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Mollusca
Fossil range: Cambrian–Recent
Tonicella lineata, a polyplacophoran or chiton, antecedent end arise the right
Scientific classification
Kingdom: Animalia
Superphylum: Lophotrochozoa
Phylum: Mollusca
Linnaeus, 1758
Classes

Aplacophora
Bivalvia
Caudofoveata
Cephalopoda
Gastropoda
† Helcionelloida
Monoplacophora
Polyplacophora
† Rostroconchia
Scaphopoda
Diversity
85,0001 accustomed active species

The Mollusca, common name molluscs or mollusks,note 1 is a ample phylum of invertebrate animals. There are about 85,000 accustomed extant species of molluscs. This is the better marine phylum, absolute about 23% of all the alleged abyssal organisms. Numerous molluscs aswell reside in freshwater and earthbound habitats. Molluscs are awful diverse, not abandoned in admeasurement and in anatomical structure, but aswell in behaviour and in habitat.

Contents

Taxonomy

The phylum Mollusca is about disconnected into nine or ten taxonomic classes, of which two are extinct. The gastropods (snails and slugs) cover by far the a lot of classified species, accounting for 80% of the total. Cephalopod molluscs such as squid, cuttlefish and octopus are a allotment of the a lot of neurologically advanced invertebrates. Either the giant squid or the colossal squid is the better accustomed species of beastly after a backbone.

Opinions alter about the bulk of classes of molluscs—for archetype the table beneath shows eight active classes,2 and two abolished ones. About some authors amalgamate the Caudofoveata and solenogasters into one class, the Aplacophora.34 Two of the frequently accustomed classes are accustomed abandoned from fossils5

Class Major organisms Described active species2 Distribution
Caudofoveata4 worm-like organisms 120 seabed 200–3,000 metres (660–9,800 ft)
Aplacophora4 solenogasters, worm-like organisms 200 seabed 200–3,000 metres (660–9,800 ft)
Polyplacophora6 chitons 1,000 rocky flat breadth and seabed
Monoplacophora7 limpet-like organisms 31 seabed 1,800–7,000 metres (5,900–23,000 ft); one breed 200 metres (660 ft)
Gastropoda8 abalone, limpets, conch, nudibranchs, sea hares, sea butterfly, snails, slugs 70,000 marine, freshwater, land
Cephalopoda9 squid, octopus, cuttlefish, nautilus 900 marine
Bivalvia10 clams, oysters, scallops, geoducks, mussels 20,000 marine, freshwater
Scaphopoda11 tusk shells 500 marine 6–7,000 metres (20–23,000 ft)
Rostroconchia †12 fossils; apparent ancestors of bivalves extinct marine
Helcionelloida †13 fossils; backward bacilli such as Latouchella extinct marine

Distinguishing features

The two a lot of accustomed actualization of the physique anatomy of molluscs are a mantle with a cogent atrium acclimated for breathing and excretion, and the alignment of the afraid system. Because of the abounding ambit of anatomical diversity, abounding textbooks abject their descriptions on a academic "generalized mollusc", with actualization accustomed to abounding but not all classes aural the Mollusca.

Diversity

About 80% of all accustomed mollusc breed are gastropods (snails and slugs), including the cowry (a sea snail) pictured here.5

Estimates of accustomed declared active breed of molluscs alter from 50,000 to a best of 120,000 species.1 In 2009 Chapman estimated the bulk of declared active breed at 85,000.1 Haszprunar in 2001 estimated about 93,000 named species,2 which cover 23% of all alleged abyssal organisms.14 Molluscs are added abandoned to arthropods in numbers of active beastly species5—far abaft the arthropods' 1,113,000 but able-bodied avant-garde of chordates' 52,000.15 It has been estimated that there are about 200,000 active breed in total,161 and 70,000 deposit species,17 although the absolute bulk of mollusc breed that anytime existed, whether or not preserved, accept to be abounding times greater than the bulk animate today.18

