Bernard Germain de Lacépède
Bernard-Germain-Étienne de La Ville-sur-Illon, comte de Lacépède or La Cépède was a French naturalist and an active freemason. He is known for his contribution to the Histoire Naturelle. Lacépède was born at Agen in Guienne, his education was conducted by his father, the early perusal of Buffon's Natural History awakened his interest in that branch of study, which absorbed his chief attention. His leisure he devoted to music, in which, besides becoming a good performer on the piano and organ, he acquired considerable mastery of composition, two of his operas meeting with the high approval of Gluck. Meantime he wrote two treatises, Essai sur l'électricité and Physique générale et particulaire, which gained him the friendship of Buffon, who in 1785 appointed him subdemonstrator in the Jardin du Roi, proposed that he continue Buffon's Histoire naturelle; this continuation was published under the titles Histoire naturelle des quadrupèdes ovipares et des serpents. Tome premier and Histoire naturelle des serpents.
Tome second. After the French Revolution Lacépède became a member of the Legislative Assembly, but during the Reign of Terror he left Paris, his life having become endangered by his disapproval of the massacres; when the Jardin du Roi was reorganised as the Jardin des Plantes, Lacépède was appointed to the chair allocated to the study of reptiles and fishes. In 1798, he published the first volume of Histoire naturelle des poissons, the fifth volume appearing in 1803, in 1804 appeared his Histoire des cétacées. From this period until his death the part he took in politics prevented him making any further contribution of importance to science. In 1799, he became a senator, in 1801 president of the senate, in 1803 grand chancellor of the Legion of Honor, in 1804 minister of state, at the Bourbon Restoration in 1819 he was created a peer of France, he died at Épinay-sur-Seine. During the latter part of his life he wrote Histoire générale physique et civile de l'Europe, published posthumously in 18 volumes, 1826.
He was elected a member of the Institute of France in 1796, a Fellow of the Royal Society in 1806 and a foreign member of the Royal Swedish Academy of Sciences in 1812. Lacépède was initiated into freemasonry at 22 years old at Les Neuf Sœurs lodge in Paris, by Jérôme Lalande the worshipfull master himself, who wanted a naturalist for his prestigious lodge. In 178.5 millionépède created his own lodge: "Les Frères Initiés". After the Revolution, he helped Cambacérès to rebuild a French freemasonry submitted to the Emperor, joined "Saint-Napoléon" lodge where General Kellermann was worshipfull master, he finished his masonic life as dignitary of the Suprême Conseil de France. Lacepede Bay in South Australia, the Lacepede Islands off the northern coast of Western Australia, are named after him, as is the Rue Lacepede near the Jardin des Plantes. A species of gecko endemic to Mauritius, Phelsuma cepediana, is named in his honour. Lacépède was an early evolutionary thinker, he argued for the transmutation of species.
He believed that species change over time and may go extinct from geological cataclysms or become "metamorphosed" into new species. In his book Histoire naturelle des poissons, he wrote: "The species can undergo such a large number of modifications in its forms and qualities, that without losing its vital capacity, it may be, by its latest conformation and properties, farther removed from its original state than from a different species: it is in that case metamorphosed into a new species." Les ages de la nature et histoire de l'espèce humaine. Paris 1830 p.m. Histoire naturelle de l'homme. Pitois-Le Vrault, Paris 1827 p.m. Histoire générale, physique et civile de l'Europe. Cellot, Delaunay-Vallée & de Mat, Paris, Brüssel 1826 p.m. Histoire naturelle des quadrupèdes ovipares, poissons et cétacées. Eymery, Paris 1825. Histoire naturelle des cétacées. Plassan, Paris 1804. Notice historique sur la vie et les ouvrages de Dolomieu. Bossange, Paris 1802. La menagerie du Museum national d'histoire naturelle.
