1.
Bivalvia
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Bivalves as a group have no head and they lack some usual molluscan organs like the radula and the odontophore. They include the clams, oysters, cockles, mussels, scallops, the gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment where they are safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces, some bivalves, such as the scallops and file shells, can swim. The shipworms bore into wood, clay, or stone and live inside these substances, the shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. These are joined together along one edge by a ligament that, usually in conjunction with interlocking teeth on each of the valves. This arrangement allows the shell to be opened and closed without the two halves detaching, the shell is typically bilaterally symmetrical, with the hinge lying in the sagittal plane. Adult shell sizes of bivalves vary from fractions of a millimetre to over a metre in length, Bivalves have long been a part of the diet of coastal and riparian human populations. Oysters were cultured in ponds by the Romans, and mariculture has more become a important source of bivalves for food. Modern knowledge of molluscan reproductive cycles has led to the development of hatcheries, a better understanding of the potential hazards of eating raw or undercooked shellfish has led to improved storage and processing. Pearl oysters are the most common source of natural pearls, the shells of bivalves are used in craftwork, and the manufacture of jewellery and buttons. Bivalves have also used in the biocontrol of pollution. Bivalves appear in the record first in the early Cambrian more than 500 million years ago. The total number of living species is about 9,200 and these species are placed within 1,260 genera and 106 families. Marine bivalves represent about 8,000 species, combined in four subclasses and 99 families with 1,100 genera, the largest recent marine families are the Veneridae, with more than 680 species and the Tellinidae and Lucinidae, each with over 500 species. The freshwater bivalves include seven families, the largest of which are the Unionidae, the taxonomic term Bivalvia was first used by Linnaeus in the 10th edition of his Systema Naturae in 1758 to refer to animals having shells composed of two valves. More recently, the class was known as Pelecypoda, meaning axe-foot, the name bivalve is derived from the Latin bis, meaning two, and valvae, meaning leaves of a door. Bivalves vary greatly in overall shape, some, such as the cockles, have shells that are nearly globular, cockles can jump by bending and straightening their foot
2.
False angelwing
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Petricolaria pholadiformis closely resembles the angel wing, the main distinguishing feature being that it lacks the apophyses, the spoon-shaped wings located near the beak, of the real angel wing. It grows to about 5 centimetres long and is usually white, the anterior end is extended and has a rounded point while the posterior end is blunt and curved. There are ridges radiating from the beak, which are pronounced at the posterior end. This species is native to the Eastern Coast of North America including the Gulf of Mexico and this clam was introduced and has become established in the British Isles, and on the West Coast of North America
3.
Bivalve shell
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A bivalve shell is part of the body, the exoskeleton or shell, of a bivalve mollusk. In life, the shell of this class of mollusks is composed of two hinged parts or valves, bivalves are very common in essentially all aquatic locales, including saltwater, brackish water, and freshwater. The shells of bivalves commonly wash up on beaches and along the edges of lakes, rivers, bivalves by definition possess two shells or valves, a right valve and a left valve, that are joined by a ligament. The two valves usually articulate with one another using structures known as teeth which are situated along the hinge line, if symmetrical front-to-back, the valves are said to be equilateral, and are otherwise considered inequilateral. This exoskeleton serves not only for muscle attachment, but also for protection from predators, the shell has several layers, and is typically made of calcium carbonate precipitated out into an organic matrix. It is secreted by a part of the body known as the mantle. The bivalve shell is composed of two calcareous valves, the mantle, a thin membrane surrounding the body, secretes the shell valves, ligament, and hinge teeth. The mantle lobes secrete the valves, and the mantle crest creates the other parts, the mantle itself is attached to the shell by numerous small mantle retractor muscles, which are arranged in a narrow line along the length of the interior of the shell. The adductor muscles are what allow the bivalve to close the shell tightly, in some bivalves the mantle edges fuse to form siphons, which take in and expel water during suspension feeding. Species which live buried in sediment usually have long siphons, and when the needs to close its shell. This feature of the anatomy of a bivalve is clearly indicated on the interior of the shell surface as a pallial sinus. The outermost layer of the shell is known as the periostracum and is composed of an organic substance. This sometimes forms a yellowish or brownish skin on the outside of the shell, the periostracum may start to peel off of a shell when the shell is allowed to dry out for long periods. The shell is added to, and increases in size, in two ways - by increments added to the edge of the shell, and by a gradual thickening throughout the animals life. The two shell valves are held together at the animals dorsum by the ligament, which is composed of the tensilium and resilium, in life the ligament opens the shell, and the adductor muscle or muscles close the shell. When a bivalve dies, its adductor muscle relax and the resilium pushes the valves open, in many species of cemented bivalves, the lower valve is more deeply cupped than the upper valve, which tends to be rather flat. In some groups of cemented bivalves the lower or cemented valve is the left valve, the oldest point of a bivalve shell is called the beak, and the raised area around it is known as the umbo. The hinge area is the dorsum or back of the shell, the lower, curved margin is the ventral side
4.
Land snail
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A land snail is any of the numerous species of snail that live on land, as opposed to sea snails and freshwater snails. Land snail is the name for terrestrial gastropod mollusks that have shells. The majority of land snails are pulmonates and that is, they have a lung and breathe air. A minority however belong to more ancient lineages where their anatomy includes a gill. Many of these land snails live in habitats or microhabitats that are sometimes damp or wet. Land snails have a muscular foot, they use mucus to enable them to crawl over rough surfaces. Like other mollusks, land snails have a mantle, and they have one or two pairs of tentacles on their head and their internal anatomy includes a radula and a primitive brain. In terms of reproduction, the majority of land snails are hermaphrodite, tiny snails hatch out of the egg with a small shell in place, and the shell grows spirally as the soft parts gradually increase in size. Most land snails have shells that are right-handed in their coiling, Land snails move by gliding along on their muscular foot, which is lubricated with mucus and covered with epithelial cilia. This motion is powered by succeeding waves of contractions that move down the ventral of the foot. This muscular action is visible when a snail is crawling on the glass of a window or aquarium. Snails move at a low speed. Snails secrete mucus externally to keep their bodies from drying out. The mucus that land snails secrete with the leaves a slime trail behind them. Snails also have a mantle, a layer of tissue which covers all of the internal organs as they are grouped together in the visceral mass. The mantle also extends outward in flaps which reach to the edge of the shell and in some cases can cover the shell, the mantle is attached to the shell, and creates the shell and makes shell growth possible by secretion. A lack of calcium, or low pH in their surroundings, can result in thin, cracked, usually a snail can repair damage to its shell over time if its living conditions improve, but severe damage can be fatal. When retracted into their shells, many snails with gills are able to protect themselves with a door-like anatomical structure called an operculum, Land snails range greatly in size
5.
Arianta arbustorum
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Arianta arbustorum is a medium-sized species of land snail, sometimes known as the copse snail, a terrestrial pulmonate gastropod mollusk in the family Helicidae. One of the most frequent species of snails in Switzerland, can be very abundant. In Finland, it has become so common in the Porvoo region east of Helsinki, estonia Latvia scattered to Serbia Bulgaria It is rare in Bulgaria. Therefore, it has suggested that this species be given top national quarantine significance in the USA. The shell has 5-5.5 convex whorls with deep suture, the last whorl is slightly descending near the aperture. The aperture is with prominent white lip inside, umbilicus is entirely covered by the reflected columellar margin. The width of the shell is 18–25 mm, the height of the shell is 12–22 mm. Arianta arbustorum lives in forests and open habitats of any kind and it lives also in disturbed habitats. It may locally tolerate non-calcareous substrate, in north Scotland also on sandhills, in the Alps up to 2700 m, in Britain 1200 m, in Bulgaria 1500 m. It feeds on herbs, dead animals and faeces. If snails hatched more than 50 m distant from other, they are considered isolated since they would not move more than 25 m, usually they move about 7–12 m in a year. This species of snail makes and uses love darts during mating. Reproduction is usually after copulation, but self-fertilization is also possible, the size of the egg is 3.2 mm. Maturity is reached after 2–4 years. The maximum age up to 14 years, angiostrongylus vasorum has successfully experimentally infected this snail. This article incorporates public domain text from the reference, Arianta arbustorum at Animalbase taxonomy, short description, distribution, biology, status, images Arianta arbustorum images at Encyclopedia of Life Arianta arbustorum. Baur, Anette, Baur, Bruno Interpopulation variation in the prevalence and intensity of parasitic infection in the land snail Arianta arbustorum, Invertebrate Biology, Vol.124 Issue 3. Baur, Bruno & Locher Rolf Sperm allocation in the simultaneously hermaphroditic land snail Arianta arbustorum, oct98, Vol.56 Issue 4, p839. Baur, Bruno Patterns of dispersion, density and dispersal in alpine populations of the land snail Arianta arbustorum, mai 1986, Vol.9 Issue 2, p117-125
6.
