A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus or nautilus. These marine animals are characterized by bilateral body symmetry, a prominent head, a set of arms or tentacles modified from the primitive molluscan foot. Fishermen sometimes call; the study of cephalopods is a branch of malacology known as teuthology. Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids; the class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses and cuttlefish. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Belemnoidea. There are over 800 extant species of cephalopod. An estimated 11,000 extinct taxa have been described, although the soft-bodied nature of cephalopods means they are not fossilised. Cephalopods are found in all the oceans of Earth.
None of them can tolerate freshwater, but the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water. Cephalopods are thought to be unable to live in freshwater due to multiple biochemical constraints, in their +400 million year existence have never ventured into freshwater habitats. Cephalopods occupy most of the depth of the ocean, from the abyssal plain to the sea surface, their diversity is decreases towards the poles. Cephalopods are regarded as the most intelligent of the invertebrates, have well developed senses and large brains; the nervous system of cephalopods is the most complex of the invertebrates and their brain-to-body-mass ratio falls between that of endothermic and ectothermic vertebrates. Captive cephalopods have been known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on the crabs, return to their own aquarium; the brain is protected in a cartilaginous cranium.
The giant nerve fibers of the cephalopod mantle have been used for many years as experimental material in neurophysiology. Many cephalopods are social creatures; some cephalopods are able to fly through the air for distances of up to 50 m. While cephalopods are not aerodynamic, they achieve these impressive ranges by jet-propulsion; the animals spread their fins and tentacles to form wings and control lift force with body posture. One species, Todarodes pacificus, has been observed spreading tentacles in a flat fan shape with a mucus film between the individual tentacles while another, Sepioteuthis sepioidea, has been observed putting the tentacles in a circular arrangement. Cephalopods have advanced vision, can detect gravity with statocysts, have a variety of chemical sense organs. Octopuses use their arms to explore their environment and can use them for depth perception. Most cephalopods rely on vision to detect predators and prey, to communicate with one another. Cephalopod vision is acute: training experiments have shown that the common octopus can distinguish the brightness, size and horizontal or vertical orientation of objects.
The morphological construction gives cephalopod eyes the same performance as sharks'. Cephalopods' eyes are sensitive to the plane of polarization of light. Unlike many other cephalopods, nautiluses do not have good vision, they have a simple "pinhole" eye. Instead of vision, the animal is thought to use olfaction as the primary sense for foraging, as well as locating or identifying potential mates. Given their ability to change color, all octopodes and most cephalopods are considered to be color blind. Coleoid cephalopods have a single photoreceptor type and lack the ability to determine color by comparing detected photon intensity across multiple spectral channels; when camouflaging themselves, they use their chromatophores to change brightness and pattern according to the background they see, but their ability to match the specific color of a background may come from cells such as iridophores and leucophores that reflect light from the environment. They produce visual pigments throughout their body, may sense light levels directly from their body.
Evidence of color vision has been found in the sparkling enope squid, which achieves color vision by the use of three distinct retinal molecules which bind to its opsin. In 2015, a novel mechanism for spectral discrimination in cephalopods was described; this relies on the exploitation of chromatic aberration. Numerical modeling shows that chromatic aberration can yield useful chromatic information through the dependence of image acuity on accommodation; the unusual off-axis slit and annular pupil sha
Squid are cephalopods in the superorder Decapodiformes with elongated bodies, large eyes, eight arms and two tentacles. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, they are soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin. Squid diverged from other cephalopods during the Jurassic and occupy a similar role to teleost fish as open water predators of similar size and behaviour, they play an important role in the open water food web. The two long tentacles are used to grab the eight arms to hold and control it; the beak cuts the food into suitable size chunks for swallowing. Squid are rapid swimmers, moving by jet propulsion, locate their prey by sight, they are among the most intelligent of invertebrates, with groups of Humboldt squid having been observed hunting cooperatively. They are preyed on by sharks, other fish, sea birds and cetaceans sperm whales. Squid can change colour for signalling.
