A helix is a type of smooth space curve, i. e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a line called the axis. Examples of helices are coil springs and the handrails of spiral staircases, a filled-in helix – for example, a spiral ramp – is called a helicoid. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, and many proteins have helical substructures, known as alpha helices, the word helix comes from the Greek word ἕλιξ, curved. Helices can be either right-handed or left-handed, handedness is a property of the helix, not of the perspective, a right-handed helix cannot be turned to look like a left-handed one unless it is viewed in a mirror, and vice versa. Most hardware screw threads are right-handed helices, the alpha helix in biology as well as the A and B forms of DNA are right-handed helices. The Z form of DNA is left-handed, the pitch of a helix is the height of one complete helix turn, measured parallel to the axis of the helix. A double helix consists of two helices with the axis, differing by a translation along the axis.
A conic helix may be defined as a spiral on a conic surface, an example is the Corkscrew roller coaster at Cedar Point amusement park. A circular helix, has constant band curvature and constant torsion, a curve is called a general helix or cylindrical helix if its tangent makes a constant angle with a fixed line in space. A curve is a general helix if and only if the ratio of curvature to torsion is constant, a curve is called a slant helix if its principal normal makes a constant angle with a fixed line in space. It can be constructed by applying a transformation to the frame of a general helix. Some curves found in nature consist of multiple helices of different handedness joined together by transitions known as tendril perversions, in mathematics, a helix is a curve in 3-dimensional space. The following parametrisation in Cartesian coordinates defines a particular helix, Probably the simplest equations for one is x = cos , y = sin , z = t. As the parameter t increases, the point traces a right-handed helix of pitch 2θ and radius 1 about the z-axis, in cylindrical coordinates, the same helix is parametrised by, r =1, θ = t, h = t. A circular helix of radius a and slope b/a is described by the following parametrisation, another way of mathematically constructing a helix is to plot the complex-valued function exi as a function of the real number x.
The value of x and the real and imaginary parts of the function value give this plot three real dimensions, except for rotations and changes of scale, all right-handed helices are equivalent to the helix defined above. The equivalent left-handed helix can be constructed in a number of ways, in music, pitch space is often modeled with helices or double helices, most often extending out of a circle such as the circle of fifths, so as to represent octave equivalency
The decollate snail, scientific name Rumina decollata, is a medium-sized predatory land snail, a species of terrestrial pulmonate gastropod mollusk in the family Subulinidae. It is a European species that has introduced in a number of areas worldwide. This species is native to the Mediterranean excluding south-east Mediterranean and it is introduced in Israel and in Egypt since Roman times. It has been introduced into North America, including Phoenix and Glendale, Arizona and it is found in Great Britain, as a hothouse alien The shell of the decollate snail is long and roughly cone-shaped. Rumina decollata is a predator, and feeds readily upon common garden snails and slugs. The snail eats plant matter as well, but the damage it causes to plants is considered minor when compared with the benefit of its predation on garden snails, unfortunately it will consume harmless local species of land gastropods, and beneficial annelids. Decollate snails are tolerant of dry and cold conditions, during which they burrow deep into the soil and they are most active during the night and during rainfall.
Rumina decollata on the UF / IFAS — Featured Creatures website, a photo of decollates feeding on Helix
Charonia is a genus of very large sea snail, commonly known as Tritons trumpet or Triton Snail. They are marine gastropod mollusks in the family Ranellidae, the common name Tritons trumpet is derived from the Greek god Triton, who was the son of Poseidon, god of the sea. The god Triton is often portrayed blowing a large seashell horn similar to this species and this genus is known in the fossil records from the Cretaceous to the Quaternary. Fossils are found in the marine strata throughout the world, species within the genus Charonia have large fusiform shells, usually whithish with brown or yellow markings. The shell of the giant triton Charonia tritonis, which lives in the Indo-Pacific faunal zone, one slightly smaller (shell size 100–385 millimetres but still very large species, Charonia variegata, lives in the western Atlantic, from North Carolina to Brazil. Charonia species inhabit temperate and tropical waters worldwide, unlike pulmonate and opistobranch gastropods, tritons are not hermaphrodites, they have separate sexes and undergo sexual reproduction with internal fertilization.