Molluscs accept added assorted forms than any added beastly phylum. They cover snails, slugs and added gastropods; clams and added bivalves; squids and added cephalopods; and added lesser-known but analogously appropriate sub-groups. The majority of breed still reside in the oceans, from the seashores to the abyssal zone, but some anatomy a significant allotment of the freshwater fauna and the earthbound ecosystems. Molluscs are acutely assorted in tropical and temperate regions but can be begin at all latitudes.19 About 80% of all accustomed mollusc breed are gastropods.5 Cephalopoda such as squid, cuttlefish and octopus are a allotment of the neurologically a lot of avant-garde of all invertebrates.20 The giant squid, which until afresh had not been empiric animate in its developed form,21 is one of the better invertebrates. About a afresh bent case of the colossal squid, 10 metres (33 ft) continued and acceptance 500 kilograms (0.49 LT; 0.55 ST), may accept overtaken it.22

Freshwater and earthbound molluscs arise awfully accessible to extinction. Estimates of the numbers of non-marine molluscs alter widely, partly because abounding regions accept not been thoroughly surveyed. There is aswell a curtailment of specialists who can analyze all the animals in any one breadth to species. However, in 2004 the IUCN Red List of Threatened Breed included about 2,000 endangered non-marine molluscs. For comparison, the abounding majority of molluscs breed are abyssal but abandoned 41 of these appeared on the 2004 Red List. 42% of recorded extinctions back the year 1500 are of molluscs, about absolutely non-marine species.23

Definition

The words mollusc and mollusk are both acquired from the French mollusque, which originated from the Latin molluscus, from mollis, soft. Molluscus was itself an adjustment of Aristotle's τᾲ μαλάκια, "the bendable things", which he activated to cuttlefish.24 The scientific abstraction of molluscs is accustomed as malacology.25

Molluscs accept developed such a assorted ambit of physique structures that it is difficult to acquisition synapomorphies (defining characteristics) that administer to all avant-garde groups.19 The a lot of accepted appropriate of molluscs is that they are unsegmented and bilaterally symmetrical.26 The afterward are present in all avant-garde molluscs:2717

Other characteristics that frequently arise in textbooks accept cogent exceptions:

  Class
Characteristic17 Aplacophora4 Polyplacophora6 Monoplacophora7 Gastropoda28 Cephalopoda29 Bivalvia30 Scaphopoda11
Radula, a abrasion "tongue" with chitinous teeth Absent in 20% of Neomeniomorpha Yes Yes Yes Yes No Internal, cannot extend aloft body
Broad, able-bodied foot Reduced or absent Yes Yes Yes Modified into arms Yes Small, abandoned at "front" end
Dorsal absorption of centralized organs (visceral mass) Not obvious Yes Yes Yes Yes Yes Yes
Large digestive ceca No ceca in some aplacophora Yes Yes Yes Yes Yes No
Large circuitous metanephridia ("kidneys") None Yes Yes Yes Yes Yes Small, simple

A "generalized mollusc"

Further information: Mollusc shell
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    Digestive & excretory system
    Circulatory & respiratory
    Central afraid system
    Changeable system
 1 Radula
 2 Mouth
 3 Shell
 4 Stomach
 5 Gonad
 6 Heart
 7 Coelom
 9 Mantle
10 Crimson cavity
11 Anus
12 Gill
13 Foot
15 Pedal nerve cord
16 Gut
17 Belly nerve cord
18 Assumption ring
A ambiguous mollusc31

Because of the astronomic variations amid groups of molluscs, abounding altercation books alpha the accountable by anecdotic a "generalized mollusc", which some advance may resemble actual aboriginal molluscs and which is rather agnate to avant-garde monoplacophorans.192773

The ambiguous mollusc has a single, "limpet-like" shell on top. The carapace is buried by a crimson that covers the high surface. The base consists of a abandoned able-bodied "foot".27. The belly mass, or visceropallium, is the soft, non-muscular metabolic arena of the mollusc. It contains the physique organs.26

Mantle and crimson cavity

The crimson atrium is a bend in the crimson that encloses a cogent bulk of space. It is lined with epidermis. It is exposed, according to habitat, to sea, beginning baptize or air. The atrium was at the rear in the ancient molluscs but its position now varies from accumulation to group. The anus, a brace of osphradia (chemical sensors) in the admission "lane", the afterwards brace of gills and the avenue openings of the nephridia ("kidneys") and gonads (reproductive organs) are in the crimson cavity.27. The accomplished bendable physique of bivalves lies aural an continued crimson cavity26.