Some species are bioluminescent, using their light for counter-illumination camouflage, while many species can eject a cloud of ink to distract predators. Squid are used for human consumption with commercial fisheries in Japan, the Mediterranean, the southwestern Atlantic, the eastern Pacific and elsewhere, they are used in cuisines around the world known as "calamari". Squid have featured in literature since classical times in tales of giant squid and sea monsters. Squid are members of the class Cephalopoda, subclass Coleoidea; the squid orders Myopsida and Oegopsida are in the superorder Decapodiformes. Two other orders of decapodiform cephalopods are called squid, although they are taxonomically distinct from squids and differ recognizably in their gross anatomical features, they are the bobtail squid of order Sepiolida and the ram's horn squid of the monotypic order Spirulida. The vampire squid, however, is more related to the octopuses than to any squid; the cladogram, not resolved, is based on Sanchez et al, 2018.
Their molecular phylogeny used nuclear DNA marker sequences. If it is accepted that Sepiidae cuttlefish are a kind of squid the squids, excluding the vampire squid, form a clade as illustrated. Orders are shown in boldface. Crown coleoids diverged in the Permian. Squid diverged during the Jurassic. Both the coleoids and the teleost fish were involved in much adaptive radiation at this time, the two modern groups resemble each other in size, habitat and behaviour, however some fish moved into fresh water while the coleoids remained in marine environments; the ancestral coleoid was nautiloid-like with a strait septate shell that became immersed in the mantle and was used for buoyancy control. Four lines diverged from this, the cuttlefishes, the squids and the octopuses. Squid have differentiated from the ancestral mollusc such that the body plan has been condensed antero-posteriorly and extended dorso-ventrally. What may have been the foot of the ancestor is modified into a complex set of appendages around the mouth.
The sense organs are developed and include advanced eyes similar to those of vertebrates. The ancestral shell has been lost, with pen, remaining; the pen, made of a chitin-like material, is a feather-shaped internal structure that supports the squid's mantle and serves as a site for muscle attachment. The cuttlebone or sepion of the Sepiidae is calcareous and appears to have evolved afresh in the Tertiary. Squid are soft-bodied molluscs whose forms have been modified to adopt an active predatory lifestyle; the head and foot of the squid are at one end of a long body, this end is functionally anterior, leading the animal as it moves through the water. The foot has been transformed into a set of eight arms and two distinctive tentacles, which surround the mouth; the suckers may be stalked. Their rims may contain minute toothlike denticles; these features, as well as strong musculature, a small ganglion beneath each sucker to allow individual control, provide a powerful adhesion to grip prey. Hooks are present on the arms and tentacles in some species.
The two tentacles are retractile. Suckers are limited to the spatulate tip of the tentacle, known as the manus. In the mature male, the outer half of one of the left arms is hectocotylised – and ends in a copulatory pad rather than suckers; this is used for depositing a spermatophore inside the mantle cavity of a female. A ventral part of the foot has been converted into a funnel through which water exits the mantle cavity; the main body mass is enclosed in the mantle. These fins are not the main source of locomotion in most species; the mantle wall is muscled and internal. The visceral mass, covered by a thin, membranous epidermis, forms a cone-shaped posterior region known as the "visceral hump"; the mollusc shell is reduced to an internal, longitudinal chitinous "pen" in the functionally dorsal part of the animal. On the functionally ventral part of the body is an opening to the m
Lion's mane jellyfish
The lion's mane jellyfish known as the giant jellyfish or the hair jelly, is the largest known species of jellyfish. Its range is confined to cold, boreal waters of the Arctic, northern Atlantic, northern Pacific Oceans, it is common in the English Channel, Irish Sea, North Sea, in western Scandinavian waters south to Kattegat and Øresund. It may drift into the southwestern part of the Baltic Sea. Similar jellyfish – which may be the same species – are known to inhabit seas near Australia and New Zealand; the largest recorded specimen, found washed up on the shore of Massachusetts Bay in 1870, had a bell with a diameter of 2.3 metres and tentacles 37 m long. Lion's mane jellyfish have been observed below 42°N latitude for some time in the larger bays of the east coast of the United States; the lion's mane jellyfish uses its stinging tentacles to capture, pull in, eat prey such as fish, sea creatures, smaller jellyfish. The taxonomy of the Cyanea species is not agreed upon. Two distinct taxa, occur together in at least the eastern North Atlantic, with the blue jellyfish differing in color and smaller size.