Exoskeleton
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An exoskeleton is the external skeleton that supports and protects an animals body, in contrast to the internal skeleton of, for example, a human. In usage, some of the kinds of exoskeletons are known as shells. Examples of animals with exoskeletons include insects such as grasshoppers and cockroaches, the shells of certain sponges and the various groups of shelled molluscs, including those of snails, clams, tusk shells, chitons and nautilus, are also exoskeletons. Some animals, such as the tortoise, have both an endoskeleton and an exoskeleton, exoskeletons have a role in defense from pests and predators, support, and in providing an attachment framework for musculature. Exoskeletons contain chitin, the addition of calcium carbonate makes them harder and stronger, ingrowths of the arthropod exoskeleton known as apodemes serve as attachment sites for muscles. These structures are composed of chitin, and are six times as strong. Similar to tendons, apodemes can stretch to store energy for jumping. Many different species produce exoskeletons, which are composed of a range of materials, bone, cartilage, or dentine is used in the Ostracoderm fish and turtles. Chitin forms the exoskeleton in arthropods including insects, arachnids such as spiders, crustaceans such as crabs and lobsters, calcium carbonates constitute the shells of molluscs, brachiopods, and some tube-building polychaete worms. Silica forms the exoskeleton in the microscopic diatoms and radiolaria, one species of mollusc, the scaly-foot gastropod, even makes use of the iron sulfides greigite and pyrite. Some organisms, such as some foraminifera, agglutinate exoskeletons by sticking grains of sand, contrary to a common misconception, echinoderms do not possess an exoskeleton, as their test is always contained within a layer of living tissue. Exoskeletons have evolved many times,18 lineages evolved calcified exoskeletons alone. Further, other lineages have produced tough outer coatings analogous to an exoskeleton and this coating is constructed from bone in the armadillo, and hair in the pangolin. The armor of reptiles like turtles and Ankylosaurs is constructed of bone, crocodiles have bony scutes, since exoskeletons are rigid, they present some limits to growth. Organisms with open shells can grow by adding new material to the aperture of their shell, as is the case in snails, bivalves, a true exoskeleton, like that found in arthropods, must be shed when it is outgrown. A new exoskeleton is produced beneath the old one, as the old one is shed, the new skeleton is soft and pliable. The animal will pump itself up to expand the new shell to maximal size, when the shell has set, the empty space inside the new skeleton can be filled up as the animal eats. Failure to shed the exoskeleton once outgrown can result in the animal being suffocated within its own shell and this is the mechanism behind some insect pesticides, such as Azadirachtin
7.
Phylum
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In biology, a phylum is a taxonomic rank below kingdom and above class. Traditionally, in botany the term division was used instead of phylum, although from 1993 the International Code of Nomenclature for algae, fungi, depending on definitions, the kingdom Animalia contains approximately 35 phyla, Plantae contains about 12, and Fungi contains around 7. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta, the definitions of zoological phyla have changed from their origins in the six Linnaean classes and the four embranchements of Georges Cuvier. Haeckel introduced the term phylum, based on the Greek word phylon, in plant taxonomy, Eichler classified plants into five groups, named divisions. Informally, phyla can be thought of as grouping organisms based on general specialization of body plan, the most important objective measure in the above definitions is the certain degree—how unrelated do organisms need to be to be members of different phyla. The minimal requirement is that all organisms in a phylum should be more closely related to one another than to any other group. So phyla can be merged or split if it becomes apparent that they are related to one another or not, a definition of a phylum based on body plan has been proposed by paleontologists Graham Budd and Sören Jensen. By Budd and Jensens definition, a phylum is defined by a set of shared by all its living representatives. This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members, also, this definition is based on an arbitrary point of time, the present. However, as it is based, it is easy to apply to the fossil record. A greater problem is that it relies on a decision about which groups of organisms should be considered as phyla. However, proving that a fossil belongs to the group of a phylum is difficult. Furthermore, organisms in the group of a phylum can possess the body plan of the phylum without all the characteristics necessary to fall within it. This weakens the idea that each of the phyla represents a body plan. A classification using this definition may be affected by the chance survival of rare groups. Representatives of many modern phyla did not appear until long after the Cambrian, the kingdom Plantae is defined in various ways by different biologists. All definitions include the living embryophytes, to which may be added the two green algae divisions, Chlorophyta and Charophyta, to form the clade Viridiplantae. The table below follows the influential Cavalier-Smith system in equating Plantae with Archaeplastida, a group containing Viridiplantae, the definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years
8.
Mollusca
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The molluscs compose the large phylum Mollusca of invertebrate animals. Around 85,000 extant species of molluscs are recognized, molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats and they are highly diverse, not just in size and in anatomical structure, but also in behaviour and in habitat. The phylum is divided into 9 or 10 taxonomic classes. The gastropods are by far the most numerous molluscs in terms of classified species, the three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula, and the structure of the nervous system. Other than these things, molluscs express great morphological diversity, so many textbooks base their descriptions on an ancestral mollusc. This has a single, limpet-like shell on top, which is made of proteins and chitin reinforced with calcium carbonate, the underside of the animal consists of a single muscular foot. Although molluscs are coelomates, the coelom tends to be small, the main body cavity is a hemocoel through which blood circulates, their circulatory systems are mainly open. The generalized mollusc has two paired nerve cords, or three in bivalves, the brain, in species that have one, encircles the esophagus. Most molluscs have eyes, and all have sensors to detect chemicals, vibrations, the simplest type of molluscan reproductive system relies on external fertilization, but more complex variations occur. All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, good evidence exists for the appearance of gastropods, cephalopods and bivalves in the Cambrian period 541 to 485.4 million years ago. Molluscs have, for centuries, also been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye and their shells have also been used as money in some preindustrial societies. Mollusc species can also represent hazards or pests for human activities, the bite of the blue-ringed octopus is often fatal, and that of Octopus apollyon causes inflammation that can last for over a month. Stings from a few species of large tropical cone shells can also kill, schistosomiasis is transmitted to humans via water snail hosts, and affects about 200 million people. Snails and slugs can also be serious pests, and accidental or deliberate introduction of some snail species into new environments has seriously damaged some ecosystems. The words mollusc and mollusk are both derived from the French mollusque, which originated from the Latin molluscus, from mollis, molluscus was itself an adaptation of Aristotles τα μαλακά, the soft things, which he applied to cuttlefish. The scientific study of molluscs is accordingly called malacology, as it is now known these groups have no relation to molluscs, and very little to one another, the name Molluscoida has been abandoned. The most universal features of the structure of molluscs are a mantle with a significant cavity used for breathing and excretion
9.
Snail
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Snail is a common name that is applied most often to land snails, terrestrial pulmonate gastropod molluscs. However, the common name snail is also applied to most of the members of the molluscan class Gastropoda that have a shell that is large enough for the animal to retract completely into. When the word snail is used in this most general sense, it not just land snails but also thousands of species of sea snails. Occasionally a few other molluscs that are not actually gastropods, such as the Monoplacophora, snail-like animals that naturally lack a shell, or have only an internal shell, are mostly called slugs, and land snails that have only a very small shell are often called semi-slugs. Even a few species have lungs. Snails can be found in a wide range of environments, including ditches, deserts. Although land snails may be familiar to laymen, marine snails constitute the majority of snail species, and have much greater diversity. Numerous kinds of snail can also be found in fresh water, most snails have thousands of microscopic tooth-like structures located on a banded ribbon-like tongue called a radula. The radula works like a file, ripping food into small pieces, many snails are herbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species are omnivores or predatory carnivores. Several species of the genus Achatina and related genera are known as giant African land snails, some grow to 15 in from snout to tail, and weigh 1 kg. The largest living species of sea snail is Syrinx aruanus, its shell can measure up to 90 cm in length, and the whole animal with the shell can weigh up to 18 kg. The snail Lymnaea makes decisions by using two types of neuron, one deciding whether the snail is hungry, and the other deciding whether there is food in the vicinity. Named Gee Geronimo, this snail was owned by Christopher Hudson of Hove, East Sussex, UK, gastropods that lack a conspicuous shell are commonly called slugs rather than snails. Some species of slug have a red shell, some have only a vestige that serves mainly as a calcium repository. Other than that there is little difference between slugs and snails. There are however important differences in habitats and behavior, slugs squeeze themselves into confined spaces such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground. In such retreats they are in danger from either predators or desiccation. Slugs as a group are far from monophyletic, biologically speaking slug is a term of convenience with little taxonomic significance, the reduction or loss of the shell has evolved many times independently within several very different lineages of gastropods
10.
Clam
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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, however, 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 also 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 also 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 also used for food. Clams can be raw, steamed, boiled, baked or fried. They can also 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 also 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, Kerala, 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
11.
Tusk shell
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Shells of species within this class range from about 0.5 to 15 cm in length. Members of the order Dentaliida tend to be larger than those of the order Gadilida. These molluscs live in soft substrates offshore, molecular data suggest that the scaphopods are a sister group to the cephalopods, although higher-level molluscan phylogeny remains somewhat unresolved. The morphological shape of the body makes it difficult to orient it satisfactorily. As a result, researchers have disagreed as to which direction is anterior/ posterior. According to Shimek and Steiner, he apex of the shell and mantle are anatomically dorsal, consequently, the concave side of the shell and viscera are anatomically dorsal. The convex side has to be divided into ventral and dorsally posterior portions. Functionally, as in cephalopods, the aperture with the foot is anterior, the apical area posterior, the concave side dorsal. The shells of the members of the Gadilida are usually glassy-smooth in addition to being quite narrow and this along with other structures of their anatomy allows them to move with surprising speed through loose sediment to escape potential bottom-dwelling predators. The Dentalids, on the hand, tend to have strongly ribbed. When they sense vibrations anywhere around them, their response is to freeze. This makes them harder to detect by animals such as ratfish which can sense the electrical signals given off by the most minute muscle movement, the mantle of a scaphopod is entirely within the shell. The foot extends from the end of the shell, and is used to burrow through the substrate. The scaphopod positions itself head down in the substrate, with the end of the shell projecting upward. This end seldom appears above the level of the substrate, however, most adult scaphopods live their lives entirely buried within the substrate. Water enters the cavity through the apical aperture, and is wafted along the body surface by cilia. There are no gills, the surface of the mantle cavity absorbs oxygen from the water. Unlike most other molluscs, there is no flow of water with a separate exhalant stream
12.