The female deposits white capsules in clusters, each of which contains many developing larvae, the larvae emerge free-swimming and enter the plankton, where they drift in open water for up to three months. Adult tritons are active predators and feed on molluscs and starfish. The giant triton has gained fame for its ability to capture and eat crown-of-thorns starfish, Tritons can be observed to turn and give chase when the scent of prey is detected. Some starfish appear to be able to detect the approach of the mollusc by means which are not clearly understood, and they will attempt flight before any physical contact has taken place. Tritons, are faster than starfish, and only large starfish have a hope of escape. The triton grips its prey with its foot and uses its toothy radula to saw through the starfishs armoured skin. Once it has penetrated, a paralyzing saliva subdues the prey, Tritons ingest smaller prey animals whole without troubling to paralyse them, and will spit out any poisonous spines, shells, or other unwanted parts later.
Many people find triton shells attractive as an object, and so they are collected. In recent years this has contributed to the animals scarcity, from ancient times, people of many different cultures have removed the tip of the shell, or drilled a hole in the tip, and used the shell as a trumpet. The Greco-Roman god Poseidon / Neptune is often depicted holding a triton shell, indo-West Pacific Ranellidae and Personidae. A monograph of the New Caledonian fauna and revisions of related taxa, mémoires du Muséum national dHistoire naturelle 178, 1-255 An article on the crown-of-thorns starfish which contains excellent pictures of one being eaten by a triton
Ammonoids are an extinct group of marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs are more related to living coleoids than they are to shelled nautiloids such as the living Nautilus species. The earliest ammonites appear during the Devonian, and the last species died out during the Cretaceous–Paleogene extinction event, Ammonites are excellent index fossils, and it is often possible to link the rock layer in which a particular species or genus is found to specific geologic time periods. Their fossil shells usually take the form of planispirals, although there were some helically spiraled and nonspiraled forms, the name ammonite, from which the scientific term is derived, was inspired by the spiral shape of their fossilized shells, which somewhat resemble tightly coiled rams horns. Pliny the Elder called fossils of these animals ammonis cornua because the Egyptian god Ammon was typically depicted wearing rams horns, often the name of an ammonite genus ends in -ceras, which is Greek for horn.
The topology of the septa, especially around the rim, results in the various suture patterns found, three major types of suture patterns are found in the Ammonoidea, Goniatitic - numerous undivided lobes and saddles, typically 8 lobes around the conch. This pattern is characteristic of the Paleozoic ammonoids, ceratitic - lobes have subdivided tips, giving them a saw-toothed appearance, and rounded undivided saddles. This suture pattern is characteristic of Triassic ammonoids and appears again in the Cretaceous pseudoceratites, ammonitic - lobes and saddles are much subdivided, subdivisions are usually rounded instead of saw-toothed. Ammonoids of this type are the most important species from a point of view. This suture type is characteristic of Jurassic and Cretaceous ammonoids, the siphuncle in most ammonoids by far is a narrow tubular structure that runs along the outer rim, known as the venter, connecting the chambers of the phragmocone to the body or living chamber. This distinguishes them from living nautiloides and typical Nautilida, the word siphuncle comes from the New Latin siphunculus, meaning little siphon.