Miger, Paris 1801–04. Discours d'ouverture et de clôture. Plassan, Paris 1801. Discours d'ouverture et de clôture. Plassan, Paris 1799. Histoire naturelle des poissons. Plassan, Paris 1798–1803. Discours d'ouverture et de clôture du cours d'histoire naturelle des animaux vertébrés et a sang rouge. Plassan, Paris 1798. Discours d'ouverture du Cours d'histoire naturelle. Paris 1797. Histoire naturelle des serpents. Tome second. De Thou, Paris 1789. Histoire naturelle des quadrupèdes ovipares et des serpens. Tome premier. De Thou, Paris 1788. Vie de Buffon. Maradan, Amsterdam 1788. La poétique de la musique. Paris 1785. Physique générale. Paris 1782–84. Essai sur l'électricité naturelle et artificielle. Paris 1781. Schmitt, Stéphane. "Lacepède’s syncretic contribution to the debates on natural history in France around 1800". Journal of the History of Biology 43: 429-457. Cuvier, Georges. Éloges historiques de MM. de Saussure, Hauy, de Lacépède et Cavendish. Münster: Theissing.. Saloman, Ora Frishberg. Aspects of "Gluckian" operatic practice in France.
Ann Arbor. Roule, Louis. Lacépède, professeur au Muséum, premier grand chancellier de la Légion d'honneur, et la sociologie humanitaire selon la nature. Paris: Flammarion.. Internet Archive Works by Lacepede Lacépède Histoire naturelle 2 vol. – Linda Hall Library
Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of invertebrates include arthropods, mollusks and cnidarians; the majority of animal species are invertebrates. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata; some of the so-called invertebrates, such as the Tunicata and Cephalochordata are more related to the vertebrates than to other invertebrates. This makes the invertebrates paraphyletic, so the term has little meaning in taxonomy; the word "invertebrate" comes from the Latin word vertebra, which means a joint in general, sometimes a joint from the spinal column of a vertebrate. The jointed aspect of vertebra is derived from the concept of turning, expressed in the root verto or vorto, to turn; the prefix in- means "not" or "without". The term invertebrates is not always precise among non-biologists since it does not describe a taxon in the same way that Arthropoda, Vertebrata or Manidae do.
Each of these terms describes a valid taxon, subphylum or family. "Invertebrata" is a term of convenience, not a taxon. The Vertebrata as a subphylum comprises such a small proportion of the Metazoa that to speak of the kingdom Animalia in terms of "Vertebrata" and "Invertebrata" has limited practicality. In the more formal taxonomy of Animalia other attributes that logically should precede the presence or absence of the vertebral column in constructing a cladogram, for example, the presence of a notochord; that would at least circumscribe the Chordata. However the notochord would be a less fundamental criterion than aspects of embryological development and symmetry or bauplan. Despite this, the concept of invertebrates as a taxon of animals has persisted for over a century among the laity, within the zoological community and in its literature it remains in use as a term of convenience for animals that are not members of the Vertebrata; the following text reflects earlier scientific understanding of the term and of those animals which have constituted it.
According to this understanding, invertebrates do not possess a skeleton of bone, either internal or external. They include hugely varied body plans. Many have like jellyfish or worms. Others have outer shells like those of insects and crustaceans; the most familiar invertebrates include the Protozoa, Coelenterata, Nematoda, Echinodermata and Arthropoda. Arthropoda include insects and arachnids. By far the largest number of described invertebrate species are insects; the following table lists the number of described extant species for major invertebrate groups as estimated in the IUCN Red List of Threatened Species, 2014.3. The IUCN estimates that 66,178 extant vertebrate species have been described, which means that over 95% of the described animal species in the world are invertebrates; the trait, common to all invertebrates is the absence of a vertebral column: this creates a distinction between invertebrates and vertebrates. The distinction is one of convenience only. Being animals, invertebrates are heterotrophs, require sustenance in the form of the consumption of other organisms.