Shell

Main article: Mollusc shell

The crimson bend secretes a carapace (secondarily absent in a bulk of taxonomic groups, such as the nudibranchs26) that consists of mainly chitin and conchiolin (a protein) accustomed with calcium carbonate),2732 except that the exoteric bandage in about all cases is all conchiolin (see periostracum).27 Molluscs never use phosphate to assemble their harder parts,33 with the ambiguous barring of Cobcrephora.34 While a lot of mollusc shells are composed mainly of aragonite, those gastropods that lay eggs with a harder carapace use calcite (sometimes with traces of aragonite) to assemble the eggshells.35

The carapace consists of three layers : the alien bandage (the periostracum) fabricated of amoebic matter, a average bandage fabricated of columnar calcite and an close bandage consisting of laminated calcite, that is about nacreous.26

Foot

The base consists of a able-bodied foot, which has acclimatized to altered purposes in altered classes.36:4 The basal carries a brace of statocysts, which act as antithesis sensors. In gastropods, it secretes mucus as a adipose to aid movement. In forms that accept abandoned a top shell, such as limpets, the basal acts as a accoutrement adhering the beastly to a harder surface, and the vertical anatomy bolt the carapace down over it; in added molluscs, the vertical anatomy cull the basal and added apparent bendable locations into the shell.27 In bivalves, the basal is acclimatized for burrowing into the sediment;36:4 in cephalopods it is acclimated for jet propulsion,36:4 and the tentacles and accoutrements are acquired from the foot.37

Multiple functions of organs

Molluscs organs are acclimated for assorted functions. For example: the affection and nephridia ("kidneys") are important locations of the changeable arrangement as able-bodied as the circulatory and excretory systems; in bivalves, the gills both "breathe" and aftermath a baptize accepted in the crimson cavity, which serves both elimination and reproduction.

Circulation

Molluscs' circulatory systems are mainly open. Although molluscs are coelomates, their coeloms are bargain to adequately baby spaces anchor the affection and gonads. The capital physique atrium is a hemocoel through which claret and coelomic aqueous broadcast and which encloses a lot of of the added centralized organs. These hemocoelic spaces act as an able hydrostatic skeleton26. The claret contains the respiratory pigment hemocyanin as an oxygen-carrier. The affection consists of one or added pairs of atria (auricles), which accept oxygenated claret from the aspect and pump it to the ventricle, which pumps it into the aorta (main artery), which is adequately abbreviate and opens into the hemocoel.27

The atria of the affection aswell action as allotment of the excretory system by clarification decay articles out of the claret and auctioning it into the coleom as urine. A brace of nephridia ("little kidneys") to the rear of and affiliated to the coelom extracts any re-usable abstracts from the urine and depression added decay articles into it, and again ejects it via tubes that acquittal into the crimson cavity.27

Respiration

Most molluscs accept abandoned one brace of gills, or even abandoned one gill. About the aspect are rather like accoutrement in shape, although some breed accept aspect with filaments on abandoned one side. They bisect the crimson atrium so that baptize enters abreast the basal and exits abreast the top. Their filaments accept three kinds of cilia, one of which drives the baptize accepted through the crimson cavity, while the added two advice to accrue the aspect clean. If the osphradia ascertain baneful chemicals or possibly sediment entering the crimson cavity, the gills' cilia may stop assault until the blackballed intrusions accept ceased. Anniversary gill has an admission claret barge affiliated to the hemocoel and an approachable one to the heart.27

Eating, digestion, and elimination

    = Food
    = Radula
    = Odontophore "belt"
    = Muscles
Snail radula at work.

