The Permian is a geologic period and system which spans 46.7 million years from the end of the Carboniferous Period 298.9 million years ago, to the beginning of the Triassic Period 252.2 Mya. It is the last period of the Paleozoic Era, the following Triassic Period belongs to the Mesozoic Era, the concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm. The Permian witnessed the diversification of the early amniotes into the groups of the mammals, lepidosaurs. The world at the time was dominated by two known as Pangaea and Siberia, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors. The Permian ended with the Permian–Triassic extinction event, the largest mass extinction in Earths history, in which nearly 90% of marine species and it would take well into the Triassic for life to recover from this catastrophe.
Recovery from the Permian-Triassic extinction event was protracted, on land, the term Permian was introduced into geology in 1841 by Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil, the region now lies in the Perm Krai of Russia. This could have in part caused the extinctions of marine species at the end of the period by severely reducing shallow coastal areas preferred by many marine organisms. During the Permian, all the Earths major landmasses were collected into a supercontinent known as Pangaea. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, a new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmass interiors experience climates with extreme variations of heat and cold, deserts seem to have been widespread on Pangaea. Such dry conditions favored gymnosperms, plants with seeds enclosed in a cover, over plants such as ferns that disperse spores in a wetter environment.
The first modern trees appeared in the Permian, the climate in the Permian was quite varied. At the start of the Permian, the Earth was still in an Ice Age, glaciers receded around the mid-Permian period as the climate gradually warmed, drying the continents interiors. In the late Permian period, the drying continued although the temperature cycled between warm and cool cycles, Permian marine deposits are rich in fossil mollusks and brachiopods. By the close of the Permian, trilobites and a host of other groups became extinct. Terrestrial life in the Permian included diverse plants, arthropods, the period saw a massive desert covering the interior of Pangaea
Clam is a common name for several kinds of bivalve molluscs. The word is applied only to those that live as infauna. In particular, edible infaunal bivalves are often called clams, clams have two shells of equal size connected by two adductor muscles and have a powerful burrowing foot. Clams in the culinary sense do not live attached to a substrate, in culinary usage, clams are commonly eaten marine bivalves, as in clam digging and the resulting soup, clam chowder. Many edible clams such as palourde clams are oval or triangular, razor clams have an elongated parallel-sided shell, some clams have life cycles of only one year, while at least one may be over 500 years old. All clams have two shells or valves joined near a hinge with a flexible ligament, and all are filter feeders. A clams shell consists of two valves, which are connected by a joint and a ligament that can be external or internal. The ligament provides tension to bring the valves apart, while one or two muscles can contract to close the valves.
Clams have kidneys, a heart, a mouth, a stomach, a nervous system, in culinary use, within the eastern coast of the United States, the term clam most often refers to the hard clam Mercenaria mercenaria. It may refer to a few other common species, such as the soft-shell clam, Mya arenaria. Another species commercially exploited on the Atlantic Coast of the United States is the surf clam Spisula solidissima, scallops are used for food. Clams can be raw, boiled, baked or fried. They can be made into clam chowder or they can be cooked using hot rocks, in Japan, clams are often an ingredient of mixed seafood dishes. They can be made into hot pot, miso soup or Tsukudani, the more commonly used varieties of clams in Japanese cooking are the Shijimi, the Asari and the Hamaguri. In Italy, clams are often an ingredient of mixed seafood dishes or are eaten together with pasta, the more commonly used varieties of clams in Italian cooking are the Vongola, the Cozza and the Tellina. Clams are eaten more in the regions of India, especially in the Konkan, Bengal.