Originating from within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Devonian, while nearly all nautiloids show gently curving sutures, the ammonoid suture line is variably folded, forming saddles and lobes. In subsequent taxonomies, these are regarded as orders within the subclass Ammonoidea. Because ammonites and their relatives are extinct, little is known about their way of life. Their soft body parts are rarely preserved in any detail. Nonetheless, much has been worked out by examining ammonoid shells, synchrotron analysis of an aptychophoran ammonite revealed remains of isopod and mollusc larvae in its buccal cavity, indicating at least this kind of ammonite fed on plankton. They may have avoided predation by squirting ink, much like modern cephalopods, the soft body of the creature occupied the largest segments of the shell at the end of the coil. The smaller earlier segments were walled off and the animal could maintain its buoyancy by filling them with gas, the smaller sections of the coil would have floated above the larger sections
The columella or pillar is a central anatomical feature of a coiled snail shell, a gastropod shell. The columella is often clearly visible as a structure when the shell is broken, sliced in half vertically. The columella runs from the apex of the shell to the midpoint of the undersurface of the shell, or the tip of the siphonal canal in those shells which have a siphonal canal. If a snail shell is visualized as a cone of shelly material which is wrapped around a central axis, in the case of shells that have an umbilicus, the columella is a hollow structure. The columella of some groups of shells can have a number of plications or folds. These folds can be wide or narrow, prominent or subtle and these features of the columella are often useful in identifying the family, genus, or species of the gastropod. The surface of the columella is called the columellar wall, the columellar callus is a smooth, calcareous thickening, secreted by the mantle, extending over the columellar area. The columellar lip, the part of the columella, is the lower part of the inner lip and is situated near the axis of coiling. A columellar tooth is a projection on the inner lip of a columella in the direction of the aperture.
The soft parts of the body of the gastropod are held in place in the shell by the columellar muscles. These muscles are attached strongly to the columella itself not just far up in the apex of the shell but by a long and narrow attachment over the length of a full whorl along the columella. The columellar muscle passes underneath the mantle, greatly thickening the body wall, the columellar muscles are contracted when the animal needs to withdraw the foot and other soft parts into the shell for protection from drying out, and from predators. During these contractions the operculum and shell are approximated, and the animal is withdrawn within the latter, the columellar muscles are equally used to bring the soft body out of the shell. During protraction and retraction, the twists, shortens or elongates. In very large such as the Queen Conch, Eustrombus gigas, once the columellar muscles are cut with a knife. Conch fishermen in the Caribbean Sea break a hole in the spire of the shell, cut the columellar muscles.
Often the fishermen dump the empty back into the sea again. Columella listed in a glossary Another glossary A scholarly article on columellar muscles and columellar folds photo of cross section through shells
Physa is a genus of small, left-handed or sinistral, air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Physidae. These snails eat algae and detritus, members of the freshwater pulmonate family Physidae possess a complex of muscles that is unique amongst gastropods. This complex was given the name physid musculature, the physid musculature has two main components, the physid muscle sensu stricto and the fan muscle. The physid musculature is responsible for an ability of physids to rapidly flick their shells from side to side — a reaction that frequently enables them to escape predation. The shells of Physa species have a long and large aperture, a pointed spire, the shells are thin and corneous, and rather transparent. Lake Winnipeg Physa, lives in Manitoba in Canada and it was classified as endangered by COSEWIC. ‘’The young specialist looks at land and freshwater molluscs’’, http, //www. animalbase. uni-goettingen. de/zooweb/servlet/AnimalBase/list/species. taxongenus=301 Dillon R. T.
Wethington A. R. & Lydeard C. The evolution of reproductive isolation in a simultaneous hermaphrodite, the freshwater snail Physa
Turbo is a genus of large sea snails with gills and an operculum, marine gastropod molluscs in the family Turbinidae, the turban snails. Turbo is the genus of the family. Species in this genus have an aperture and a solid. This circular operculum commences as a disc, like that of a Trochus. The radula is broad and generally rather short, the median and marginal teeth are always present, and the formula is invariably ∞.5.1.5. ∞. The central teeth contain no cusps, frequently the central teeth are asymmetrical in this group. The laterals bear supporting wings at their angles, and are various in form. The inner marginals are very large, with large cusps, the first Turbo species were found in the Upper Cretaceous, approximately 100 million years ago. According to Alf et al. the genus Turbo is divided in 16 Recent subgenera, the number of presently known living species in Turbo is 66, plus five subspecies. Turbo cornutus, common name the turban, is an expensive food item in Korea, and Japan. The attractively colored operculum of at least two different Turbo species has been used for decorative purposes, including in jewelry and buttons.
