over 6.7 billion metric tons of silicon each year from the waters in which they live, contribute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half mile deep on the ocean floor, the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by east-to-west transatlantic winds from the bed of a dried up lake once covering much of the African Sahara. Diatoms are unicellular: they occur either as solitary cells or in colonies, which can take the shape of ribbons, zigzags, or stars. Individual cells range in size from 2 to 200 micrometers. In the presence of adequate nutrients and sunlight, an assemblage of living diatoms doubles every 24 hours by asexual multiple fission. Diatoms have two distinct shapes: a few are radially symmetric, while most are broadly bilaterally symmetric.
A unique feature of diatom anatomy is that they are surrounded by a cell wall made of silica, called a frustule. These frustules have structural coloration due to their photonic nanostructure, prompting them to be described as "jewels of the sea" and "living opals". Movement in diatoms occurs passively as a result of both water currents and wind-induced water turbulence. Similar to plants, diatoms convert light energy to chemical energy by photosynthesis, although this shared autotrophy evolved independently in both lineages. Unusually for autotrophic organisms, diatoms possess a urea cycle, a feature that they share with animals, although this cycle is used to different metabolic ends in diatoms; the study of diatoms is a branch of phycology. Diatoms are classified as eukaryotes, organisms with a membrane-bound cell nucleus, that separates them from the prokaryotes archaea and bacteria. Diatoms are a type of plankton called phytoplankton, the most common of the plankton types. Diatoms grow attached to benthic substrates, floating debris, on macrophytes.
They comprise an integral component of the periphyton community. Another classification divides plankton into eight types based on size: in this scheme, diatoms are classed as microalgae. Several systems for classifying the individual diatom species exist. Fossil evidence suggests that diatoms originated during or before the early Jurassic period, about 150 to 200 million years ago. Diatoms are used to monitor past and present environmental conditions, are used in studies of water quality. Diatomaceous earth is a collection of diatom shells found in the earth's crust, they are soft, silica-containing sedimentary rocks which are crumbled into a fine powder and have a particle size of 10 to 200 μm. Diatomaceous earth is used for a variety of purposes including for water filtration, as a mild abrasive, in cat litter, as a dynamite stabilizer. Diatoms are 2 to 200 micrometers in length, their yellowish-brown chloroplasts, the site of photosynthesis, are typical of heterokonts, having four membranes and containing pigments such as the carotenoid fucoxanthin.
Individuals lack flagella, but they are present in male gametes of the centric diatoms and have the usual heterokont structure, except they lack the hairs characteristic in other groups. Diatoms are referred as "jewels of the sea" or "living opals" due to their photonic crystal properties; the biological function of this structural coloration is not clear, but it is speculated that it may be related to communication, thermal exchange and/or UV protection. Diatoms build intricate hard but porous cell walls called frustules composed of silica; this siliceous wall can be patterned with a variety of pores, minute spines, marginal ridges and elevations. The cell itself consists of two halves, each containing an flat plate, or valve and marginal connecting, or girdle band. One half, the hypotheca, is smaller than the other half, the epitheca. Diatom morphology varies. Although the shape of the cell is circular, some cells may be triangular, square, or elliptical, their distinguishing feature is a hard mineral frustule composed of opal.
Most diatoms are nonmotile, as their dense cell walls cause them to sink. Planktonic forms in open water rely on turbulent mixing of the upper layers of the oceanic waters by the wind to keep them suspended in sunlit surface waters; the only mechanism for regulating buoyancy is an ionic pump. Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures. Diatoms are photosynthetic. Diatom cells are contained within a unique silica cell wall known as a frustule made up of two valves called thecae, that overlap one another; the biogenic silica composing the cell wall is synthesised intracellularly by the polymerisation of silicic acid monomer
The mollusc shell is a calcareous exoskeleton which encloses and protects the soft parts of an animal in the phylum Mollusca, which includes snails, tusk shells, several other classes. Not all shelled; the ancestral mollusc is thought to have had a shell, but this has subsequently been lost or reduced on some families, such as the squid and some smaller groups such as the caudofoveata and solenogastres, the derived Xenoturbella. Today, over 100,000 living species bear a shell. Malacology, the scientific study of molluscs as living organisms, has a branch devoted to the study of shells, this is called conchology—although these terms used to be, to a minor extent still are, used interchangeably by scientists. Within some species of molluscs, there is a wide degree of variation in the exact shape, pattern and color of the shell. A mollusc shell is formed and maintained by a part of the anatomy called the mantle. Any injuries to or abnormal conditions of the mantle are reflected in the shape and form and color of the shell.