With a few exceptions, such as the Porifera, invertebrates have bodies composed of differentiated tissues. There is typically a digestive chamber with one or two openings to the exterior; the body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical. A minority, exhibit no symmetry. One example of asymmetric invertebrates includes all gastropod species; this is seen in snails and sea snails, which have helical shells. Slugs appear externally symmetrical. Other gastropods develop external asymmetry, such as Glaucus atlanticus that develops asymmetrical cerata as they mature; the origin of gastropod asymmetry is a subject of scientific debate. Other examples of asymmetry are found in hermit crabs, they have one claw much larger than the other. If a male fiddler loses its large claw, it will grow another on the opposite side after moulting. Sessile animals such as sponges are asymmetrical alongside coral colonies. Neurons differ in invertebrates from mammalian cells.
Invertebrates cells fire in response to similar stimuli as mammals, such as tissue trauma, high temperature, or changes in pH. The first invertebrate in which a neuron cell was identified was the medicinal leech, Hirudo medicinalis. Learning and memory using nociceptors in the sea hare, Aplysia has been described. Mollusk neurons are able to detect tissue trauma. Neurons have been identified in a wide range of invertebrate species, including annelids, molluscs and arthropods. One type of invertebrate respi
Lorenz Oken was a German naturalist, botanist and ornithologist. Oken was born Lorenz Okenfuss in Bohlsbach, Ortenau and studied natural history and medicine at the universities of Freiburg and Würzburg, he went on to the University of Göttingen, where he became a Privatdozent, shortened his name to Oken. As Lorenz Oken, he published a small work entitled Grundriss der Naturphilosophie, der Theorie der Sinne, mit der darauf gegründeten Classification der Thiere; this was the first of a series of works which established him as a leader of the movement of "Naturphilosophie" in Germany. In it he extended to physical science the philosophical principles which Immanuel Kant had applied to epistemology and morality. Oken had been preceded in this by Gottlieb Fichte, acknowledging that Kant had discovered the materials for a universal science, declared that all, needed was a systematic coordination of these materials. Fichte undertook this task in his "Doctrine of Science", whose aim was to construct all knowledge by a priori means.
This attempt, sketched out by Fichte, was further elaborated by the philosopher Friedrich Schelling. Oken built on Schelling's work. Oken produced the seven-volume series Allgemeine Naturgeschichte für alle Stände, with engravings by Johann Susemihl, published in Stuttgart by Hoffman between 1839 and 1841. In the Grundriss der Naturphilosophie of 1802 Oken sketched the outlines of the scheme he afterwards devoted himself to perfecting; the position advanced in that work, to which he continued to adhere, is that "the animal classes are nothing else than a representation of the sense-organs, that they must be arranged in accordance with them." Oken contended that there are only five animal classes: Dermatozoa, or invertebrates Glossozoa, or fish, those animals in which a true tongue makes, for the first time, its appearance Rhinozoa, or reptiles, in which the nose opens for the first time into the mouth and inhales air Otozoa, or birds, in which the ear for the first time opens externally Ophthalmozoa, or mammals, in which all the organs of sense are present and complete, the eyes being movable and covered with lids.
In 1805 Oken made a further advance in the application of the a priori principle in a book on generation, in which he maintained that "all organic beings originate from and consist of vesicles or cells. These vesicles, when singly detached and regarded in their original process of production, are the infusorial mass or protoplasma whence all larger organisms fashion themselves or are evolved, their production is therefore nothing else than a regular agglomeration of Infusoria—not, of course, of species elaborated or perfect, but of mucous vesicles or points in general, which first form themselves by their union or combination into particular species."A year after the production of this treatise, Oken developed his system one stage further, in a volume published in 1806, written with the assistance of Dietrich von Kieser, entitled Beiträge zur vergleichenden Zoologie, und Physiologie, he demonstrated that the intestines originate from the umbilical vesicle, that this corresponds to the vitellus or yolk-bag.