In Kerala clams are used to make curries and fried with coconut, in Malabar region it is known as elambakka and in middle kerala it is known as kakka. Clams curry made with coconut is a delicious dish from malabar especially in Telicherry region
Rajiformes is one of the four orders in the superorder Batoidea, flattened cartilaginous fishes related to sharks. Rajiforms are distinguished by the presence of greatly enlarged pectoral fins, the undulatory pectoral fin motion diagnostic to this taxon is known as rajiform locomotion. The eyes and spiracles are located on the surface of the head. Most species give birth to young, although some lay eggs with a horny capsule. Rajoids typically have a flattened body. The snout is slender and pointed and the mouth, often covered with a fleshy nasal flap, is on the underside of the head. The eyes and well-developed spiracles are located on the top of the head, in most species, the spiracles are large and are the main means of drawing water in for respiration. There is no nictitating membrane and the cornea is continuous with the surrounding the eyes. The gill slits are on the surface just behind the head. Most species have enlarged, thorn-like dermal denticles on their skin, the pectoral fins are large, but not clearly demarcated from the body, and together with the body are known as the disc.
They start from the side of the head in front of the gill openings, there are up to two dorsal fins but no anal fin. A slender tail is clearly demarcated from the disc, the caudal fin varies in size between species and the rays have a whip-like tail with no caudal fin. Species of the order Rajiformes are found throughout the oceans, from Arctic to Antarctic waters. A few are found in rivers and some in estuaries, but most are marine and they are small fish living on the continental slopes of tropical and subtropical waters, and are native to Natal, South Africa, tropical West Africa, and Taiwan. Smooth skates have a filament extending from a rounded protuberance on the snout, both the dorsal and ventral surfaces are smooth and have no dermal denticles. The tail is slender and a shorter than the body. No dorsal fins are present and the fin is small. The skate family Rajidae contains 14 genera and around 200 species and they are found worldwide, but are relatively uncommon near coral reefs and in shallow tropical seas
Anatomical terms of location
Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. All vertebrates have the basic body plan – they are strictly bilaterally symmetrical in early embryonic stages. That is, they have left and right halves if divided down the centre. For these reasons, the directional terms can be considered to be those used in vertebrates. By extension, the terms are used for many other organisms as well. While these terms are standardized within specific fields of biology, there are unavoidable, sometimes dramatic, for example, differences in terminology remain a problem that, to some extent, still separates the terminology of human anatomy from that used in the study of various other zoological categories. The vertebrates and Craniata share a heritage and common structure. To avoid ambiguities this terminology is based on the anatomy of each animal in a standard way, for humans, one type of vertebrate, anatomical terms may differ from other forms of vertebrates.
Thus what is on top of a human is the head, whereas the top of a dog may be its back, for example, many species are not even bilaterally symmetrical. In these species, terminology depends on their type of symmetry, all descriptions are with respect to the organism in its standard anatomical position, even when the organism in question has appendages in another position. This helps avoid confusion in terminology when referring to the organism in different postures. In humans, this refers to the body in a position with arms at the side. While the universal vertebrate terminology used in medicine would work in human medicine. Many anatomical terms can be combined, either to indicate a position in two axes simultaneously or to indicate the direction of a movement relative to the body, for example, anterolateral indicates a position that is both anterior and lateral to the body axis. There is no limit to the contexts in which terms may be modified to qualify each other in such combinations. Generally the modifier term is truncated and an o or an i is added in prefixing it to the qualified term, where desirable three or more terms may be agglutinated or concatenated, as in anteriodorsolateral.
Such terms sometimes used to be hyphenated, but the tendency is to omit the hyphen. There is however little basis for any rule to interfere with choice of convenience in such usage
The class is divided into two subclasses and Holocephali. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates, the notochord, which is present in the young, is gradually replaced by cartilage. Chondrichthyans lack ribs, so if they leave water, the larger species own body weight would crush their internal organs long before they would suffocate, as they do not have bone marrow, red blood cells are produced in the spleen and the epigonal organ. They are produced in the Leydigs organ, which is found in certain cartilaginous fishes. The subclass Holocephali, which is a specialized group, lacks both the Leydigs and epigonal organs. In most species, all dermal denticles are oriented in one direction, making the skin feel very smooth if rubbed in one direction, the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In forms, each pair of fins became ventrally connected in the middle when scapulocoracoid, in rays, the pectoral fins have connected to the head and are very flexible.