Most molluscs accept able-bodied mouths with radulae, "tongues" address abounding rows of chitinous teeth, which are replaced from the rear as they abrasion out. The radula primarily functions to scrape bacteria and algae off rocks. This radula is associated with the odontophore, a cartilaginous acknowledging organ26

Molluscs mouths aswell accommodate glands that bury clammy mucus, to which the aliment sticks. Assault cilia (tiny "hairs") drive the fungus arise the stomach, so that the fungus forms a continued string.27

At the cone-shaped rear end of the abdomen and bulging hardly into the hindgut is the prostyle, a backward-pointing cone of feces and mucus, which is rotated by added cilia so that it acts as a bobbin, ambagious the fungus cord assimilate itself. Afore the fungus cord alcove the prostyle, the acidity of the abdomen makes the fungus beneath adhesive and frees particles from it.27

The particles are sorted by yet accession accumulation of cilia, which forward the abate particles, mainly minerals, to the prostyle so that eventually they are excreted, while the beyond ones, mainly food, are beatific to the stomach's cecum (a accessory with no added exit) to be digested. The allocation action is by no agency perfect.27

Periodically, annular anatomy at the hindgut's access compression off and defecate a section of the prostyle, preventing the prostyle from growing too large. The anus is in the allotment of the crimson atrium that is swept by the approachable "lane" of the accepted created by the gills. Cannibal molluscs usually accept simpler digestive systems.27

As the arch has abundantly abolished in bivalves, their aperture has been able with labial palps (two on anniversary ancillary of the mouth) to aggregate the detritus from its mucus.26

Nervous system

Molluscs accept two pairs of capital nerve cords (three in bivalves) the visceral cords confined the centralized organs and the pedal ones confined the foot. Both pairs run beneath the akin of the gut, and cover ganglia as bounded ascendancy centers in important locations of the body. A lot of pairs of agnate ganglia on both abandon of the physique are affiliated by commissures (relatively ample bundles of nerves). The abandoned ganglia aloft the gut are the bookish ganglia, which sit aloft the esophagus (gullet) and handle "messages" from and to the eyes. The pedal ganglia, which ascendancy the foot, are just beneath the esophagus and their commissure and access to the bookish ganglia bandage the esophagus in a assumption ring.27

The brain, in breed that accept one, encircles the esophagus. A lot of molluscs accept a arch with eyes, and all accept a brace of sensor-containing tentacles, aswell on the head, that ascertain chemicals, accordance and touch.27

Reproduction

Apical bunch (cilia)
Prototroch (cilia)
Stomach
Mouth
Metatroch (cilia)
Mesoderm
Anus
/// = cilia
Trochophore larva38

The simplest molluscan changeable arrangement relies on external fertilization, but there are added circuitous variations. All aftermath eggs, from which may arise trochophore larvae, added circuitous veliger larvae, or miniature adults. Two gonads sit next to the coelom, a baby atrium that surrounds the affection and allow ova or sperm into the coloem, from which the nephridia abstract them and allow them into the crimson cavity. Molluscs that use such a arrangement abide of one sex all their lives and await on external fertilization. Some molluscs use internal fertilization and/or are hermaphrodites, activity as both sexes; both of these methods crave added circuitous changeable systems.27

The a lot of basal molluscan larva is a trochophore, which is planktonic and feeds on amphibian aliment particles by application the two bands of cilia annular its "equator" to ambit aliment into the mouth, which uses added cilia to drive them into the stomach, which uses added cilia to belch undigested charcoal through the anus. New tissue grows in the bands of mesoderm in the interior, so that the aciculate bunch and anus are pushed added afar as the beastly grows. The trochophore date is about succeeded by a veliger date in which the prototroch, the "equatorial" bandage of cilia abutting the aciculate tuft, develops into the velum ("veil"), a brace of cilia-bearing lobes with which the larva swims. Eventually the larva sinks to the seafloor and metamorphoses into the developed form. Whilst alteration is the accepted accompaniment in molluscs, the cephalopods alter in announcement absolute development: the hatchling is a 'miniaturized' anatomy of the adult.39

Evolution

Fossil record

There is acceptable affirmation for the actualization of gastropods, cephalopods and bivalves in the Cambrian aeon 542 to 488.3 actor years ago. However, the evolutionary history both of the actualization of molluscs from the affiliated accumulation Lophotrochozoa, and of their about-face into the acclaimed active and fossil forms, is still agilely debated.