Caspar Wolff had claimed to demonstrate this fact in the chick, but he did not see its application as evidence of a general law. Oken showed the importance of the discovery as an illustration of his system. In the same work Oken described and recalled attention to the corpora Wolffiana, or "primordial kidneys." The reputation of the young Privatdozent of Göttingen had reached the ear of Johann von Goethe, in 1807 Oken was invited to fill the office of Extraordinary Professor of the Medical Sciences at the University of Jena. He selected for the subject of his inaugural discourse his ideas on the "Signification of the Bones of the Skull," based on a discovery of the previous year; this lecture was delivered in the presence of Goethe, as privy councillor and rector of the university, was published in the same year, with the title, Ueber die Bedeutung der Schädelknochen. With regard to the origin of the idea, Oken narrates in his Isis that, walking one autumn day in 1806 in the Harz forest, he stumbled on the blanched skull of a deer, picked up the dislocated bones, contemplated them for a while, when it occurred to him, "It is a vertebral column!"
At a meeting of the German naturalists held at Jena some years afterwards, Professor Kieser gave an account of Oken's discovery in the presence of the grand duke, printed in the Tageblatt, or "proceedings,” of that meeting. The professor stated that Oken told him of his discovery when journeying in 1806 to the island of Wangerooge. On their return to Göttingen, Oken explained his ideas by reference to the skull of a turtle in Kieser's collection, which he disarticulated for that purpose. Kieser displayed the skull, its bones marked in Oken's handwriting. Oken's lectures at Jena were wide-ranging, were regarded at the time; the subjects included natural philosophy, general natural history, comparative anatomy, the physiology of man, of animals and of plants. The spirit with which he grappled with the vast scope of science is characteristically illustrated in his essay Ueber das Universum als Fortsetzung des Sinnensystems. In this work he lays it down that "organism is none other than a combination of all the universe's activities within a single individual body."
This doctrine led him to the conviction t
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
Crustaceans form a large, diverse arthropod taxon which includes such familiar animals as crabs, crayfish, krill and barnacles. The crustacean group is treated as a subphylum, because of recent molecular studies it is now well accepted that the crustacean group is paraphyletic, comprises all animals in the Pancrustacea clade other than hexapods; some crustaceans are more related to insects and other hexapods than they are to certain other crustaceans. The 67,000 described species range in size from Stygotantulus stocki at 0.1 mm, to the Japanese spider crab with a leg span of up to 3.8 m and a mass of 20 kg. Like other arthropods, crustaceans have an exoskeleton, they are distinguished from other groups of arthropods, such as insects and chelicerates, by the possession of biramous limbs, by their larval forms, such as the nauplius stage of branchiopods and copepods. Most crustaceans are free-living aquatic animals, but some are terrestrial, some are parasitic and some are sessile; the group has an extensive fossil record, reaching back to the Cambrian, includes living fossils such as Triops cancriformis, which has existed unchanged since the Triassic period.
More than 10 million tons of crustaceans are produced by fishery or farming for human consumption, the majority of it being shrimp and prawns. Krill and copepods are not as fished, but may be the animals with the greatest biomass on the planet, form a vital part of the food chain; the scientific study of crustaceans is known as carcinology, a scientist who works in carcinology is a carcinologist. The body of a crustacean is composed of segments, which are grouped into three regions: the cephalon or head, the pereon or thorax, the pleon or abdomen; the head and thorax may be fused together to form a cephalothorax, which may be covered by a single large carapace. The crustacean body is protected by the hard exoskeleton, which must be moulted for the animal to grow; the shell around each somite can be divided into a dorsal tergum, ventral sternum and a lateral pleuron. Various parts of the exoskeleton may be fused together; each somite, or body segment can bear a pair of appendages: on the segments of the head, these include two pairs of antennae, the mandibles and maxillae.
The abdomen bears pleopods, ends in a telson, which bears the anus, is flanked by uropods to form a tail fan. The number and variety of appendages in different crustaceans may be responsible for the group's success. Crustacean appendages are biramous, meaning they are divided into two parts, it is unclear whether the biramous condition is a derived state which evolved in crustaceans, or whether the second branch of the limb has been lost in all other groups. Trilobites, for instance possessed biramous appendages; the main body cavity is an open circulatory system, where blood is pumped into the haemocoel by a heart located near the dorsum. Malacostraca have haemocyanin as the oxygen-carrying pigment, while copepods, ostracods and branchiopods have haemoglobins; the alimentary canal consists of a straight tube that has a gizzard-like "gastric mill" for grinding food and a pair of digestive glands that absorb food. Structures that function as kidneys are located near the antennae. A brain exists in the form of ganglia close to the antennae, a collection of major ganglia is found below the gut.