Caudofoveata
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Caudofoveata is a small class within the phylum Mollusca, also known as Chaetodermomorpha. The class is often combined with Solenogastres and termed Aplacophora, caudofoveata are small, mainly deep sea molluscs. They are worm-like, lacking shells or distinct muscular feet, they instead have scales and calcareous spines called sclerites, caudofoveates live by burrowing through soft sediment, and feed by lying vertically in the sediment with just the mouthparts exposed and taking in passing organic detritus. During sexual reproduction, the female produces eggs which are fertilized and brooded, and then the larvae swim freely
13.
Solenogastres
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The Solenogastres, common name the solenogasters, are one subclass of small, worm-like, shell-less molluscs, the other subclass being the Caudofoveata. Some recent literature, and recent molecular evidence, indicates that the Aplacophora may be polyphyletic, in contrast to all other molluscan classes, the Aplacophora have no shell, and are instead covered by aragonitic sclerites, which can be solid or hollow. These spicules can be arranged perpendicular to one another within the cuticle to form a skeleton, or can stick up to form a palisade, 80% of solenogaster species have a radula, while in others it is secondarily lost. The radula may bear one or more teeth per row, where there is more than one tooth, the radula grows by dividing existing teeth in two, or by adding a new tooth at the centre of the radular row. The salivary glands are very elaborate, and are an important character for taxonomy, next to the mouth they have a unique sense organ, the vestibulum. The solenogastres do not have ctenidia, although their gill-like structures resemble them. During development many Solenogastres are covered by a spiny scleritome comprising spines or scale-like plates, sclerites of Epimenia start out solid before developing a hollow stem that subsequently solidifies. Solenogasters feed on cnidaria and ctenophores, either sucking their bodily fluids or eating their tissue and they do not use their radulae to rasp prey, as other molluscs do. There is some uncertainty regarding the position of the solenogasters. Traditionally considered to be the most basal group and the sister group to the Caudofoveata. Indeed, some molecular datasets plot Solenogastres as an outgroup to Mollusca, mikkelsen N. T. & Lieb B. Fast evolving 18S rRNA sequences from Solenogastres resist standard PCR amplification and give new insights into mollusk substitution rate heterogeneity
14.
Malacology
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Malacology is the branch of invertebrate zoology that deals with the study of the Mollusca, the second-largest phylum of animals in terms of described species after the arthropods. Mollusks include snails and slugs, clams, octopus and squid, one division of malacology, conchology, is devoted to the study of mollusk shells. Malacology derives from Greek μαλακός, malakos, soft, and -λογία, fields within malacological research include taxonomy, ecology and evolution. Applied malacology studies medical, veterinary, and agricultural applications, for example mollusks as vectors of disease, archaeology employs malacology to understand the evolution of the climate, the biota of the area, and the usage of the site. In 1681, Filippo Bonanni wrote the first book published that was solely about seashells. The book was entitled, Ricreatione dell occhio e dela mente nell oservation delle Chiociolle, proposta a curiosi delle opere della natura, in 1868, the German Malacological Society was founded. Zoological methods are used in malacological research, Malacological field methods and laboratory methods were summarized by Sturm et al. Those who study malacology are known as malacologists and those who study primarily or exclusively the shells of mollusks are known as conchologists. The Conchologist -> The Journal of Malacology The Festivus - a peer-reviewed journal which started as a newsletter in 1970. The Nautilus - since 1886 published by Bailey-Matthews Shell Museum, First two volumes were published under name The Conchologists’ Exchange. Impact factor,0.500 The Veliger - impact factor,0, proceedings of the First European Malacological Congress. Text in English with black-and-white photographic reproductions, also maps and diagrams, published by the Conchological Society of Great Britain and Ireland and the Malacological Society of London in 1965 with no ISBN. The long dawn of Malacology, a history of malacology from prehistory to the year 1800. Archives of Natural History 22, 301-319, media related to Malacology at Wikimedia Commons Periodicals about molluscs at WorldCat
15.
Conchology
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Conchology is the study of mollusc shells. Conchology is one aspect of malacology, the study of molluscs, however, malacology is the study of molluscs as whole organisms and it includes the study of land and freshwater mollusc shells as well as seashells and extends to the study of a gastropods operculum. Conchology is now seen as an archaic study, because relying on only one aspect of an organisms morphology can be misleading. However, a shell often gives at least some insight into molluscan taxonomy, even in current museum collections it is common for the dry material to greatly exceed the amount of material that is preserved whole in alcohol. Conchologists mainly deal with four orders, the gastropods, bivalves, Polyplacophora. Cephalopods only have internal shells, with the exception of the Nautiloidea. Some groups, such as the sea slug nudibranchs, have lost their shells altogether, the terms shell collector and conchologist can be regarded as two distinct categories. Not all shell collectors are conchologists, some are concerned with the aesthetic value of shells instead of their scientific study. It is also true that not all conchologists are shell collectors, there is some debate in the conchological community, with some people regarding all shell collectors as conchologists. Molluscs have probably been used by primates as a food long before humans evolved. Shell collecting, the precursor of conchology, probably goes back as far as there have been living near beaches. Stone Age seashell necklaces have been found, sometimes in areas far from the ocean, Shell jewellery is found at almost all archaeological sites, including at ancient Aztec ruins, digs in ancient China, and the Indus Valley. During the Renaissance people began taking interest in objects of beauty to put in cabinets of curiosities. Because of their attractiveness, variety, durability and ubiquity, shells became a part of these collections. Towards the end of the 17th century, people looking at shells with scientific interest. Martin Lister in 1685–1692 published Historia Conchyliorum, which was the first comprehensive conchological text, george Rumpf, or Rumphius, published the first mollusc taxonomy. He suggested single shelled ones, snails or whelks, and two-shelled ones, many of Rumpfs terms were adopted by Carl Linnaeus. Rumpf continued to do important scientific work after he went blind, the study of zoology, including conchology, was revolutionized by Swedish naturalist Carl Linnaeus and his system of binomial nomenclature
16.
Species
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In biology, a species is the basic unit of biological classification and a taxonomic rank. A species is defined as the largest group of organisms in which two individuals can produce fertile offspring, typically by sexual reproduction. While this definition is often adequate, looked at more closely it is problematic, for example, with hybridisation, in a species complex of hundreds of similar microspecies, or in a ring species, the boundaries between closely related species become unclear. Other ways of defining species include similarity of DNA, morphology, all species are given a two-part name, a binomial. The first part of a binomial is the genus to which the species belongs, the second part is called the specific name or the specific epithet. For example, Boa constrictor is one of four species of the Boa genus, Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped that species could evolve given sufficient time, Charles Darwins 1859 book The Origin of Species explained how species could arise by natural selection. Genes can sometimes be exchanged between species by horizontal transfer, and species may become extinct for a variety of reasons. In his biology, Aristotle used the term γένος to mean a kind, such as a bird or fish, a kind was distinguished by its attributes, for instance, a bird has feathers, a beak, wings, a hard-shelled egg, and warm blood. A form was distinguished by being shared by all its members, Aristotle believed all kinds and forms to be distinct and unchanging. His approach remained influential until the Renaissance, when observers in the Early Modern period began to develop systems of organization for living things, they placed each kind of animal or plant into a context. Many of these early delineation schemes would now be considered whimsical, animals likewise that differ specifically preserve their distinct species permanently, one species never springs from the seed of another nor vice versa. In the 18th century, the Swedish scientist Carl Linnaeus classified organisms according to shared physical characteristics and he established the idea of a taxonomic hierarchy of classification based upon observable characteristics and intended to reflect natural relationships. At the time, however, it was widely believed that there was no organic connection between species, no matter how similar they appeared. However, whether or not it was supposed to be fixed, by the 19th century, naturalists understood that species could change form over time, and that the history of the planet provided enough time for major changes. Jean-Baptiste Lamarck, in his 1809 Zoological Philosophy, described the transmutation of species, proposing that a species could change over time, in 1859, Charles Darwin and Alfred Russel Wallace provided a compelling account of evolution and the formation of new species. Darwin argued that it was populations that evolved, not individuals and this required a new definition of species. Darwin concluded that species are what appear to be, ideas
17.