There is agitation about whether some Ediacaran and Aboriginal Cambrian fossils absolutely are molluscs. Kimberella, from about 555 actor years ago, has been declared as "mollusc-like",4041 but others are afraid to go added than "probable bilaterian".4243 There is an even bluff agitation about whether Wiwaxia, from about 505 actor years ago, was a mollusc, and abounding of this centers on whether its agriculture accoutrement was a blazon of radula or added agnate to that of some polychaete worms.4244 Nicholas Butterfield, who opposes the abstraction that Wiwaxia was a mollusc, has accounting that beforehand microfossils from 515 to 510 actor years ago are bits of a absolutely mollusc-like radula.45

The tiny Helcionellid deposit Yochelcionella is anticipation to be an aboriginal mollusc13
Spirally coiled shells arise in abounding gastropods28

However, the Helcionellids, which aboriginal arise over 540 actor years ago in Aboriginal Cambrian rocks from Siberia and China,4647 are anticipation to be aboriginal molluscs with rather backward shells. Shelled molluscs accordingly predate the ancient trilobites.13 Although a lot of helcionellid fossils are abandoned a few millimeters long, specimens a few centimeters continued accept aswell been found, a lot of with added limpet-like shapes. There accept been suggestions that the tiny specimens were juveniles and the beyond ones adults.48

Some analyses of helcionellids assured that these were the ancient gastropods.49 About added scientists are not assertive that Aboriginal Cambrian fossils appearance bright signs of the torsion that identifies avant-garde gastropods twists the centralized organs so that the anus lies aloft the head.285051

    = Septa
    = Siphuncle
Septa and siphuncle in nautiloid shell

For a continued time it was anticipation that Volborthella, some fossils of which pre-date 530 actor years ago, was a cephalopod. About discoveries of added abounding fossils showed that Volborthella’s carapace was not buried but congenital from grains of the mineral silicon dioxide (silica), and that it was not disconnected into a alternation of compartments by septa as those of deposit shelled cephalopods and the active Nautilus are. Volborthella’s allocation is uncertain.52 The Late Cambrian deposit Plectronoceras is now anticipation to be the ancient acutely cephalopod fossil, as its carapace had septa and a siphuncle, a fiber of tissue that Nautilus uses to abolish baptize from compartments that it has abandoned as it grows, and which is aswell arresting in deposit ammonite shells. However, Plectronoceras and added aboriginal cephalopods crept forth the seafloor instead of swimming, as their shells independent a "ballast" of adamant deposits on what is anticipation to be the base and had stripes and blotches on what is anticipation to be the high surface.53 All cephalopods with alien shells except the nautiloids became abolished by the end of the Cretaceous aeon 65 actor years ago.54 However, the shell-less Coleoidea (squid, octopus, cuttlefish) are abounding today.55

The Aboriginal Cambrian fossils Fordilla and Pojetaia are admired as bivalves.56575859 "Modern-looking" bivalves appeared in the Ordovician period, 488 to 443 actor years ago.60 One bivalve group, the rudists, became above reef-builders in the Cretaceous, but became abolished in the Cretaceous-Tertiary extinction.61 Even so, bivalves abide abounding and diverse.

The Hyolitha is a chic of abolished animals with a carapace and operculum that may be molluscs. Authors who advance that they deserve their own phylum do not animadversion on the position of this phylum in the timberline of life62

Phylogeny

Lophotrochozoa

Brachiopods






Bivalves


Monoplacophorans
("limpet-like", "living fossils")



Gastropods
(snails, slugs, limpets, sea hares)



Cephalopods
(nautiloids, ammonites, squid, etc.)


Scaphopods (tusk shells)







Aplacophorans
(spicule-covered, worm-like)


Polyplacophorans (chitons)




Halwaxiids

Wiwaxia


Halkieria



Orthrozanclus



Odontogriphus



A accessible "family tree" of molluscs (2007).6364 Does not cover annelid worms as the assay concentrated on fossilizable "hard" features.63

The phylogeny (evolutionary "family tree") of molluscs is a arguable subject. In accession to the debates about whether Kimberella and any of the "halwaxiids" were molluscs or carefully accompanying to molluscs,41424445 there are debates about the relationships amid the classes of active molluscs.43 In actuality some groups frequently classifed as molluscs may accept to be redefined as audible but related.65

Molluscs are about admired associates of the Lophotrochozoa,63 a accumulation authentic by accepting trochophore larvae and, in the case of active Lophophorata, a agriculture anatomy alleged a lophophore. The added associates of the Lophotrochozoa are the annelid worms and seven abyssal phyla.66 The diagram on the appropriate summarizes a phylogeny presented in 2007.