In many decapods, the first pair of pleopods are specialised in the male for sperm transfer. Many terrestrial crustaceans return to the sea to release the eggs. Others, such as woodlice, lay their eggs on land, albeit in damp conditions. In most decapods, the females retain the eggs; the majority of crustaceans are aquatic, living in either marine or freshwater environments, but a few groups have adapted to life on land, such as terrestrial crabs, terrestrial hermit crabs, woodlice. Marine crustaceans are as ubiquitous in the oceans; the majority of crustaceans are motile, moving about independently, although a few taxonomic units are parasitic and live attached to their hosts, adult barnacles live a sessile life – they are attached headfirst to the substrate and cannot move independently. Some branchiurans are able to withstand rapid changes of salinity and will switch hosts from marine to non-marine species. Krill are the bottom layer and the most important part of the food chain in Antarctic animal communities.
Some crustaceans are significant invasive species, such as the Chinese mitten crab, Eriocheir sinensis, the Asian shore crab, Hemigrapsus sanguineus. The majority of crustaceans have separate sexes, reproduce sexually. A small number are hermaphrodites, including barnacles and Cephalocarida; some may change sex during the course of their life. Parthenogenesis is widespread among crustaceans, where viable eggs are produced by a female without needing fertilisation by a male; this occurs in many branchiopods, some os
The Atlantic Ocean is the second largest of the world's oceans, with an area of about 106,460,000 square kilometers. It covers 20 percent of the Earth's surface and about 29 percent of its water surface area, it separates the "Old World" from the "New World". The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, the Americas to the west; as one component of the interconnected global ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, the Southern Ocean in the south. The Equatorial Counter Current subdivides it into the North Atlantic Ocean and the South Atlantic Ocean at about 8°N. Scientific explorations of the Atlantic include the Challenger expedition, the German Meteor expedition, Columbia University's Lamont-Doherty Earth Observatory and the United States Navy Hydrographic Office; the oldest known mentions of an "Atlantic" sea come from Stesichorus around mid-sixth century BC: Atlantikoi pelágei and in The Histories of Herodotus around 450 BC: Atlantis thalassa where the name refers to "the sea beyond the pillars of Heracles", said to be part of the sea that surrounds all land.
Thus, on one hand, the name refers to Atlas, the Titan in Greek mythology, who supported the heavens and who appeared as a frontispiece in Medieval maps and lent his name to modern atlases. On the other hand, to early Greek sailors and in Ancient Greek mythological literature such as the Iliad and the Odyssey, this all-encompassing ocean was instead known as Oceanus, the gigantic river that encircled the world. In contrast, the term "Atlantic" referred to the Atlas Mountains in Morocco and the sea off the Strait of Gibraltar and the North African coast; the Greek word thalassa has been reused by scientists for the huge Panthalassa ocean that surrounded the supercontinent Pangaea hundreds of millions of years ago. The term "Aethiopian Ocean", derived from Ancient Ethiopia, was applied to the Southern Atlantic as late as the mid-19th century. During the Age of Discovery, the Atlantic was known to English cartographers as the Great Western Ocean; the term The Pond is used by British and American speakers in context to the Atlantic Ocean, as a form of meiosis, or sarcastic understatement.
The term dates to as early as 1640, first appearing in print in pamphlet released during the reign of Charles I, reproduced in 1869 in Nehemiah Wallington's Historical Notices of Events Occurring Chiefly in The Reign of Charles I, where "great Pond" is used in reference to the Atlantic Ocean by Francis Windebank, Charles I's Secretary of State. The International Hydrographic Organization defined the limits of the oceans and seas in 1953, but some of these definitions have been revised since and some are not used by various authorities and countries, see for example the CIA World Factbook. Correspondingly, the extent and number of oceans and seas varies; the Atlantic Ocean is bounded on the west by South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea and Barents Sea. To the east, the boundaries of the ocean proper are Europe: the Strait of Africa. In the southeast, the Atlantic merges into the Indian Ocean; the 20° East meridian, running south from Cape Agulhas to Antarctica defines its border.