Giant clam
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The giant clam, known as pā’ua in Cook Islands Māori, is a clam that is the largest living bivalve mollusk. Tridacna gigas is one of the most endangered clam species, antonio Pigafetta documented these in his journal as early as 1521. They are also found off the shores of the Philippines, where they are called taklobo, Tridacna gigas lives in flat coral sand or broken coral and can be found at depths of as much as 20 m. Its range covers the Indo-Pacific, but populations are diminishing quickly, Tridacna maxima has the largest geographical distribution among giant clam species, it can be found off high- or low-elevation islands, in lagoons or fringing reefs. Its rapid growth rate is due to its ability to cultivate algae in its body tissue. Although larval clams are planktonic, they become sessile in adulthood, the creatures mantle tissues act as a habitat for the symbiotic single-celled dinoflagellate algae from which the adult clams get most of their nutrition. By day, the clam opens its shell and extends its mantle tissue so that the algae receive the sunlight they need to photosynthesize, young T. gigas are difficult to distinguish from other species of Tridacnidae. Adult T. gigas are the giant clams unable to close their shells completely. Even when closed, part of the mantle is visible, unlike the very similar T. derasa, however, this can only be recognized with increasing age and growth. Small gaps always remain between shells through which retracted brownish-yellow mantle can be seen. Tridacna gigas has four or five vertical folds in its shell, this is the characteristic that separates it from the very similar shell of T. derasa. As with massive deposition of coral matrices composed of calcium carbonate, the mantles edges are packed with symbiotic zooxanthellae that presumably utilize carbon dioxide, phosphates, and nitrates supplied by the clam. The largest known T. gigas specimen measured 137 centimetres and it was discovered around 1817 on the north western coast of Sumatra. The weight of the two shells was 230 kilograms and this suggests that the live weight of the animal would have been roughly 250 kilograms. Today these shells are on display in a museum in Northern Ireland, another unusually large giant clam was found in 1956 off the Japanese island of Ishigaki. However, it was not examined scientifically before 1984, the shells length was 115 centimetres and the weight of the shells and soft parts was 333 kilograms. Scientists estimated the weight to be around 340 kilograms. Algae provide giant clams with a source of nutrition
18.
Mantle (mollusc)
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The mantle is a significant part of the anatomy of molluscs, it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself. In many species of molluscs the epidermis of the mantle secretes calcium carbonate and conchiolin, in sea slugs there is a progressive loss of the shell and the mantle becomes the dorsal surface of the animal. The words mantle and pallium both originally meant cloak or cape, see mantle, the mantle cavity is a central feature of molluscan biology. This cavity is formed by the skirt, a double fold of mantle which encloses a water space. This space contains the gills, anus, osphradium, nephridiopores. The mantle cavity functions as a chamber in most molluscs. In bivalves it is part of the feeding structure. In some molluscs the mantle cavity is a chamber, and in cephalopods and some bivalves such as scallops. In cephalopods the contraction of the mantle is used to water through a tubular siphon, the hyponome. In gastropods it is used as a kind of foot for locomotion over the surface, in Patella the foot includes the entire ventral surface of the animal. The foot of the Bivalvia is a fleshy process adapted by its form to digging rather than to locomotion, in shelled molluscs, the mantle is the organ that forms the shell, and adds to the shell to increase its size and strength as the animal grows. Shell material is secreted by the cells of the mantle tissue. The mantle of many gastropods is usually fully or partially hidden inside the gastropod shell, in species where the shell is small compared to the size of the body, more of the mantle shows. Shell-less slugs have the mantle fully visible, the dorsal surface of the mantle is called the notum, while the ventral surface of the mantle is called the hyponotum. In the family Philomycidae, the covers the whole back side of the body. Mollusc shell, which is formed by the mantle Siphon, which is a part of the mantle in some groups of molluscs
19.
Calcium carbonate
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Calcium carbonate is a chemical compound with the formula CaCO3. It is a substance found in rocks as the minerals calcite and aragonite and is the main component of pearls and the shells of marine organisms, snails. Calcium carbonate is the ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a supplement or as an antacid. Calcium carbonate shares the properties of other carbonates. CaCO3 + CO2 + H2O → Ca2 This reaction is important in the erosion of rock, forming caverns. An unusual form of calcium carbonate is the hexahydrate, ikaite, ikaite is stable only below 6 °C. The vast majority of calcium used in industry is extracted by mining or quarrying. Pure calcium carbonate, can be produced from a quarried source. Alternatively, calcium carbonate is prepared from calcium oxide, other forms can be prepared, the denser, orthorhombic λ-CaCO3 and μ-CaCO3, occurring as the mineral vaterite. The aragonite form can be prepared by precipitation at temperatures above 85 °C, calcite contains calcium atoms coordinated by 6 oxygen atoms, in aragonite they are coordinated by 9 oxygen atoms. The vaterite structure is not fully understood, magnesium carbonate MgCO3 has the calcite structure, whereas strontium and barium carbonate adopt the aragonite structure, reflecting their larger ionic radii. Calcite, aragonite and vaterite are pure calcium carbonate minerals, industrially important source rocks which are predominantly calcium carbonate include limestone, chalk, marble and travertine. Eggshells, snail shells and most seashells are predominantly calcium carbonate, oyster shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source. While not practical as a source, dark green vegetables such as broccoli. Beyond Earth, strong evidence suggests the presence of Calcium carbonate on Mars, signs of Calcium Carbonate have been detected at more than one location. This provides some evidence for the past presence of liquid water, Carbonate is found frequently in geologic settings and constitute an enormous carbon reservoir. Calcium carbonate occurs as aragonite, calcite and dolomite, the carbonate minerals form the rock types, limestone, chalk, marble, travertine, tufa, and others
20.
Periostracum
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The periostracum is a thin organic coating or skin which is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs it is seen in snails and clams, i. e. in gastropods and bivalves. Periostracum is an part of the shell, and it forms as the shell forms. The word periostracum means around the shell, meaning that the periostracum is wrapped around what is usually the more part of the shell. Technically the calcareous part of the shell can be referred to as the ostracum and this shell layer is composed of a type of protein known as conchiolin. Conchiolin is largely composed of quinone-tanned proteins, which are similar to found in the epidermal cuticle. The formation of a shell requires certain biological machinery and this caps of the extrapallial space, which is bounded on its other surfaces by the existing shell and the mantle. The accumulation of ions is driven by ion pumps packed within the calcifying epithelium, the organic matrix forms the scaffold that directs crystallization, and the deposition and rate of crystals is also controlled by hormones produced by the mollusc. The periostracum was probably essential in allowing early molluscs to obtain large size with a single valve, the periostracum is secreted from a groove in the mantle, termed the periostracal groove. When secreted, it consists of the soluble protein periostracin, this polymer becomes insoluble through a process involving quinone. Periostracum is often yellowish or brownish in color, in some species it is black. The periostracum is very often a different color than the layer of the shell. Periostracum can in some cases be quite thin, smooth, glossy and transparent, such that it looks almost like a thin yellow varnish, or it can be thicker, when it is thick it is often relatively rough in texture and dull. In some species the periostracum is tufted, or forms hair-like growths which in some cases can give the shell a velvety feel. In some species the periostracum adheres very tightly to the shell surface. In certain marine species, such as for certain species of cone snails. It is not uncommon for collectors to deliberately remove a periostracum layer if they feel that a shell is more attractive without it. However the periostracum is an important part of the shell, and is definitely of interest to malacologists, details of the periostracum can sometimes be very helpful in identifying a species
21.
Neopilina
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Neopilina is a highly derived genus of modern monoplacophoran. Some molecular results show that they fall within the polyplacophoran clade, fossil and morphological data show that they are rather derived and bear very little resemblance to an ancestral mollusc. Its anatomy led researchers to believe that the cephalopods evolved from the Monoplacophora and its pair of preoral tentacles are considered homologous to those of gastropods, like prosobranch gastropod tentacles, their nerves connect to the cerebral ganglia. The post-oral tentacles are equated with bivalves labial flaps, cephalopods arms, cuticular hardenings around the mouth of the organism are considered to be jaw-like and very not far removed from the beaks of cephalopods or the jaws of many gastropods. It bears a similar degree of similarity to most other mollusc groups, the shell itself is aragonitic, consisting mainly of a prismatic layer, lined with nacre. The organism bears five pairs of ctenidia, unusually for molluscs and this is unlike the polyplacophora, who have a number of pairs of ctenidia, but this number varies and is not related to the number of their body segments. Neopilina is a feeder, probably a deposit feeder, whilst alive
22.
Nautilus (genus)
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Nautilus is a genus of cephalopods in the family Nautilidae. Species in this genus differ significantly in terms of morphology from those placed in the sister taxon Allonautilus, the oldest fossils of the genus are known from the Late Eocene Hoko River Formation, in Washington State and from Late-Eocene to Early Oligocene sediments in Kazakhstan. The oldest fossils of the modern species Nautilus pompilius are from Early Pleistocene sediments off the coast of Luzon in the Philippines, the common term nautilus usually refers to any extant members of the Nautilidae family. Extinct species are denoted with a cross
23.