When the animal encounters harsh conditions that limit its food supply, or otherwise cause it to become dormant for a while, the mantle ceases to produce the shell substance. When conditions improve again and the mantle resumes its task, a "growth line" is produced; the mantle edge secretes a shell. The organic constituent is made up of polysaccharides and glycoproteins; this organic framework controls the formation of calcium carbonate crystals, dictates when and where crystals start and stop growing, how fast they expand. The shell formation requires certain biological machinery; the shell is deposited within a small compartment, the extrapallial space, sealed from the environment by the periostracum, a leathery outer layer around the rim of the shell, where growth occurs. This caps off the extrapallial space, bounded on its other surfaces by the existing shell and the mantle; the periostracum acts as a framework from which the outer layer of carbonate can be suspended, but in sealing the compartment, allows the accumulation of ions in concentrations sufficient for crystallization to occur.
The accumulation of ions is driven by ion pumps packed within the calcifying epithelium. Calcium ions are obtained from the organism's environment through the gills and epithelium, transported by the haemolymph to the calcifying epithelium, stored as granules within or in-between cells ready to be dissolved and pumped into the extrapallial space when they are required; the organic matrix forms the scaffold that directs crystallization, the deposition and rate of crystals is controlled by hormones produced by the mollusc. Because the extrapallial space is supersaturated, the matrix could be thought of as impeding, rather than encouraging, carbonate deposition. Nucleation is endoepithelial in Neopilina and Nautilus, but exoepithelial in the bivalves and gastropods; the formation of the shell involves a number of genes and transcription factors. On the whole, the transcription factors and signalling genes are conserved, but the proteins in the secretome are derived and evolving. Engrailed serves to demark the edge of the shell field.
In gastropod embryos, Hox1 is expressed. Perlucin increases the rate at which calcium carbonate precipitates to form a shell when in saturated seawater. Perlucin operates in association with Perlustrin, a smaller relative of lustrin A, a protein responsible for the elasticity of organic layers that makes nacre so resistant to cracking. Lustrin A bears remarkable structural similarity to the proteins involved in mineralization in diatoms – though diatoms use silica, not calcite, to form their tests! The shell-secreting area is differentiated early in embryonic development. An area of the ectoderm thickens invaginates to become a "shell gland"; the shape of this gland is tied to the form of the adult shell. The gland subsequently evaginates in molluscs. Whilst invaginated, a periostracum - which will form a scaffold for the developing shell - is formed around the opening of the invagination, allowing the deposition of the shell when the gland
Foraminifera are members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses. Tests of chitin are believed to be the most primitive type. Most foraminifera are marine, the majority of which live on or within the seafloor sediment, while a smaller variety float in the water column at various depths. Fewer are known from freshwater or brackish conditions, some few soil species have been identified through molecular analysis of small subunit ribosomal DNA. Foraminifera produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure; these shells are made of calcium carbonate or agglutinated sediment particles. Over 50,000 species are recognized, both fossil, they are less than 1 mm in size, but some are much larger, the largest species reaching up to 20 cm. In modern Scientific English, the term foraminifera is both singular and plural, is used to describe one or more specimens or taxa: its usage as singular or plural must be determined from context.
Foraminifera is used informally to describe the group, in these cases is lowercase. The taxonomic position of the Foraminifera has varied since their recognition as protozoa by Schultze in 1854, there referred to as an order, Foraminiferida. Loeblich and Tappan reranked Foraminifera as a class as it is now regarded; the Foraminifera have been included in the Protozoa, or in the similar Protoctista or Protist kingdom. Compelling evidence, based on molecular phylogenetics, exists for their belonging to a major group within the Protozoa known as the Rhizaria. Prior to the recognition of evolutionary relationships among the members of the Rhizaria, the Foraminifera were grouped with other amoeboids as phylum Rhizopodea in the class Granuloreticulosa; the Rhizaria are problematic, as they are called a "supergroup", rather than using an established taxonomic rank such as phylum. Cavalier-Smith defines the Rhizaria as an infra-kingdom within the kingdom Protozoa; some taxonomies put the Foraminifera in a phylum of their own, putting them on par with the amoeboid Sarcodina in which they had been placed.