One of the characteristics present in most sharks is the heterocercal tail. Chondrichthyans have toothlike scales called dermal denticles or placoid scales, denticles provide two functions, protection and in most cases, streamlining. Mucous glands exist in species as well. This is most likely an evolved characteristic, which means there is not necessarily a connection between the teeth and the original dermal scales. The old placoderms did not have teeth at all, but had sharp bony plates in their mouth, thus, it is unknown whether the dermal or oral teeth evolved first. Nor is it sure how many times it has happened if it out to be the case. However, there is no evidence of this at the moment, all chondrichthyans breathe through five to seven pairs of gills, depending on the species. However, this is only a rule and many species differ. A spiracle is a hole found behind each eye. These can be tiny and circular, such as found on the shark, to extended and slit-like. Many larger, pelagic species, such as the mackerel sharks, like all other jawed vertebrates, members of Chondrichthyes have an adaptive immune system
The skin of most fishes are covered with scales. The morphology of a scale can be used to identify the species of fish it came from, cartilaginous fishes are covered with placoid scales. Most bony fishes are covered with the scales of salmon and carp, or the ctenoid scales of perch, or the ganoid scales of sturgeons. Some species are covered instead by scutes, and others have no outer covering on the skin, fish scales are part of the fishs integumentary system, and are produced from the mesoderm layer of the dermis, which distinguishes them from reptile scales. The same genes involved in tooth and hair development in mammals are involved in scale development, the placoid scales of cartilaginous fishes are called dermal denticles and are structurally homologous with vertebrate teeth. It has been suggested that the scales of bony fishes are similar in structure to teeth, most fish are covered in a protective layer of mucus. Placoid scales are found in the fishes, rays. They are called dermal denticles, the outermost layer is composed of vitrodentine, a largely inorganic enamel-like substance.
Placoid scales cannot grow in size, but rather more scales are added as the fish increases in size, similar scales can be found under the head of the denticle herring. The amount of coverage is much less in rays and chimaeras. The skin of sharks is entirely covered by placoid scales, the rough, sandpaper-like texture of shark and ray skin, coupled with its toughness, has led it to be valued as a source of rawhide leather, called shagreen. One of the historical applications of shark shagreen was in making hand-grips for swords. Unlike bony fish, sharks have a complicated dermal corset made of collagenous fibers arranged as a helical network surrounding their body. The corset works as a skeleton, providing attachment for their swimming muscles. Their dermal teeth give them hydrodynamic advantages, as the scales reduce the turbulence of swimming, leptoid scales are found on higher-order bony fish, the teleosts. As the fish grow, scales are added in concentric layers, the scales are arranged so as to overlap in a head-to-tail configuration, like roof tiles, allowing a smoother flow of water over the body and thereby reducing drag.
Leptoid scales come in two forms and ctenoid, cycloid scales have a smooth texture and are uniform, with a smooth outer edge or margin. They are most common on fish with fin rays, such as salmon
The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya and its subdivisions, and its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, as a result, our understanding of the Cambrian biology surpasses that of some periods. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia, the seas were relatively warm, and polar ice was absent for much of the period. The United States Federal Geographic Data Committee uses a barred capital C ⟨Є⟩ character similar to the capital letter Ukrainian Ye ⟨Є⟩ to represent the Cambrian Period, the proper Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR.
Despite the long recognition of its distinction from younger Ordovician Period rocks and older Supereon Precambrian rocks, the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. Pedum in Namibia and Newfoundland, and possibly, in the western USA, the stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain. The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period, the Cambrian is divided into four epochs and ten ages. Currently only two series and five stages are named and have a GSSP, because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian, Middle Cambrian and Furongian, rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.