Decapentaplegic
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Decapentaplegic is a key morphogen involved in the development of the fruit fly Drosophila melanogaster. It is known to be necessary for the patterning of the fifteen imaginal discs. It has also suggested that Dpp plays a role in regulating the growth. Flies with mutations in decapentaplegic fail to form these structures correctly, studies of Dpp in Drosophila have led to greater understanding of the function and importance of their homologs in vertebrates like humans. The most studied tissue in which Dpp is found is the wing, in the wing, Dpp is strongly expressed in a narrow stripe of cells down the middle of the wing where the tissue marks the border between the anterior and posterior sides. Dpp diffuses from this stripe towards the edges of the tissue, Dpp, like its vertebrate homologs, is a signaling molecule. In Drosophila, the receptor for Dpp is formed by two proteins, Thickveins and Punt, like Dpp itself, Tkv and Punt are highly similar to homologs in other species. When a cell receives a Dpp signal, the receptors are able to activate an intracellular protein called mothers against dpp by phosphorylation, the initial discovery of mad in Drosophila paved the way for later experiments that identified the responder to TGF-β signaling in vertebrates, called SMADs. Activated Mad is able to bind to DNA and act as a factor to affect the expression of different genes in response to Dpp signaling. Genes activated by Dpp signaling include optomotor blind and spalt, another gene with a more complicated regulatory interaction with Dpp is brinker. Brinker is a factor that represses the activation targets of Dpp. In the fly wing, the posterior and anterior halves of the tissue are populated by different kinds of cells that express different genes, cells in the posterior but not the anterior express the transcription factor Engrailed. One of the genes activated by En is hedgehog, a signaling factor, hedgehog signaling instructs neighboring cells to express Dpp, but Dpp expression is also repressed by En. The result is that Dpp is only produced in a stripe of cells immediately adjacent to. Dpp produced at this anterior/posterior border then diffuses out to the edges of the tissue, by reading their position along the gradient of Dpp, cells in the wing are able to determine their location relative to the anterior/posterior border, and they behave and develop accordingly. Several experiments have been done to disprove this hypothesis and establish that it is actually the gradient of actual Dpp molecules that are responsible for patterning. Mutant forms of the Dpp receptor Tkv exist that behave as if they are receiving high amounts of Dpp signal even in the absence of Dpp. Cells that contain this mutant receptor behave as if they are in an environment of high Dpp such as the area near the stripe of cells producing Dpp
24.
Hox gene
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Hox genes are a group of related genes that control the body plan of an embryo along the cranio-caudal axis. After the embryonic segments have formed, the Hox proteins determine the type of segment structures that form on a given segment. Hox proteins thus confer segmental identity, but do not form the segments themselves. An analogy for the Hox genes can be made to the role of a director that calls which scene the actors should carry out next. If the play director calls the scenes in the wrong order, similarly, mutations in the Hox genes can result in body parts and limbs in the wrong place along the body. Like a play director, the Hox genes do not act in the play or participate in limb formation themselves, the protein product of each Hox gene is a transcription factor. Each Hox gene contains a well-conserved DNA sequence known as the homeobox, Hox genes are thus a subset of the homeobox transcription factor genes. The products of Hox genes are Hox proteins, the same Hox protein can act as a repressor at one gene and an activator at another. The ability of Hox proteins to bind DNA is conferred by a part of the referred to as the homeodomain. The homeodomain is a 60-amino-acid-long DNA-binding domain and this amino acid sequence folds into a helix-turn-helix motif that is stabilized by a third helix. In addition, homeodomains of individual Hox proteins usually exhibit greater similarity to homeodomains in other species than to proteins encoded by adjacent genes within their own Hox cluster. The functional conservation of Hox proteins can be demonstrated by the fact that a fly can function well with a chicken Hox protein in place of its own. So, despite having a last common ancestor that lived over 670 million years ago, Drosophila melanogaster is an important model for understanding body plan generation and evolution. The general principles of Hox gene function and logic elucidated in flies will apply to all bilaterian organisms, Drosophila, like all insects, has eight Hox genes. These are clustered into two complexes, both of which are located on chromosome 3, the Antennapedia complex consists of five genes, labial, proboscipedia, deformed, sex combs reduced, and Antennapedia. The Bithorax complex, named after the Ultrabithorax gene, consists of the three genes, Ultrabithorax, abdominal-A and abdominal-B. The lab gene is the most anteriorly expressed gene and it is expressed in the head, primarily in the intercalary segment, and also in the midgut. Loss of function of lab results in the failure of the Drosophila embryo to internalize the mouth, failure of head involution disrupts or deletes the salivary glands and pharynx
25.
C-type lectin
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A C-type lectin is a type of carbohydrate-binding protein domain known as a lectin. The C-type designation is from their requirement for calcium for binding, proteins that contain C-type lectin domains have a diverse range of functions including cell-cell adhesion, immune response to pathogens and apoptosis. Drickamer et al. classified C-type lectins into 7 subgroups based on the order of the protein domains in each protein. This classification was updated in 2002, leading to seven additional groups. Most recently, three further subgroups were added
26.
Diatom
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Diatoms are a major group of algae, and are among the most common types of phytoplankton. Diatoms are unicellular, although they can form colonies in the shape of filaments or ribbons, fans, zigzags, the first diatom formally described in scientific literature, the colonial Bacillaria paradoxa, was found in 1783 by Danish naturalist Otto Friedrich Müller. Diatoms are producers within the food chain, a unique feature of diatom cells is that they are enclosed within a cell wall made of silica called a frustule. These frustules show a diversity in form, but are usually almost bilaterally symmetrical. The symmetry is not perfect since one of the valves is slightly larger than the other, fossil evidence suggests that they originated during, or before, the early Jurassic period. Only male gametes of centric diatoms are capable of movement by means of flagella, diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality. More than 200 genera of living diatoms are known, with an estimated 100,000 extant species, diatoms are a widespread group and can be found in the oceans, in fresh water, in soils, and on damp surfaces. They dominate over phytoplankton in nutrient-rich coastal waters and during oceanic spring blooms since they can more rapidly than phytoplankton. Most live pelagically in open water, although some live as surface films at the water-sediment interface and they are especially important in oceans, where they contribute an estimated 45% of the total oceanic primary production of organic material. Spatial distribution of phytoplankton species is restricted both horizontally and vertically. Though most are microscopic, some species of diatoms can reach up to 2 mm in length, diatoms belong to a large group called the heterokonts, including both autotrophs and heterotrophs. Their yellowish-brown chloroplasts are typical of heterokonts, having four membranes, individuals usually lack flagella, but they are present in male gametes of the centric diatoms and have the usual heterokont structure, except they lack the hairs characteristic in other groups. Most diatoms are nonmotile, as their relatively dense cell walls cause them to readily sink, planktonic forms in open water usually rely on turbulent mixing of the upper layers by the wind to keep them suspended in sunlit surface waters. Some species actively regulate their buoyancy with intracellular lipids to counter sinking, a feature of diatoms is the urea cycle, which links them evolutionarily to animals. This was discovered in research carried out by Andrew Allen, Chris Bowler and their study showed that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionally linked in such a way that animals and plants are not. Diatom cells are contained within a unique cell wall known as a frustule made up of two valves called thecae, that typically overlap one another. The biogenic silica composing the wall is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is extruded to the cell exterior and added to the wall
27.
Manchester Museum
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Manchester Museum is a museum displaying works of archaeology, anthropology and natural history and is owned by the University of Manchester. Sited on Oxford Road at the heart of the group of neo-Gothic buildings. It is the UKs largest university museum and serves both as a visitor attraction and as a resource for academic research and teaching. It has around 360,000 visitors each year, the museums first collections were assembled by the Manchester Society of Natural History formed in 1821 with the purchase of the collection of John Leigh Philips. In 1850 the collections of the Manchester Geological Society were added, by the 1860s both societies encountered financial difficulties and, on the advice of the evolutionary biologist Thomas Huxley, Owens College accepted responsibility for the collections in 1867. The museum in Peter Street was sold in 1875 after Owens College moved to new buildings in Oxford Street, the Manchester Museum was opened to the public in 1888. At the time, the departments of the college were immediately adjacent. Two subsequent extensions mirror the development of its collections, the 1912 pavilion was largely funded by Jesse Haworth, a textile merchant, to house the archaeological and Egyptological collections acquired through excavations he had supported. The 1927 extension was built to house the ethnographic collections, the Gothic Revival street frontage which continues to the Whitworth Hall has been ingeniously integrated by three generations of the Waterhouse family. When the adjacent University Dental Hospital of Manchester moved to a new site, its old building was used for teaching, the museum is one of the University of Manchesters cultural assets, along with the Whitworth Art Gallery, John Rylands Library, Jodrell Bank visitor centre and others. In 1997 the museum was awarded £12, the Fossils Gallery and Living Cultures Galleries were developed at this time. The Manchester Gallery explores the relationship between the museum, Manchester and the rest of the world. It explores where collections came from and how they relate to colonialism, Living Worlds opened in April 2011 as a new type of natural history gallery to encourage visitors to reflect on their attitudes to nature. The gallery was designed by Brussels-based design firm villa eugenie, exhibits include a mounted demoiselle crane with a piece of rubble from the Hiroshima atomic bomb blast and hundreds of origami cranes. Themed exhibits explore attitudes to nature and environmental issues, the gallery has a smartphone app, Living Worlds. This gallery has an allotment in the courtyard in front of the museum, Ancient Worlds opened in October 2012 and transformed the main galleries of the 1912 building. Egyptian Worlds, takes visitors on a journey through the landscape, customs, exploring Objects, reveals the archaeology collections through visible storage with a difference. The gallery incorporates a haptic interactive, in June 2013 time-lapse footage showing a 10-inch Egyptian statue in the museums collection, apparently spinning around unaided, attracted worldwide media attention
28.