Populations in the western Pacific around Japan are sometimes distinguished as Cyanea nozakii, or as a subspecies, C. c. nozakii. In 2015, Russian researchers announced a possible sister species, Cyanea tzetlinii found in the White Sea, but this has not yet been recognized by other authoritative databases such as WoRMS or ITIS. Lion's mane jellyfish are named for their showy, trailing tentacles reminiscent of a lion's mane, they can vary in size: although capable of attaining a bell diameter of over 2 metres, those found in lower latitudes are much smaller than their far northern counterparts, with a bell about 50 centimetres in diameter. Size seems to dictate coloration: larger specimens are a vivid crimson to dark purple while smaller specimens grade to a lighter orange or tan colorless; the bell of the lion's mane jellyfish is scalloped into eight lobes, each lobe containing from 70 to 150 tentacles, arranged in four distinct rows. Along the bell margin is a balance organ at each of the eight indentations between the lobes – the rhopalium – which helps the jellyfish orient itself.
From the central mouth extend broad frilly oral arms with many stinging cells. Closer to its mouth, its total number of tentacles is around 1200; the long, thin tentacles which emanate from the bell's subumbrella have been characterised as “extremely sticky”. The tentacles of larger specimens may trail as long as 30 m or more, with the tentacles of the longest known specimen measured at 37 m in length; this unusual length – longer than a blue whale – has earned it the status of one of the longest known animals in the world. As coldwater species, these jellyfish cannot cope with warmer waters; the jellyfish are pelagic for most of their lives but tend to settle in shallow, sheltered bays towards the end of their one-year lifespan. In the open ocean, lion's mane jellyfish act as floating oases for certain species, such as shrimp, butterfish and juvenile prowfish, providing both a reliable source of food and protection from predators. Predators of the lion's mane jellyfish include seabirds, larger fish such as ocean sunfish, other jellyfish species, sea turtles.
The leatherback sea turtle feeds exclusively on them in large quantities during the summer season around Eastern Canada. The jellyfish themselves feed on zooplankton, small fish and moon jellies. Lion's mane jellyfish remain very near the surface, at no more than 20 m depth, their slow pulsations drive them forwards weakly, so they depend on ocean currents to travel great distances. The jellyfish are most spotted during the late summer and autumn, when they have grown to a large size and the currents begin to sweep them to shore. Like other jellyfish, lion's manes are capable of both sexual reproduction in the medusa stage and asexual reproduction in the polyp stage. Lion's mane jellyfish have four different stages in their year-long lifespan: a larval stage, a polyp stage, an ephyrae stage, the medusa stage; the female jellyfish carries its fertilized eggs in its tentacle. When the larva are old enough, the female deposits them on a hard surface, where the larva soon grow into polyps; the polyps begin to reproduce asexually.
The individual ephyrae break off the stacks, where they grow into the medusa stage and become full-grown jellyfish. Most encounters cause localized redness. In normal circumstances, in healthy individuals, their stings are not known to be fatal. Vinegar can be used to deactivate the nematocysts, but due to the large number of tentacles, medical attention is recommended after exposure. There may be a significant difference between touching a few tentacles with finger tips at a beach, compared to accidental swimming into one; the initial sensation is more strange than painful and feels like swimming into warmer and somewhat effervescent water. Some minor pains will though soon follow. There is no real danger to humans, but in cases when someone has been stung over large parts of their body by not just the longest tentacles but the entire jellyfish, a visit to a health care centre or similar is recommen
A cnidocyte is an explosive cell containing one giant secretory organelle or cnida that defines the phylum Cnidaria. Cnidae are used for prey defense from predators. Despite being morphologically simple, lacking a skeleton and many species being sessile, cnidarians prey on fish and crustaceans. A cnidocyte fires a structure that contains the toxin, from a characteristic subcellular organelle called a cnidocyst; this is responsible for the stings delivered by a cnidarian. Each cnidocyte contains an organelle called a cnida, nematocyst, ptychocyst or spirocyst; this organelle consists of a bulb-shaped capsule containing a coiled hollow tubule structure attached to it. An immature cnidocyte is referred to as a cnidoblast; the externally oriented side of the cell has a hair-like trigger called a cnidocil, a mechano- and chemo-receptor. When the trigger is activated, the tubule shaft of the cnidocyst is ejected and, in the case of the penetrant nematocyst, the forcefully ejected tubule penetrates the target organism.