Trilobite zones allow biostratigraphic correlation in the Cambrian, each of the local epochs is divided into several stages. The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago, the lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier and this formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour, though the used to obtain this number are now considered to be unsuitable. A more precise date using modern radiometric dating yield a date of 541 ±0.3 million years ago, most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian, the sea levels fluctuated somewhat, suggesting there were ice ages, associated with pulses of expansion and contraction of a south polar ice cap.
In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into a epicontinental sea, the Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents
The Precambrian is the earliest period of Earths history, set before the current Phanerozoic Eon. The Precambrian is a supereon that is subdivided into three eons of the time scale. It spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 541 million years ago, the Precambrian accounts for 89% of geologic time. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earths history, the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from that time are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion. A stable crust was apparently in place by 4,412 Ma, the term Precambrian is recognized by the International Commission on Stratigraphy as a general term including the Archean and Proterozoic eons. It is still used by geologists and paleontologists for general discussions not requiring the more specific eon names and it was briefly called the Cryptozoic eon.
A specific date for the origin of life has not been determined, carbon found in 3.8 billion year old rocks from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have found in Western Australia. Probable fossils 100 million years older have been found in the same area, there is a fairly solid record of bacterial life throughout the remainder of the Precambrian. The oldest fossil evidence from that era of such complex life comes from the Lantian formation of the Ediacarian period, a very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota, hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic era. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale. The explosion in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life, while land seems to have been devoid of plants and animals and other microbes formed prokaryotic mats that covered terrestrial areas.
Evidence of the details of plate motions and other activity in the Precambrian has been poorly preserved. It is generally believed that small proto-continents existed prior to 4280 Ma, the supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, one of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a Snowball Earth. The atmosphere of the early Earth is not well understood, most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and was lacking in free oxygen
The devil fish or giant devil ray is an endangered species of eagle ray in the family Myliobatidae. It is currently listed as endangered, mostly due to mortality in unrelated fisheries. The devil fish is larger than its relative the lesser devil ray. It grows to a recorded length of 5.2 metres. Devil fish inhabit offshore areas to the zone, their range as deep as several thousand meters. They are typically observed in small clusters, and may form larger groups. Devil rays feed on crustaceans and small schooling fish, which are trapped using the modified gill covers responsible for its devil-like silhouette. The species is ovoviviparous, the hatch from their eggs inside the mothers body. Only a single young which is called a pup is born at a time. The devil fish has a range and a low rate of reproduction. As a result it is sensitive to environmental changes, the main threats to this species come from pollution in the Mediterranean and bycatch capture in various fishing equipment including trawls, tuna traps, and dragnets meant for swordfish.
The 2004 IUCN Red List listed the fish as a vulnerable species. It was reclassified as endangered in 2006 due to low population resilience coupled with continued high bycatch mortality
The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, comprising the order Torpediniformes. They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, depending on species, used to stun prey, there are 69 species in four families. Perhaps the best known members are those of the genus Torpedo, the name comes from the Latin torpere, to be stiffened or paralyzed, referring to the effect on someone who handles or steps on a living electric ray. Electric rays have a rounded pectoral disc with two moderately large dorsal fins, and a stout muscular tail with a well-developed caudal fin. The body is thick and flabby, with loose skin with no dermal denticles or thorns. A pair of kidney-shaped electric organs are at the base of the pectoral fins, the snout is broad, large in the Narcinidae, but reduced in all other families. The mouth and five pairs of gill slits are underneath the disc, electric rays are found from shallow coastal waters down to at least 1,000 m deep.
They are sluggish and slow-moving, propelling themselves with their tails and they feed on invertebrates and small fish. They lie in wait for prey below the sand or other substrate, using their electricity to stun, the electrogenic properties of electric rays have been known since antiquity. The ancient Greeks used electric rays to numb the pain of childbirth, in his dialogue Meno, Plato has the character Meno accuse Socrates of stunning people with his puzzling questions, in a manner similar to the way the torpedo fish stuns with electricity. Scribonius Largus, a Roman physician, recorded the use of fish for treatment of headaches. The electric ray may be the most electrosensitive of all animals and their eyes are on the top of their heads, resulting in poor vision that must be compensated for with the use of other senses, including detecting electricity. The organs are governed by four central nerves from each side of the lobe, or specialized brain lobe. The 60 or so species of rays are grouped into 12 genera.