Indeterminate growth
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In biology and botany, indeterminate growth is growth that is not terminated in contrast to determinate growth that stops once a genetically pre-determined structure has completely formed. Thus, a plant that grows and produces flowers and fruit until killed by frost or some external factor is called indeterminate. In reference to an inflorescence, a type is one in which the first flowers to develop and open are from the buds at the base. The growth of the shoot is not impeded by the opening of the flowers or development of fruits and its appearance is of growing, producing. Not all plants produce indeterminate inflorescences however, some produce a terminal flower that terminates the development of new buds towards the tip of that inflorescence. In most species produce a determinate inflorescence in this way, all of the flower buds are formed before the first ones begin to open. In some species with determinate inflorescences however, the flower blooms first, which stops the elongation of the main axis. One type of example is Dianthus another type is exemplified by Allium, in zoology, indeterminate growth refers to the condition where animals grow rapidly when young, and continue to grow after reaching adulthood although at a slower pace. It is common in fish, amphibians, reptiles, and many molluscs, the term also refers to the pattern of hair growth sometimes seen in humans and a few domestic breeds, where hair continues to grow in length until it is cut. Some mushrooms – notably Cantharellus californicus – also exhibit indeterminate growth
29.
Conchiolin
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Conchiolins are complex proteins which are secreted by a molluscs outer epithelium. These proteins are part of a matrix of organic macromolecules, mainly proteins and polysaccharides and this organic matrix also holds and binds to the crystals of aragonite which give such shells their stiffness. Some land snails have thin, transparent, tan-colored shells, even as adults. Mollusc shell Periostracum Corneous Chitin Tectin Sporopollenin Structure of the cases of the prisms in Mytilus edulis
30.
Gladius (cephalopod)
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The gladius, or pen, is a hard internal bodypart found in many cephalopods of the superorder Decapodiformes and in a single extant member of the Octopodiformes, the vampire squid. It is so named for its resemblance to the Roman short sword of the same name, and is a vestige of the ancestral mollusc shell. The gladius is located dorsally within the mantle and usually extends for its entire length, composed primarily of chitin, it lies within the shell sac, which is responsible for its secretion. Gladii are known from a number of cephalopod groups, including teudopseids, loligosepiids. Gladii are shaped in many ways and vary considerably between species, though are often like a feather or leaf. Cuttlebone Belemnoidea Argonaut Nautilus Mollusc shell Bizikov, V. A, squid gladius, its use for the study of growth, age, intraspecies structure and evolution. Institute of Oceanology, SSSR Academy of Sciences, Moscow, the comparative morphology of the gladius in the order Teuthoidea in relation to systematics and phylogeny. University of Miami, Coral Gables, Florida, smithsonian Contributions to Zoology 586, 55–67
31.
Epitonium scalare
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Epitonium scalare, common name the precious wentletrap, is a predatory or ectoparasitic species of marine gastropod with an operculum, in the family Epitoniidae, the wentletraps. In the 17th and 18th century this was considered to be a very rare shell. Johan de la Faille and Cosimo III de Medici owned a wentletrap and this species is distributed in the Red Sea, in the Indian Ocean along Madagascar and South Africa, in the South West Pacific Ocean and along Fiji Islands and Japan. Adult shells of this species attain a length of between 25 mm to 72 mm, many Epitonium species have shells that are very attractive and quite interesting in their structure. Dance, S. Peter,1969, Rare Shells, University of California Press.128 p,24 color plates, ISBN9780571082179 Gastropods. com, Epitonium scalare scalare, accessed,22 November 2010
32.
Quinone
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The class includes some heterocyclic compounds. The prototypical member of the class is 1, 4-benzoquinone or cyclohexadienedione, other important examples are 1, 2-benzoquinone,1, 4-naphthoquinone and 9, 10-anthraquinone. Quinones are electrophilic Michael acceptors stabilised by conjugation, depending on the quinone and the site of reduction, reduction can either rearomatise the compound or break the conjugation. Conjugate addition nearly always breaks the conjugation, the term quinone is also used more generally for a large class of compounds formally derived from aromatic quinones through replacement of some hydrogen atoms by other atoms or radicals. A large scale application of quinones is for the production of hydrogen peroxide. Derivatives of quinones are common in biologically active molecules, some serve as electron acceptors in electron transport chains such as those in photosynthesis, and aerobic respiration. Phylloquinone is also known as Vitamin K1 as it is used by animals to help form certain proteins, which are involved in coagulation, bone formation. Natural or synthetic quinones show a biological or pharmacological activity, and they embody some claims in herbal medicine. These applications include purgative, antimicrobial and antiparasitic, anti-tumor, inhibition of PGE2 biosynthesis, many natural and artificial coloring substances are quinone derivatives. They are second only to azo dyes in importance as dyestuffs, alizarin, extracted from the madder plant, was the first natural dye to be synthesized from coal tar. Benzoquinone is used in chemistry as an oxidizing agent. Strongly oxidizing quinones include chloranil and 2, 3-dichloro-5, 6-dicyano-1,9, 10-Anthraquinone-2, 7-disulphonic acid a quinone similar to one found naturally in rhubarb has been used as a charge carrier in metal-free flow batteries. Quinones are commonly named with a prefix indicates the parent aromatic hydrocarbon. Infix multipliers -di-, -tri-, -tetra- are used there are 4,6,8 carbonyls. The position of the groups can be indicated before the prefix or after it. Anthraquinone Benzoquinone Naphthoquinone Plastoquinone Pyrroloquinoline quinone Quinones at the US National Library of Medicine Medical Subject Headings
33.
Protein
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Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, a linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide, short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid residues are bonded together by peptide bonds, the sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the code specifies 20 standard amino acids, however. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors, proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes. Once formed, proteins only exist for a period of time and are then degraded and recycled by the cells machinery through the process of protein turnover. A proteins lifespan is measured in terms of its half-life and covers a wide range and they can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal and or misfolded proteins are degraded more rapidly due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms, many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized, digestion breaks the proteins down for use in the metabolism. Methods commonly used to study structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance. Most proteins consist of linear polymers built from series of up to 20 different L-α-amino acids, all proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from this structure as it contains an unusual ring to the N-end amine group. The amino acids in a chain are linked by peptide bonds. Once linked in the chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen. The peptide bond has two forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar
34.
Seashell
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A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer created by an animal that lives in the sea. The shell is part of the body of the animal, empty seashells are often found washed up on beaches by beachcombers. The shells are empty because the animal has died and the parts have been eaten by another animal or have rotted out. The term seashell usually refers to the exoskeleton of an invertebrate, most shells that are found on beaches are the shells of marine mollusks, partly because many of these shells endure better than other seashells. Apart from mollusk shells, other shells that can be found on beaches are those of barnacles, horseshoe crabs, marine annelid worms in the family Serpulidae create shells which are tubes made of calcium carbonate that are cemented onto other surfaces. The shells of sea urchins are called tests, and the shells of crabs. While most seashells are external, some cephalopods have internal shells, Seashells have been used by humans for many different purposes throughout history and pre-history. However, seashells are not the kind of shells, in various habitats, there are shells from freshwater animals such as freshwater mussels and freshwater snails. When the word refers only to the shells of marine mollusks. The study of the entire molluscan animal is known as malacology, Seashells are commonly found in beach drift, which is natural detritus deposited along strandlines on beaches by the waves and the tides. Shells are very often washed up onto an empty and clean. Empty seashells are often picked up by beachcombers, however, the majority of seashells which are offered for sale commercially have been collected alive and then killed and cleaned, specifically for the commercial trade. This type of large-scale exploitation can sometimes have a negative impact on local ecosystems. The word seashell is often used to only the shell of a marine mollusk. These shells are often the most commonly encountered, both in the wild, and for sale as decorative objects. Marine species of gastropods and bivalves are more numerous land and freshwater species. The shells of species also often have more sculpture and more color. Although there are a number of species of shelled mollusks that are large, there are vast numbers of extremely small species too
35.
Pyrrole
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Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e. g. N-methylpyrrole, porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as heme. Pyrroles are components of more complex macrocycles, including the porphyrins of heme, the chlorins, bacteriochlorins, chlorophyll, Pyrrole is a colorless volatile liquid that darkens readily upon exposure to air, and is usually purified by distillation immediately before use. Pyrrole is a 5-membered aromatic heterocycle, like furan and thiophene, unlike furan and thiophene, it has a dipole in which the positive end lies on the side of the heteroatom, with a dipole moment of 1.58 D. In CDCl3, it has chemical shifts at 6.68 and 6.22, Pyrrole is weakly basic, with a conjugate acid pKa of −3.8. The most thermodynamically stable pyrrolium cation is formed by protonation at the 2 position, Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid pKa of +3.7. Pyrrole is also weakly acidic at the N–H position, with a pKa of 17.5, Pyrrole was first detected by F. F. Runge in 1834, as a constituent of coal tar. In 1857, it was isolated from the pyrolysate of bone and its name comes from the Greek pyrrhos, from the reaction used to detect it—the red color that it imparts to wood when moistened with hydrochloric acid. Pyrrole itself is not naturally occurring, but many of its derivatives are found in a variety of cofactors, other pyrrole-containing secondary metabolites include PQQ, makaluvamine M, ryanodine, rhazinilam, lamellarin, prodigiosin, myrmicarin, and sceptrin. The syntheses of pyrrole-containing haemin, synthesized by Emil Fischer was recognized by the Nobel Prize, Pyrrole is a constituent of tobacco smoke and not as an ingredient. Pyrrole is prepared industrially by treatment of furan with ammonia in the presence of acid catalysts, like SiO2. Pyrrole can also be formed by dehydrogenation of pyrrolidine. Several syntheses of the ring have been described. The Hantzsch pyrrole synthesis is the reaction of β-ketoesters with ammonia, the Knorr pyrrole synthesis involves the reaction of an α-amino ketone or an α-amino-β-ketoester with an activated methylene compound. The method involves the reaction of an α-aminoketone and a compound containing a methylene group α to a carbonyl group, in the Paal–Knorr pyrrole synthesis, a 1, 4-dicarbonyl compound reacts with ammonia or a primary amine to form a substituted pyrrole. The Van Leusen reaction can be used to form pyrroles, by reaction of tosylmethyl isocyanide with an enone in the presence of base, a 5-endo cyclization then forms the 5-membered ring, which reacts to eliminate the tosyl group. The last step is tautomerization to the pyrrole, the Barton–Zard synthesis proceeds in a manner similar to the Van Leusen synthesis
36.