Although as yet unsupported by morphological correlates, molecular data suggest the Foraminifera are related to the Cercozoa and Radiolaria, both of which include amoeboids with complex shells. However, the exact relationships of the forams to the other groups and to one another are still not clear. Foraminifera are related to testate amoebae; the most recent taxonomy by Mikhalevich 2013. Foraminifera d'Orbigny 1826 Order Reticulomyxida Class Schizocladea Cedhagen & Mattson 1992 Order Schizocladida Class Xenophyophorea Schultze 1904 Order Stannomida Tendal 1972 Order Psamminida Tendal 1972 Class Astrorhizata Saidova 1981 Subclass Lagynana Mikhalevich 1980 Order Ammoscalariida Mikhalevich 1980 Order Lagynida Mikhalevich 1980 Order Allogromiida Loeblich & Tappan 1961 Subclass Astrorhizana Saidova 1981 Order Astrorhizida Lankester 1885 Order Dendrophryida Mikhalevich 1995 Order Hippocrepinida Saidova 1981 Order †Parathuramminida Mikhalevich 1980 Order Psammosphaerida Haeckel 1894 Class Rotaliata Mikhalevich 1980 Subclass Globigerinana Mikhalevich 1980 Order Cassigerinellida Mikhalevich 2013 Order Globigerinida Carpenter, Parker & Jones 1862 Order Hantkeninida Mikhalevich 1980 Order Heterohelicida Fursenko 1958 Order Globorotaliida Mikhalevich 1980 Subclass Textulariana Mikhalevich 1980 Order Nautiloculinida Mikhalevich 2003 Order Spiroplectamminida Mikhalevich 1992 Order Textulariida Delage & Hérouard 1896 Order Trochamminida Saidova 1981 (Carterinida Loeblich & Tappan 1955] Order Verneuilinida Mikhalevich & Kaminski 2003 Subclass Rotaliana Mikhalevich 1980 Superorder Robertinoida Mikhalevich 1980 Order Robertinida Mikhalevich 1980 Superorder Nonionoida Saidova 1981 Order Elphidiida Saidova 1981 Order Nummulitida Carpenter, Parker & Jones 1862 Order †Orbitoidida Copeland 1956 Order Nonionida Saidova 1981 Superorder Buliminoida Saidova 1981 Order Cassidulinida d’Orbigny 1839 Order Buliminida Saidova 1981 Order Bolivinitida Saidova 1981 Superorder Discorboida Ehrenberg 1838 Order Chilostomellida Haeckel 1894 Order Discorbida Ehrenberg 1838 Order Glabratellida Mikhalevich 1994 Order Planorbulinida Mikhalevich 1992 Order Rotaliida Lankester 1885 Order Rosalinida Delage & Hérouard 1896 Class Nodosariata Mikhalevich 1992 Subclass Hormosinana Mikhalevich 1992 Order Ammomarginulinida Mikhalevich 2002 Order Nouriida Mikhalevich 1980 Order †Pseudopalmulida Mikhalevich 1992 Order Saccamminida Lankester 1885 Order Hormosinida Mikhalevich 1980 Subclass Nodosariana Mikhalevich 1992 Order †Biseriamminida Mikhalevich 1981 Order Delosinida Revets 1989 Order Lagenida Delage & Hérouard 1896 Order †Palaeotextulariida Hohenegger & Piller 1975 Order Polymorphinida Mikhalevich 1980 Order Vaginulinida Mikhalevich 1993 Order Nodosariida Calkins 1926 Class Spirillinata Mikhalevich 1992 Subclass Ammodiscana Mikhalevich 1980 Order †Plagioraphida Mikhalevich 2003 Order Ammodiscida Mikhalevich 1980 Order Ammovertellinida Mikhalevich 1999 Order Ataxophragmiida Fursenko 1958 Subclass Spirillinana Mikhalevich 1992 Superorder †Archaediscoida Pojarkov & Skvortsov 1979 Order †Archaediscida Pojarkov & Skvortsov 1979 Order †Lasiodiscida
The mineral pyrite, or iron pyrite known as fool's gold, is an iron sulfide with the chemical formula FeS2. Pyrite is considered the most common of the sulfide minerals. Pyrite's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold; the color has led to the nicknames brass and Brazil used to refer to pyrite found in coal. The name pyrite is derived from the Greek πυρίτης, "of fire" or "in fire", in turn from πύρ, "fire". In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel. By Georgius Agricola's time, c. 1550, the term had become a generic term for all of the sulfide minerals. Pyrite is found associated with other sulfides or oxides in quartz veins, sedimentary rock, metamorphic rock, as well as in coal beds and as a replacement mineral in fossils, but has been identified in the sclerites of scaly-foot gastropods. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold.
Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37% gold by weight. Pyrite enjoyed brief popularity in the 16th and 17th centuries as a source of ignition in early firearms, most notably the wheellock, where a sample of pyrite was placed against a circular file to strike the sparks needed to fire the gun. Pyrite has been used since classical times to manufacture copperas. Iron pyrite was allowed to weather; the acidic runoff from the heap was boiled with iron to produce iron sulfate. In the 15th century, new methods of such leaching began to replace the burning of sulfur as a source of sulfuric acid. By the 19th century, it had become the dominant method. Pyrite remains in commercial use for the production of sulfur dioxide, for use in such applications as the paper industry, in the manufacture of sulfuric acid. Thermal decomposition of pyrite into FeS and elemental sulfur starts at 540 °C. A newer commercial use for pyrite is as the cathode material in Energizer brand non-rechargeable lithium batteries.
Pyrite is a semiconductor material with a band gap of 0.95 eV. Pure pyrite is n-type, in both crystal and thin-film forms due to sulfur vacancies in the pyrite crystal structure acting as n-dopants. During the early years of the 20th century, pyrite was used as a mineral detector in radio receivers, is still used by crystal radio hobbyists; until the vacuum tube matured, the crystal detector was the most sensitive and dependable detector available – with considerable variation between mineral types and individual samples within a particular type of mineral. Pyrite detectors occupied a midway point between galena detectors and the more mechanically complicated perikon mineral pairs. Pyrite detectors can be as sensitive as a modern 1N34A germanium diode detector. Pyrite has been proposed as an abundant, non-toxic, inexpensive material in low-cost photovoltaic solar panels. Synthetic iron sulfide was used with copper sulfide to create the photovoltaic material.. More recent efforts are working toward thin-film solar cells made of pyrite.
Pyrite is used to make marcasite jewelry. Marcasite jewelry, made from small faceted pieces of pyrite set in silver, was known since ancient times and was popular in the Victorian era. At the time when the term became common in jewelry making, "marcasite" referred to all iron sulfides including pyrite, not to the orthorhombic FeS2 mineral marcasite, lighter in color and chemically unstable, thus not suitable for jewelry making. Marcasite jewelry does not contain the mineral marcasite. China represents the main importing country with an import of around 376,000 tonnes, which resulted at 45% of total global imports. China is the fastest growing in terms of the unroasted iron pyrites imports, with a CAGR of +27.8% from 2007 to 2016. In value terms, China constitutes the largest market for imported unroasted iron pyrites worldwide, making up 65% of global imports. From the perspective of classical inorganic chemistry, which assigns formal oxidation states to each atom, pyrite is best described as Fe2+S22−.
This formalism recognizes. These persulfide units can be viewed as derived from hydrogen disulfide, H2S2, thus pyrite would be more descriptively, not iron disulfide. In contrast, molybdenite, MoS2, features isolated sulfide centers and the oxidation state of molybdenum is Mo4+; the mineral arsenopyrite has the formula FeAsS. Whereas pyrite has S2 subunits, arsenopyrite has units, formally derived from deprotonation of H2AsSH. Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe3+3−. Iron-pyrite FeS2 represents the prototype compound of the crystallographic pyrite structure; the structure is simple cubic and was among the first crystal structures solved by X-ray diffraction. It belongs to the crystallographic space group Pa3 and is denoted by the Strukturbericht notation C2. Under thermodynamic standard conditions the lattice constant a of stoichiometric iron pyrite FeS2 amounts to 541.87 pm. The unit cell is composed of a Fe face-centered cubic sublattice into.