This discharge takes no more than a few microseconds, is able to reach accelerations of about 40,000 g. Recent research suggests the process occurs in as little as 700 nanoseconds, thus reaching an acceleration of up to 5,410,000 g. After penetration, the toxic content of the nematocyst is injected into the target organism, allowing the sessile cnidarian to devour the prey; the cnidocyst capsule stores a large concentration of calcium ions, which are released from the capsule into the cytoplasm of the cnidocyte when the trigger is activated. This causes a large concentration gradient of calcium across the cnidocyte plasma membrane; the resulting osmotic pressure causes a rapid influx of water into the cell. This increase in water volume in the cytoplasm forces the coiled cnidae tubule to eject rapidly. Prior to discharge the coiled cnidae tubule exists inside the cell in an "inside out" condition; the back pressure resulting from the influx of water into the cnidocyte together with the opening of the capsule tip structure or operculum, triggers the forceful eversion of the cnidae tubule causing it to right itself as it comes rushing out of the cell with enough force to impale a prey organism.
Since cnidae are "single use" cells, this costs a lot of energy, in order to regulate discharge, cnidocytes are connected as "batteries", containing several types of cnidocytes connected to supporting cells and neurons. The supporting cells contain chemosensors, together with the mechanoreceptor on the cnidocyte, allow only the right combination of stimuli to cause discharge, such as prey swimming, chemicals found in prey cuticle or cuteous tissue; this prevents the cnidarian from stinging itself although sloughed off cnidae can be induced to fire independently. Over 30 types of cnidae are found in different cnidarians, they can be divided into the following groups: Penetrant: The penetrant or stenotele is the largest and most complex nematocyst. When discharged, it pierces the skin or chitinous exoskeleton of the prey and injects the poisonous fluid, that either paralyzes the victim or kills it. Glutinant: a sticky surface used to stick to prey, referred to as ptychocysts and found on burrowing anemones, which help create the tube in which the animal lives Volvent: The volvent or desmoneme is a small and pear-shaped nematocyst.
It contains a short, spineless and elastic thread tube forming a single loop and closed at the far end. When discharged, it coils around the prey, they are the smallest nematocysts. A lasso-like string is fired at prey and wraps around a cellular projection on the prey, which are referred to as spirocysts. Depending on the species, one or several types can appear on the organism; the specific representation of cnidae is referred to as the cnidome of that species and may represent a dynamic aspect of the cnidarian species, responsive to prey availability or the developmental stage of the organism. Nematocysts are efficient weapons. A single nematocyst has been shown to suffice in paralyzing a small arthropod; the most deadly cnidocytes are found on the body of a box jellyfish. One member of this family, the sea wasp, Chironex fleckeri, is "claimed to be the most venomous marine animal known," according to the Australian Institute of Marine Science, it can cause excruciating pain to humans, sometimes followed by death.
Other cnidarians, such as the jellyfish Cyanea capillata or the siphonophore Physalia physalis can cause painful and sometimes fatal stings. On the other hand, aggregating sea anemones may have the lowest sting intensity due to the inability of the nematocysts to penetrate the skin, creating a feeling similar to touching sticky candies. Besides feeding and defense, sea anemone and coral colonies use cnidocytes to sting one another in order to defend or win space. Venom from animals such as cnidarians and spiders may be species-specific. A substance, weakly toxic for humans or other mammals may be toxic to the natural prey or predators of the venomous animal; such specificity has been used to create new medicines and bioinsecticides, biopesticides. Animals in the phylum Ctenophora are transparent and jelly-like but have no nematocysts, are harmless to humans. Certain types of sea slugs, such as the nudibranch aeolids, are known to undergo kleptocnidy, whereby the organisms store nematocysts of digested prey at the tips of their cerat
A hole saw known as a hole cutter, is a saw blade of annular shape, whose annular kerf creates a hole in the workpiece without having to cut up the core material. It is used in a drill. Hole saws have a pilot drill bit at their center to keep the saw teeth from walking; the fact that a hole saw creates the hole without needing to cut up the core makes it preferable to twist drills or spade drills for large holes. The same hole can be made faster and using less power; the depth to which a hole saw can cut is limited by the depth of its cup-like shape. Most hole saws have a short aspect ratio of diameter to depth, they are used to cut through thin workpieces. However, longer aspect ratios are available for applications. Cutting with a hole saw is analogous to some machining operations, called trepanning in the trade, that swing a cutter analogous to a fly cutter in order to achieve a similar result of annular kerf and intact core; the saw consists of a metal cylinder steel, mounted on an arbor. The cutting edge either has industrial diamonds embedded in it.