Porphyrin
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Porphyrins are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges. The parent porphyrin is porphin, and substituted porphines are called porphyrins, the porphyrin ring structure is aromatic, with a total of 26 electrons in the conjugated system. Various analyses indicate that not all atoms of the ring are involved equally in the conjugation or that the overall nature is substantially based on several smaller conjugated systems. Many porphyrins are naturally occurring, one of the best-known porphyrins is heme, the pigment in red blood cells, porphyrins are the conjugate acids of ligands that bind metals to form complexes. The metal ion usually has a charge of 2+ or 3+. A schematic equation for these syntheses is shown, H2porphyrin + 2+ → MLn−4 +4 L +2 H+ where M = metal ion, some iron-containing porphyrins are called hemes. Heme-containing proteins, or hemoproteins, are found extensively in nature, hemoglobin and myoglobin are two O2-binding proteins that contain iron porphyrins. Several other heterocycles are related to porphyrins and these include corrins, chlorins, bacteriochlorophylls, and corphins. Chlorins are more reduced, contain more hydrogen than porphyrins, and this structure occurs in a chlorophyll molecule. Replacement of two of the four subunits with pyrrolinic subunits results in either a bacteriochlorin or an isobacteriochlorin. Some porphyrin derivatives follow Hückels rule, but most do not, a benzoporphyrin is a porphyrin with a benzene ring fused to one of the pyrrole units. E. g. verteporfin is a benzoporphyrin derivative, a geoporphyrin, also known as a petroporphyrin, is a porphyrin of geologic origin. They can occur in oil, oil shale, coal. Abelsonite is possibly the only geoporphyrin mineral, as it is rare for porphyrins to occur in isolation, in plants, algae, bacteria and archaea, it is produced from glutamic acid via glutamyl-tRNA and glutamate-1-semialdehyde. The enzymes involved in this pathway are glutamyl-tRNA synthetase, glutamyl-tRNA reductase and this pathway is known as the C5 or Beale pathway. Two molecules of dALA are then combined by porphobilinogen synthase to give porphobilinogen, four PBGs are then combined through deamination into hydroxymethyl bilane, which is hydrolysed to form the circular tetrapyrrole uroporphyrinogen III. This molecule undergoes a number of further modifications, intermediates are used in different species to form particular substances, but, in humans, the main end-product protoporphyrin IX is combined with iron to form heme. Bile pigments are the products of heme
37.
Calcite
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Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of hardness, based on scratch hardness comparison. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite, aragonite will change to calcite at 380–470 °C, and vaterite is even less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime and it is thus etymologically related to chalk. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals, however, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms and it may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form and its fracture is conchoidal, but difficult to obtain. It has a defining Mohs hardness of 3, a gravity of 2.71. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes, acute scalenohedral crystals are sometimes referred to as dogtooth spar while the rhombohedral form is sometimes referred to as nailhead spar. Single calcite crystals display an optical property called birefringence and this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669, at a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in water, acidity can cause dissolution of calcite. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite, calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, high-grade optical calcite was used in World War II for gun sights, specifically in bomb sights and anti-aircraft weaponry
38.
Aragonite
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Aragonite is a carbonate mineral, one of the two most common, naturally occurring, crystal forms of calcium carbonate, CaCO3. It is formed by biological and physical processes, including precipitation from marine, aragonites crystal lattice differs from that of calcite, resulting in a different crystal shape, an orthorhombic crystal system with acicular crystal. Repeated twinning results in pseudo-hexagonal forms, Aragonite may be columnar or fibrous, occasionally in branching stalactitic forms called flos-ferri from their association with the ores at the Carinthian iron mines. The type location for aragonite is Molina de Aragón,25 km from Aragon for which it was named in 1797, an aragonite cave, the Ochtinská Aragonite Cave, is situated in Slovakia. In the US, aragonite in the form of stalactites and cave flowers is known from Carlsbad Caverns, massive deposits of oolitic aragonite sand are found on the seabed in the Bahamas. Aragonite is the high pressure polymorph of calcium carbonate, as such, it occurs in high pressure metamorphic rocks such as those formed at subduction zones. Aragonite forms naturally in almost all mollusk shells, and as the calcareous endoskeleton of warm-, because the mineral deposition in mollusk shells is strongly biologically controlled, some crystal forms are distinctively different from those of inorganic aragonite. In some mollusks, the shell is aragonite, in others. The nacreous layer of the fossil shells of some extinct ammonites forms an iridescent material called ammolite. Aragonite also forms in the ocean and in caves as inorganic precipitates called marine cements and speleothems, Aragonite is not uncommon in serpentinites where high Mg in pore solutions apparently inhibits calcite growth and promotes aragonite precipitation. Aragonite is metastable at the low pressures near the Earths surface and is commonly replaced by calcite in fossils. Aragonite older than the Carboniferous is essentially unknown and it can also be synthesized by adding a calcium chloride solution to a sodium carbonate solution at temperatures above 60 °C or in water-ethanol mixtures at ambient temperatures. Aragonite is thermodynamically unstable at temperature and pressure, and tends to alter to calcite on scales of 107 to 108 years. The mineral vaterite, also known as μ-CaCO3, is another phase of calcium carbonate that is metastable at ambient conditions typical of Earths surface, in aquaria, aragonite is considered essential for the replication of reef conditions. Aragonite provides the necessary for much sea life and also keeps the pH of the water close to its natural level. Aragonite has been tested for the removal of pollutants like zinc, cobalt. Aragonite sea Ikaite, CaCO3·6H2O Monohydrocalcite, CaCO3·H2O Nacre, otherwise known as Mother-of-Pearl Oolitic aragonite sand The Ochtinska aragonite cave Kosovo Caves Aragonite Formations
39.
Nacre
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Nacre, also known as mother of pearl, is an organic-inorganic composite material produced by some molluscs as an inner shell layer, it also makes up the outer coating of pearls. It is strong, resilient, and iridescent, nacre is found in some of the most ancient lineages of bivalves, gastropods, and cephalopods. The outer layer of pearls and the layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Other mollusc families that have an inner shell layer include marine gastropods such as the Haliotidae, the Trochidae. Nacre is composed of hexagonal platelets of aragonite 10–20 µm wide and 0.5 µm thick arranged in a continuous parallel lamina and these layers are separated by sheets of organic matrix composed of elastic biopolymers. This mixture of brittle platelets and the layers of elastic biopolymers makes the material strong and resilient. Strength and resilience are also likely to be due to adhesion by the arrangement of the platelets. This structure, at multiple length sizes, greatly increases its toughness, nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light. These structures interfere constructively and destructively with different wavelengths of light at different viewing angles, the crystallographic c-axis points approximately perpendicular to the shell wall, but the direction of the other axes varies between groups. Adjacent tablets have shown to have dramatically different c-axis orientation. In bivalves and cephalopods, the points in the direction of shell growth. The interlocking of bricks of nacre has large impact on both the mechanism as well as its toughness. In addition, the mineral–organic interface results in enhanced resilience and strength of the organic interlayers, nacre formation is not fully understood. The initial onset assembly, as observed in Pinna nobilis, is driven by the aggregation of nanoparticles within a matrix that arrange in fibre-like polycrystalline configurations. The particle number increases successively and, when critical packing is reached, nacre growth is mediated by organics, controlling the onset, duration and form of crystal growth. Individual aragonite bricks are believed to grow to the full height of the nacreous layer. This produces the hexagonal close-packing characteristic of nacre, bricks may nucleate on randomly dispersed elements within the organic layer, well-defined arrangements of proteins, or may grow epitaxially from mineral bridges extending from the underlying tablet. Nacre differs from fibrous aragonite – a brittle mineral of the same form – in that the growth in the c-axis is slow in nacre, nacre is secreted by the epithelial cells of the mantle tissue of various molluscs
40.