The pyrite structure is used by other compounds MX2 of trans
Tortoises are reptile species of the family Testudinidae of the order Testudines. They are distinguished from other turtles by being land-dwelling, while many other turtle species are at least aquatic. However, like other turtles, tortoises have a shell to protect from other threats; the shell in tortoises is hard, like other members of the suborder Cryptodira, they retract their necks and heads directly backwards into the shell to protect them. Tortoises are unique among vertebrates in that the pectoral and pelvic girdles are inside the ribcage rather than outside. Tortoises can vary in dimension from a few centimeters to two meters, they are diurnal animals with tendencies to be crepuscular depending on the ambient temperatures. They are reclusive animals. Tortoises are the longest living land animal in the world, although the longest living species of tortoise is a matter of debate. Galápagos tortoises are noted to live over 150 years, but an Aldabra giant tortoise named Adwaita may have been the longest living at an estimated 255 years.
In general, most tortoise species can live 80–150 years. Differences exist in usage of the common terms turtle and terrapin, depending on the variety of English being used; these terms do not reflect precise biological or taxonomic distinctions. The American Society of Ichthyologists and Herpetologists uses "turtle" to describe all species of the order Testudines, regardless of whether they are land-dwelling or sea-dwelling, uses "tortoise" as a more specific term for slow-moving terrestrial species. General American usage agrees. In America, for example, the members of the genus Terrapene dwell on land, yet are referred to as box turtles rather than tortoises. British usage, by contrast, tends not to use "turtle" as a generic term for all members of the order, applies the term "tortoises" broadly to all land-dwelling members of the order Testudines, regardless of whether they are members of the family Testudinidae. In Britain, terrapin is used to refer to a larger group of semiaquatic turtles than the restricted meaning in America.
Australian usage is different from both British usage. Land tortoises are not native to Australia, yet traditionally freshwater turtles have been called "tortoises" in Australia; some Australian experts disapprove of this usage—believing that the term tortoises is "better confined to purely terrestrial animals with different habits and needs, none of which are found in this country"—and promote the use of the term "freshwater turtle" to describe Australia's aquatic members of the order Testudines because it avoids misleading use of the word "tortoise" and is a useful distinction from marine turtles. Most species of tortoises lay small clutch sizes exceeding 20 eggs, many species have clutch sizes of only 1–2 eggs. Incubation is characteristically long in most species, the average incubation period are between 100 and 160 days. Egg-laying occurs at night, after which the mother tortoise covers her clutch with sand and organic material; the eggs are left unattended, depending on the species, take from 60 to 120 days to incubate.
The size of the egg depends on the size of the mother and can be estimated by examining the width of the cloacal opening between the carapace and plastron. The plastron of a female tortoise has a noticeable V-shaped notch below the tail which facilitates passing the eggs. Upon completion of the incubation period, a formed hatchling uses an egg tooth to break out of its shell, it begins a life of survival on its own. They are hatched with an embryonic egg sac which serves as a source of nutrition for the first three to seven days until they have the strength and mobility to find food. Juvenile tortoises require a different balance of nutrients than adults, so may eat foods which a more mature tortoise would not. For example, the young of a herbivorous species will consume worms or insect larvae for additional protein; the number of concentric rings on the carapace, much like the cross-section of a tree, can sometimes give a clue to how old the animal is, since the growth depends on the accessibility of food and water, a tortoise that has access to plenty of forage with no seasonal variation will have no noticeable rings.