These opercula are sometimes known as cats eyes
The shell of this species appears to be dextral in coiling, even though it is in fact sinistral or left-handed. For terms see gastropod shell All species within family Planorbidae have sinistral shells, Planorbarius corneus is the largest European species of ramshorn snail, with a shell typically measuring 35 millimetres across when fully-grown. The 10–17 by 22–40 millimetres coiled shell has between 3 and 4.5 rounded whorls with deep sutures, the last whorl predominating, the upper side is weakly depressed and the lower side is deeply depressed. The shell is yellowish with a brown, reddish or greenish periostracum. The aperture is wide and almost circular, the animal is brown or reddish. Planorbarius corneus is distributed from western Europe, through central Europe and into the Caucasus, north into Siberia, in western Europe, it has been recorded in Belgium and the British Isles. It is not found in Spain, but it has recorded on some Spanish and Portuguese Atlantic islands, including Madeira, the Azores.
In the Nordic countries, it has recorded in Denmark, Sweden. Its range extends through central Europe into southern Europe and eastern Europe, the species is found in western Asia, having been recorded in Kazakhstan, western regions of Russia, Turkey and Uzbekistan. Additionally, as the species is sold in the aquarium trade. Planorbarius corneus under high temperatures has been studied by Kartavykh & Podkovkin, self-fertilization is possible, one single released animal can establish a stable population, but only 5% of the juveniles in self-fertilized eggs will hatch. G. Checklist of New Zealand living Mollusca, Planorbarius corneus at Animalbase taxonomy, short description, biology, images Planorbarius corneus. Planorbarius corneus images at Consortium for the Barcode of Life Pesticides Database - Chemical Toxicity Studies
A cephalopod is any member of the molluscan class Cephalopoda. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, fishermen sometimes call them inkfish, referring to their common ability to squirt ink. The study of cephalopods is a branch of known as teuthology. Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids, the class now contains two, only distantly related, extant subclasses, which includes octopuses and cuttlefish, and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the shell has been internalized or is absent, whereas in the Nautiloidea. About 800 living species of cephalopods have been identified, two important extinct taxa are the Ammonoidea and Belemnoidea. There are over 800 extant species of cephalopod, although new species continue to be described, an estimated 11,000 extinct taxa have been described, although the soft-bodied nature of cephalopods means they are not easily 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 due to multiple biochemical constraints. Cephalopods occupy most of the depth of the ocean, from the plain to the sea surface. Their diversity is greatest near the equator and decreases towards the poles, Cephalopods are widely regarded as the most intelligent of the invertebrates, and have well developed senses and large brains. The nervous system of cephalopods is the most complex of the invertebrates, the brain is protected in a cartilaginous cranium. Cephalopods have known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on the crabs. Cephalopods are social creatures, when isolated from their own kind, some cephalopods are able to fly through the air for distances of up to 50 m.
While cephalopods are not particularly aerodynamic, they achieve these impressive ranges by jet-propulsion, the animals spread their fins and tentacles to form wings and actively control lift force with body posture. Cephalopods have advanced vision, can detect gravity with statocysts, and have a variety of 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, and to communicate with one another. Consequently, cephalopod vision is acute, training experiments have shown that the octopus can distinguish the brightness, shape
Xerolenta obvia is a species of air-breathing land snail, a terrestrial gastropod mollusk in the family Hygromiidae, the hairy snails and their allies. This land snail occurs in European countries including Bulgaria, Czech Republic, Poland, Ukraine, United States of America and others. This species in the USA is considered to represent a serious threat as a pest. Therefore it has suggested that this species be given top national quarantine significance in the USA. Shells of Xerolenta obvia are medium-sized and relatively flat, in the adult stage,5 to 6 turns are present. These shells are thick and smooth, with a white or yellowish-white basic color and quite variable. The size of the egg is 1.5 mm