Opisthobranchia
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Euopisthobranchia is a revised collection of opisthobranchs that is monophyletic, but this group leaves out some traditional opisthobranchs including the Sacoglossa and the Acochlidiacea. The subclass Heterobranchia now contains the species used to be assigned to Opisthobranchia plus the Pulmonata. The Opisthobranchia included species in the order Cephalaspidea, the sacoglossans, anaspidean sea hares, pelagic sea angels, sea butterflies, opisthobranch means gills behind of the heart. In contrast, Prosobranch means gills in front, opisthobranchs are characterized by two pairs of tentacles and a single gill behind and to the right of the heart. Opisthobranchia are known from as early as the Carboniferous, under the old classification system by Johannes Thiele in 1931, class Gastropoda was divided into three subclasses, Prosobranchia, Pulmonata and Opisthobranchia. The latter two were combined into a single order. They are now included within the subclass Heterobranchia, although many manuals, a phylogenetic study published in November 2004, gave new definitions of the seven main lineages of the Opisthobranchia. Accordingly, articles no longer use the term Opisthobranchia, replacing it with Heterobranchia to emphasise a different concept, by 2011, the Opisthobranchia were declared artificial and obsolete and were replaced by new phylogenetic hypotheses. As a result of this detorsion, the visceral ganglia no longer overlap and are described as euthyneurous, there is no marked distinction between head and mantle. The tentacles, situated close to the mouth, are used for orientation, behind them are the rhinophores, olfactory organs which often have complex forms. The middle part of the foot is the sole, used for locomotion, the sides of the foot have evolved into parapodia, fleshy winglike outgrowths. In several suborders, such as the Thecosomata and Gymnosomata, these parapodia are used to move in a swimming motion and their eyes are simple pit-cup eyes with a lens and cornea capable of detecting light and the passage of shadows but not of producing a coherent image. Opisthobranchia represents a diverse group of gastropods occupying a great variety of ecological niches. Opisthobranchs have a distribution, but are restricted almost exclusively to marine habitats with the only exception being few freshwater acochlidians. Principally soft-bodied marine creatures with a reduced or absent shell and no operculum, due to a combination of outstanding camouflage and aggressive toxicity they have few predators. Animals that do predate opisthobranchs include other opisthobranchs and toxin-resistant predators like sea spiders, opisthobranchs secrete irritants such as strong acids or accumulate toxins from their food. Aeolidioidea pirate the stinging cells from their prey and use them for their own defense. Opisthobranchs may be herbivores, detritivores or carnivores, being slow, the carnivores hunt sedentary prey
41.
Pulmonata
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Pulmonata, or pulmonates, is an informal group of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includes many land and freshwater families, and several marine families, the taxon Pulmonata as traditionally defined was found to be polyphyletic in a molecular study per Jörger et al. dating from 2010. Pulmonata are known from the Carboniferous Period to the present, pulmonates have a single atrium and kidney, and a concentrated, symmetrical, nervous system. The mantle cavity is located on the side of the body. Most species have a shell, but no operculum, although the group also include several shell-less slugs. Pulmonates are hermaphroditic, and some groups possess love darts, & A. E. Gray,1806 Superfamily Strophocheiloidea Thiele,1926 Superfamily Trigonochlamydoidea Hese,1882 Superfamily Zonitoidea Mörch,1864. Superfamily Athoracophoroidea P. Fischer,1883 = Tracheopulmonata and they proposed the more inclusive taxon Panpulmonata to unite the clades Siphonarioidea, Sacoglossa, Glacidorboidea, Pyramidelloidea, Amphiboloidea, Hygrophila, Acochlidia and Eupulmonata. Wade, C. M. Mordan, P. B, a phylogeny of the land snails. Proceedings of the Royal Society B, Biological Sciences, holznagel, W. E. Colgan, D. J. Lydeard, C. Pulmonate phylogeny based on 28S rRNA gene sequences, A framework for discussing habitat transitions, pulmonate snails & slugs in captivity
42.
Semi-slug
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Semi-slugs, also spelled semislugs, are land gastropods whose shells are too small for them to retract into, but not quite vestigial. The shell of some semi-slugs may not be visible on casual inspection. This is a type of gastropod that is intermediate between a slug and a land snail, there exist a number of gastropod families that have semi-slugs species. There exist about 1000 species of semi-slugs in comparison to about only 500 species of slugs
43.
Slug
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Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word slug is often used as part of the common name of any gastropod mollusc that has no shell. Various taxonomic families of land slugs form part of quite different evolutionary lineages. Thus, the families of slugs are not closely related. The shell-less condition has arisen many times independently during the evolutionary past, of the six orders of Pulmonata, two – the Onchidiacea and Soleolifera – solely comprise slugs. A third family, the Sigmurethra, contains various clades of snails, the taxonomy of this group is in the process of being revised in light of DNA sequencing. It appears that pulmonates are paraphyletic and basal to the opisthobranchs, the family Ellobiidae are also polyphyletic. E. The upper pair is light sensing and has eyespots at the ends, mantle On top of the slug, behind the head, is the saddle-shaped mantle, and under this are the genital opening and anus. On one side of the mantle is an opening, which is easy to see when open. This opening is known as the pneumostome, tail The part of a slug behind the mantle is called the tail. Keel Some species of slugs, for example Tandonia budapestensis, have a prominent ridge running over their back along the middle of the tail and this ridge is called a keel. Foot The bottom side of a slug, which is flat, is called the foot, like almost all gastropods, a slug moves by rhythmic waves of muscular contraction on the underside of its foot. It simultaneously secretes a layer of mucus that it travels on, around the edge of the foot in some taxa is a structure called the foot fringe. Vestigial shell Most slugs retain a remnant of their shell, which is usually internalized and this organ generally serves as storage for calcium salts, often in conjunction with the digestive glands. An internal shell is present in the Limacidae and Parmacellidae, adult Philomycidae, Onchidiidae and Veronicellidae lack shells. Slugs bodies are made up mostly of water and, without a full-sized shell and they must generate protective mucus to survive. Many species are most active just after rain because of the moist ground, in drier conditions, they hide in damp places such as under tree bark, fallen logs, rocks and man-made structures, such as planters, to help retain body moisture. Like all other gastropods, they undergo torsion during development, Slugs produce two types of mucus, one is thin and watery, and the other thick and sticky
44.
Pearl
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A pearl is a hard object produced within the soft tissue of a living shelled mollusk or another animal, such as a conulariid. Just like the shell of a clam, a pearl is composed of calcium carbonate. in minute crystalline form, the ideal pearl is perfectly round and smooth, but many other shapes, known as baroque pearls, can occur. The finest quality natural pearls have been valued as gemstones. Because of this, pearl has become a metaphor for something rare, fine, the most valuable pearls occur spontaneously in the wild, but are extremely rare. These wild pearls are referred to as natural pearls, cultured or farmed pearls from pearl oysters and freshwater mussels make up the majority of those currently sold. Imitation pearls are widely sold in inexpensive jewelry, but the quality of their iridescence is usually very poor and is easily distinguished from that of genuine pearls. Pearls have been harvested and cultivated primarily for use in jewelry and they have also been crushed and used in cosmetics, medicines and paint formulations. Whether wild or cultured, gem-quality pearls are almost always nacreous and iridescent, however, almost all species of shelled mollusks are capable of producing pearls of lesser shine or less spherical shape. The English word pearl comes from the French perle, originally from the Latin perna meaning leg, nacreous pearls, the best-known and most commercially significant, are primarily produced by two groups of molluskan bivalves or clams. A nacreous pearl is made from layers of nacre, by the same living process as is used in the secretion of the mother of pearl which lines the shell, natural pearls, formed without human intervention, are very rare. Cultured pearls are formed in pearl farms, using human intervention as well as natural processes, saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae. Freshwater pearls grow within certain species of mussels in the order Unionida. The unique luster of pearls depends upon the reflection, refraction, the thinner and more numerous the layers in the pearl, the finer the luster. The iridescence that pearls display is caused by the overlapping of successive layers, in addition, pearls can be dyed yellow, green, blue, brown, pink, purple, or black. The very best pearls have a metallic mirror-like luster, because pearls are made primarily of calcium carbonate, they can be dissolved in vinegar. Calcium carbonate is susceptible to even a weak acid solution because the crystals of calcium carbonate react with the acid in the vinegar to form calcium acetate. Freshwater and saltwater pearls may sometimes look quite similar, but they come from different sources, Freshwater pearls form in various species of freshwater mussels, family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh water. These freshwater pearl mussels occur not only in hotter climates, most freshwater cultured pearls sold today come from China
45.
Trochidae
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The Trochidae, common name top-snails or top-shells, are a taxonomic family of very small to large sea snails, marine gastropod molluscs in the clade Vetigastropoda. This family is known as the top-snails because in many species the shell resembles a toy spinning top. The animal is similar in form to the Turbinidae. The top snails are characterized by primitive traits, a heart with two atria. They have retained only one kidney and the second osphradium has been lost in the course of evolution, the mantle cavity contains a single gill. Along the side of the foot are three or more pairs of sensory epipodial tentacles, the head has a short, broad rostrum. The intertentacular lobes are simple or digitated, separate or united across the front, the jaws are developed or absent. The rhachidian teeth are present and well-developed. The lateral teeth generally number 5 on each side, sometimes more numerous, the marginal teeth are narrow and very numerous. The length of a shell varies between 5 mm and 130 mm. There is also a variation in the shape of the shell. This goes from low auriform with an aperture to the long. The shape may also be subglobose, turbinate or helicoid and their height may vary between 3 mm and 152 mm. The shell contains only a few whorls and these have a highly variable exterior, ranging from smooth or glossy to sculptured. They have a brown, entirely corneous, circular, multispiral operculum which fits the aperture snugly, the operculum is formed of numerous gradually increasing whorls with a central nucleus. The aperture may be entire, tetragonal or rounded and has no reflected lip, the peristome is generally not continuous. These shells are brightly colored and adorned with darker bands. The Trochidae differ from the Turbinidae in having a corneous, never calcareous, operculum, most species in the family live either in the intertidal zone or in the shallow subtidal zone, but some live in deeper water
. PMID 16675549.