Moreover, some tortoises grow more than one ring per season, in some others, due to wear, some rings are no longer visible. Tortoises have one of the longest lifespans of any animal, some individuals are known to have lived longer than 150 years; because of this, they symbolize longevity in some cultures, such as China. The oldest tortoise recorded, one of the oldest individual animals recorded, was Tu'i Malila, presented to the Tongan royal family by the British explorer Captain Cook shortly after its birth in 1777. Tu'i Malila remained in the care of the Tongan royal family until its death by natural causes on May 19, 1965, at the age of 188; the record for the longest-lived vertebrate is exceeded only by one other, a koi named Hanako whose death on July 17, 1977, ended a 226-year lifespan. The Alipore Zoo in India was the home to Adwaita, which zoo officials claimed was the oldest living animal until
A horn is a permanent pointed projection on the head of various animals consisting of a covering of keratin and other proteins surrounding a core of live bone. Horns are distinct from antlers. In mammals, true horns are found among the ruminant artiodactyls, in the families Antilocapridae and Bovidae. One pair of horns is usual. Polycerate sheep breeds include the Hebridean, Jacob, Manx Loaghtan, the Navajo-Churro. Horns have a curved or spiral shape with ridges or fluting. In many species only males have horns. Horns start to grow soon after birth, continue to grow throughout the life of the animal. Partial or deformed horns in livestock are called scurs. Similar growths on other parts of the body are not called horns, but spurs, claws or hoofs depending on the part of the body on which they occur; the term "horn" is popularly applied to other hard and pointed features attached to the head of animals in various other families: Giraffidae: Giraffes have one or more pairs of bony bumps on their heads, called ossicones.
These are covered with furred skin. Cervidae: Most deer have antlers, which are not true horns; when developed, antlers are dead bone without a horn or skin covering. Rhinocerotidae: The "horns" of rhinoceroses are made of keratin, the same substance as fingernails, grow continuously, but do not have a bone core. Chamaeleonidae: Many chameleons, most notably the Jackson's chameleon, possess horns on their skulls, have a keratin covering. Ceratopsidae: The "horns" of the Triceratops were extensions of its skull bones although debate exists over whether they had a keratin covering. Abelisauridae: various abelisaurid theropods, such as Carnotaurus and Majungasaurus possessed extensions of the frontal bone which were covered in some form of keratinous integument. Horned lizards: These lizards have horns on their heads which have a hard keratin covering over a bony core, like mammalian horns. Insects: Some insects have horn-like structures on the head or thorax; these are pointed outgrowths of the hard chitinous exoskeleton.
Some have enlarged jaws made of chitin. Canidae: Golden jackals are known to develop a horny growth on the skull, associated with magical powers in south-eastern Asia. Azendohsauridae: the skull of the triassic azendohsaurid archosauromorph Shringasaurus possessed two massive, forward-facing conical horns, which were covered in cornified sheaths in life. Anhimidae: The horned screamer possesses an keratinous spine, loosely connected to its skull. Many mammal species in various families have tusks, which serve the same functions as horns, but are in fact oversized teeth; these include the Moschidae, Proboscidea and Odobenidae. Polled animals or pollards are those of normally-horned species whose horns have been removed, or which have not grown. In some cases such animals have small horny growths in the skin where their horns would be – these are known as scurs. Cutaneous horns are the only examples of horns growing on people, they are most benign growths and can be removed by a razor. Cases of people growing horns have been described, sometimes with mythical status.
Researchers have not however discovered photographic evidence of the phenomenon. There are human cadaveric specimens that show outgrowings, but these are instead classified as osteomas or other excrescences; the phenomenon of humans with horns has been observed in countries lacking advanced medicine. There are living people, several in China, with cases of cutaneous horns, most common in the elderly; some people, notably The Enigma, have horn implants. The erect penis is sometimes referred to in slang use as a "horn", but it contains no keratin. However, a cutaneous horn can grow on the penis. Animals have a variety of uses for horns and antlers, including defending themselves from predators and fighting members of their own species for territory, dominance or mating priority. Horns are present only in males but in some species, females too may possess horns, it has been theorized by researchers that taller species living in the open are more visible from longer distances and more to benefit from horns to defend themselves against predators.
Female bovids that are not hidden from predators due to their large size or open savannah like habitat are more to bear horns than small or camouflaged species. In addition, horns may be used to root in the strip bark from trees. In animal courtship many use horns in displays. For example, the male blue wildebeest reams the bark and branches of trees to impress the female and lure her into his territory; some animals with true horns use them for cooling. The blood vessels in the bony core allow the horns to function as a radiator. After the death of a horned animal, the keratin may be consumed by the larvae of the Horn Moth. Horned animals are sometimes hunted so their mounted head or horns can be displayed as a hunting trophy or as decorative objects; some cultures use bovid horns for example, the shofar. These have evolved into brass instruments in which, unli