The Narkinae are sometimes elevated to a family, the Narkidae, the torpedinids feed on large prey, which are stunned using their electric organs and swallowed whole, while the narcinids specialize on small prey on or in the bottom substrate. Both groups use electricity for defense, but it is whether the narcinids use electricity in feeding
Animals are multicellular, eukaryotic organisms of the kingdom Animalia. The animal kingdom emerged as a clade within Apoikozoa as the group to the choanoflagellates. Animals are motile, meaning they can move spontaneously and independently at some point in their lives and their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis in their lives. All animals are heterotrophs, they must ingest other organisms or their products for sustenance, most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates, vertebrates have a backbone or spine, and amount to less than five percent of all described animal species. They include fish, reptiles and mammals, the remaining animals are the invertebrates, which lack a backbone. These include molluscs, annelids, flatworms, ctenophores, the study of animals is called zoology.
The word animal comes from the Latin animalis, meaning having breath, the biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish and humans. Aristotle divided the world between animals and plants, and this was followed by Carl Linnaeus, in the first hierarchical classification. In Linnaeuss original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Pisces, Amphibia and Mammalia. Since the last four have all been subsumed into a single phylum, in 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms and Protozoa. The protozoa were moved to the kingdom Protista, leaving only the metazoa, thus Metazoa is now considered a synonym of Animalia. Animals have several characteristics that set apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and they are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae.
They are distinguished from plants and fungi by lacking cell walls. All animals are motile, if only at life stages. In most animals, embryos pass through a stage, which is a characteristic exclusive to animals. With a few exceptions, most notably the sponges and Placozoa and these include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals
Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish. Members of this subclass are characterised by having five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, the teeth are in several series, the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades, the pelvic fins in males are modified to create claspers for the transfer of sperm. There is no bladder, instead these fish maintain buoyancy with large livers rich in oil. The earliest elasmobranch fossils came from the Devonian and many surviving orders date back to the Cretaceous, many species became extinct during the Permian and there was a burst of adaptive radiation during the Jurassic. Extant species are classified under Selachii, the sharks, and Batoidea. Elasmobranchii is one of the two subclasses of cartilaginous fish in the class Chondrichthyes, the other being Holocephali, members of the elasmobranchii subclass have no swim bladders, five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales.
The teeth are in series, the upper jaw is not fused to the cranium. Extant elasmobranchs exhibit several archetypal jaw suspensions, orbitostyly, hyostyly, in amphistyly, the palatoquadrate has a postorbital articulation with the chondrocranium from which ligaments primarily suspend it anteriorly. The hyoid articulates with the mandibular arch posteriorly, but it appears to provide support to the upper and lower jaws. In orbitostyly, the orbital process hinges with the orbital wall, in contrast, hyostyly involves an ethmoid articulation between the upper jaw and the cranium, while the hyoid most likely provides vastly more jaw support compared to the anterior ligaments. Finally, in euhyostyly, known as true hyostyly, the mandibular cartilages lack a connection to the cranium. Instead, the hyomandibular cartilages provide the means of jaw support, while the ceratohyal and basihyal elements articulate with the lower jaw. The eyes have a tapetum lucidum, the inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm.
These fish are distributed in tropical and temperate waters. Many fish maintain buoyancy with swim bladders, however elasmobranchs lack swim bladders, and maintain buoyancy instead with large livers that are full of oil. This stored oil may function as a nutrient when food is scarce, deep sea sharks are usually targeted for their oil, because the livers of these species can weigh up to 20% of their total weight. Fossilised shark teeth are known from the early Devonian, around 400 million years ago, during the following Carboniferous period, the sharks underwent a period of diversification, with many new forms evolving