In the 1953 definition it extends south to Antarctica, while in maps it is bounded at the 60° parallel by the Southern Ocean. The Atlantic has irregular coasts indented by numerous bays and seas; these include the Baltic Sea, Black Sea, Caribbean Sea, Davis Strait, Denmark Strait, part of the Drake Passage, Gulf of Mexico, Labrador Sea, Mediterranean Sea, North Sea, Norwegian Sea all of the Scotia Sea, other tributary water bodies. Including these marginal seas the coast line of the Atlantic measures 111,866 km compared to 135,663 km for the Pacific. Including its marginal seas, the Atlantic covers an area of 106,460,000 km2 or 23.5% of the global ocean and has a volume of 310,410,900 km3 or 23.3% of the total volume of the earth's oceans. Excluding its marginal seas, the Atlantic covers 81,760,000 km2 and has a volume of 305,811,900 km3; the North Atlantic covers 41,490,000 km2 and the South Atlantic 40,270,000 km2. The average depth is 3,646 m and the maximum depth, the Milwaukee Deep in the Puerto Rico Trench, is 8,486 m.
The bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge. It runs from 87°N or 300 km south of the North Pole to the subantarctic Bouvet Island at 42°S; the MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above 2,000 m along most of its length, but is interrupted by larger transform faults at two places: the Romanche Trench near the Equator and the Gibbs Fracture Zone at 53°N; the MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the othe
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates such as fishes and the ichthyosaur. Most species have only one dorsal fin. Wildlife biologists use the distinctive nicks and wear patterns which develop on the dorsal fins of large cetaceans to identify individuals in the field; the bony or cartilaginous bones that support the base of the dorsal fin in fish are called pterygiophores. The main purpose of the dorsal fin is to stabilize the animal against rolling and to assist in sudden turns; some species have further adapted their dorsal fins to other uses. The sunfish uses the dorsal fin for propulsion. In anglerfish, the anterior of the dorsal fin is modified into a biological equivalent to a fishing pole and a lure known as illicium or esca. Many catfish can lock the leading ray of the dorsal fin in an extended position to discourage predation or to wedge themselves into a crevice; some animals have developed dorsal fins with protective functions, such as spines or venom.
For example, both the spiny dogfish and the Port Jackson shark have spines in their dorsal fins which are capable of secreting venom. Billfish have prominent dorsal fins. Like tuna and other scombroids, billfish streamline themselves by retracting their dorsal fins into a groove in their body when they swim; the shape, size and colour of the dorsal fin varies with the type of billfish, can be a simple way to identify a billfish species. For example, the white marlin has a dorsal fin with a curved front edge and is covered with black spots; the huge dorsal fin, or sail, of the sailfish is kept retracted most of the time. Sailfish raise them if they want to herd a school of small fish, after periods of high activity to cool down. A dorsal fin is classified as a medial, unpaired fin, located on the midline of the backs of some aquatic vertebrates. In development of the embryo in teleost fish, the dorsal fin arises from sections of the skin that form a caudal fin fold; the larval development and formation of the skeleton that support the median fins in adults result in pterygiophores.
The skeletal elements of the pterygiophore includes radials. The basals are located at the base of the dorsal fin, are closest to the body; the radials extend outward from the body to support the rest of the fin. These elements serve as attachment sites for epaxial muscles; the muscles contract and pull against the basals of the pterygiophores along one side of the body, which helps the fish move through water by providing greater stability. In these types of fish, the fins are made of 2 main components; the first component is the dermal fin rays known as lepidotrichia, the endoskeletal base with associated muscles for movement is the second. Fish fin Submarine sail Vertical stabilizer