The arbor can carry a drill bit to bore a centering hole. After the first few millimeters of cut, the centering mechanism may no longer be needed, although it will help the bit to bore without wandering in a deep hole; the sloping slots in the cylinder wall help carry the dust out. The kerf of the cut is designed to be larger than the diameter of the rest of the hole saw so that it does not get jammed in the hole. Holes saws for use with portable drills are available in diameters from 6 to 130 mm, or in the US, ¼ to 6 inches; the only limit on the length of the cylinder, thus depth of the hole, is the need to remove the bit from the hole to clear dust. A 300 mm cylinder length is not uncommon. By breaking the core off from time to time and using a shank extension, a diamond core drill can drill to depths many times its length. Saw teeth are used for most materials, such as wood, soft plaster, metal. Diamond hole saws are used to bore holes in brick, concrete and stone. An adjustable hole saw consists of a number of thin metal saw blade-like strips, a flat disc with a large number of grooves in one side and a shank on the other.
By snapping the blades into different grooves on the disc, a hole saw of a wide variety of sizes can be constructed. Another type of adjustable hole saw called a circle cutter, is formed by having one, two, or three adjustable teeth on a platform with a pilot bit. To cut out a hole of any size, the teeth need only be adjusted to the proper position; this type is available in sizes up to a foot and larger, can be used to cut large circles. The main advantage over conventional drill bits is the hole saw's efficiency, because little of the total material being removed is cut, which reduces the overall power requirement. Another advantage over drill bits is the wider size capability. For example, a 100 millimetres hole would require a huge twist drill or spade drill, unable to be properly driven by a pistol-grip drill or benchtop drill press; some disadvantages include: The portable drill used must be capable of producing considerable torque at low speed They tend to bind if choked with dust, or if allowed to wander away from the central axis of the planned hole The kick-back from a powerful drill may be severe under some conditions, long side-handles should be used, preferably with two operators for large holes.
The core plug binds inside the hole saw, must be pried out after each hole is cut. Sometimes the prying is quite difficult. Sometimes the core plug will twist apart mid-cut, creating a condition where the core inside the hole saw spins on the yet-uncut portion of the core still in the workpiece; this tends to stop the cutting action of the saw, if the workpiece is wood or plastic, the friction will start to singe it, creating a burning smell and heating up the hole saw. The twisted-off core must be pried out of the hole saw before the cutting can continue. Diamond hole saws are called diamond core drill bits. Laser welded diamond core drill bits can be used in wet and dry drilling, but not all materials to be drilled are suitable for dry drilling. Hard materials like reinforced concrete should be drilled with water, otherwise the excessive heat generated during the drilling process may cause the diamonds on the core bit to become blunt, lead to poor drilling performance; the bond materials welded diamond core drill bits are specially adjusted to fit the wet and dry drillings respectively.
This lifespan. Diamond hole saws will drill through tile, porcelain tiles, marble, concrete and any lapidary material
The crown cork, the first form of bottle cap, was invented by William Painter in 1892 in Baltimore. The company making it was called the Bottle Seal Company, but it changed its name with the immediate success of the crown cork to the Crown Cork and Seal Company, it still informally goes by that name, but is Crown Holdings. Crown corks are similar to the Pilfer proof caps; the crown cork was the first successful disposable product. This inspired King C. Gillette to invent the disposable razor; the firm still survives. Prior to the invention of the crown cork bottle stopper, soda bottles had ordinary cork bottle stoppers and had rounded bottoms so they could not be stored standing upright; the reason for this is corks have a tendency to dry out and shrink, which allows the gas pressure in the bottle to cause the cork to "pop." Storing bottles on their side prevents the corks from drying out and "popping." After the invention of the crown cork bottle stopper, this problem was eliminated, soda bottles could be stored standing upright.
Crown corks are collected by people around the world who admire the variety of designs and relative ease of storage. Collectors tend to prefer the term crown cap over corks. In Mexico, these are called corcholatas. In Spain and South America, the names chapas or chapitas are used. In the Philippines, the term tansan is employed. Bottle cap Bottle opener Flip-top Live Counter of produced crown corks U. S. Patent 468,226 U. S. Patent 468,258 Bottle Cap Index Davide's Crown Caps Homepage Collection of Alex and Gemma
Caecilians are a group of limbless, serpentine amphibians. They live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. All modern caecilians and their closest fossil relatives are grouped as a clade, within the larger group Gymnophiona, which includes more primitive extinct caecilian-like amphibians. Caecilians are distributed in the tropics of South and Central America and southern Asia, their diet consists of small subterranean creatures such as earthworms. Caecilians lack limbs, making the smaller species resemble worms, while the larger species, with lengths up to 1.5 m, resemble snakes. Their tails are short or absent, their cloacae are near the ends of their bodies, their skin is smooth and dark, but some species have colourful skins. Inside the skin are calcite scales; because of these scales, the caecilians were once thought to be related to the fossil Stegocephalia, but they are now believed to be a secondary development, the two groups are most unrelated.
The skin has numerous ring-shaped folds, or annuli, that encircle the body, giving them a segmented appearance. Like some other living amphibians, the skin contains glands; the skin secretions of Siphonops paulensis have been shown to have hemolytic properties. Caecilians' vision is limited to dark-light perception, their anatomy is adapted for a burrowing lifestyle, they have a strong skull, with a pointed snout used to force their way through mud. In most species, the bones in the skull are reduced in number and fused together, the mouth is recessed under the head, their muscles are adapted to pushing their way through the ground, with the skeleton and deep muscles acting as a piston inside the skin and outer muscles. This allows the animal to anchor its hind end in position, force the head forwards, pull the rest of the body up to reach it in waves. In water or loose mud, caecilians instead swim in an eel-like fashion. Caecilians in the family Typhlonectidae are aquatic, the largest of their kind.
The representatives of this family have a fleshy fin running along the rear section of their bodies, which enhances propulsion in water. All but the most primitive caecilians have two sets of muscles for closing the jaw, compared with the single pair found in other creatures; these are more developed in the most efficient burrowers among the caecilians, appear to help keep the skull and jaw rigid. All caecilians possess a pair of tentacles located between their nostrils; these are used for a second olfactory capability, in addition to the normal sense of smell based in the nose. The middle ear consists of only the stapes and the oval window, which transfer vibration to the inner ear through a reentrant fluid circuit as seen in some reptiles; the species within the Scolecomorphidae lack both stapes and an oval window, making them the only known amphibians missing all the components of a middle ear apparatus. Except for one lungless species, Atretochoana eiselti, all caecilians have lungs, but use their skin or mouths for oxygen absorption.
The left lung is much smaller than the right one, an adaptation to body shape, found in snakes. Caecilians are found in wet, tropical regions of Southeast Asia, Bangladesh and Sri Lanka, parts of East and West Africa, the Seychelles Islands in the Indian Ocean, Central America, in northern and eastern South America. In Africa, caecilians are found from Guinea-Bissau to southern Malawi, with an unconfirmed record from eastern Zimbabwe, they have not been recorded from the extensive areas of tropical forest in central Africa. In South America, they extend through subtropical eastern Brazil well into temperate northern Argentina, they can be seen as far south as Buenos Aires, when they are carried by the flood waters of the Paraná River coming from farther north. Their American range extends north to southern Mexico; the northernmost distribution is of the species Ichthyophis sikkimensis of northern India. Ichthyophis is found in South China and North Vietnam. In Southeast Asia, they are found as far east as Java and the southern Philippines, but they have not crossed Wallace's line and are not present in Australia or nearby islands.
The name caecilian derives from the Latin word caecus, meaning "blind", referring to the small or sometimes nonexistent eyes. The name dates back to the taxonomic name of the first species described by Carl Linnaeus, which he named Caecilia tentaculata. There has been disagreement over the use of the two primary scientific names for caecilians and Gymnophiona; some specialists prefer to use the name Gymnophiona to refer to the "crown group", that is, the group containing all modern caecilians and extinct members of these modern lineages. They sometimes use the name Apoda to refer to the total group, that is, all caecilians and caecilian-like amphibians that are more related to modern groups than to frogs or salamanders. However, many scientists have advocated for the reverse arrangement, where Apoda is used as the name for modern caecilian groups; some have argued that this use makes more sense, because the name "Apoda" means "without feet", this is a feature associated with modern species. The most recent classification of caecilians, by Wilkinson et al. divided the caecilians into 9 families containing nearly 200 species.
Since a tenth caecilian family has been discovered, Chikilidae. This classification is based on a thorough definition of monophyly based on morphological and molecular