Because the relationships amid the associates of the ancestors timberline are uncertain, it difficult to analyze the actualization affiliated from the endure accustomed antecedent of all molluscs.67 For example, it is ambiguous whether the affiliated mollusc was metameric (composed of repeating units)—if it was, that would advance an agent from an annelid-like worm.68 Scientists disagree about this: Giribet and colleagues assured in 2006 that the alliteration of aspect and of the foot's retractor anatomy were after developments, 19 while in 2007 Sigwart assured that the affiliated mollusc was metameric, and that it had a basal acclimated for bit-by-bit and a "shell" that was mineralized.43 In one accurate one annex of the ancestors tree, the carapace of conchiferans is anticipation to accept acquired from the spicules (small spines) of aplacophorans; about this is difficult to accommodate with the embryological origins of spicules.67

The molluscan carapace appears to accept originated from a fungus coating, which eventually stiffened into a cuticle. This would accept been closed and appropriately affected the development of added adult respiratory accoutrement in the anatomy of gills.13 Eventually, the cuticle would accept become mineralized,13 application the aforementioned abiogenetic accouterment (engrailed) as a lot of added bilaterian skeletons.68 The aboriginal mollusc carapace about absolutely was able with the mineral aragonite.69

The evolutionary relationships within the molluscs are aswell debated, and the diagrams beneath appearance two broadly accurate reconstructions:

However, an assay in 2009 that acclimated both morphological and molecular phylogenetics comparisons assured that the molluscs are not monophyletic; in particular, that Scaphopoda and Bivalvia are both separate, monophyletic lineages different to the actual molluscan classes—in added words that the acceptable phylum Mollusca is polyphyletic, and that it can abandoned be fabricated monophyletic if scaphopods and bivalves are excluded.65 A 2010 assay analogously assured that the molluscs are not monophyletic, this time suggesting that solenogastres are added carefully accompanying to the non-molluscan taxa acclimated as an outgroup than to added molluscs.70

Human interaction

Molluscs accept for abounding centuries been the antecedent of important affluence goods, conspicuously pearls, mother of pearl, Tyrian purple dye, and sea silk. Their shells accept aswell been acclimated as money in some pre-industrial societies.

There is a accident of aliment contagion from toxins that accrue in molluscs beneath assertive conditions, and abounding countries accept regulations that aim to abbreviate this risk. Blue-ringed octopus bites are about fatal, and the chaw of Octopus rubescens can could could cause necrosis that lasts best than one ages if untreated, and headaches and weakness constant for up to a anniversary even if treated.71 Stings from a few breed of ample close cone shells can aswell kill. However, the adult venoms of these cone snails accept become important accoutrement in neurological assay and appearance affiance as sources of new medications.

Schistosomiasis (also accustomed as bilharzia, bilharziosis or snail fever) is transmitted to bodies via baptize snail hosts, and affects about 200 million people. A few breed of snails and slugs are austere agronomical pests, and in addition, adventitious or advised addition of assorted snail breed into new area has resulted in austere accident to some accustomed ecosystems.

Uses by humans

Further information: Seashell
Mollusc achievement in 2005

Molluscs, abnormally bivalves such as clams and mussels, accept been an important aliment antecedent back at atomic the appearance of anatomically avant-garde humans—and this has about resulted in over-fishing.72 Added frequently eaten molluscs cover octopuses and squids, whelks, oysters, and scallops.73 In 2005, China accounted for 80% of the all-around mollusc catch, applique about 11,000,000 tonnes (11,000,000 LT; 12,000,000 ST). Aural Europe, France remained the industry leader.74 Some countries adapt access and administration of molluscs and added seafood, mainly to abbreviate the adulteration accident from toxins that accrue in the animals.75

Photo of three annular metal cages in shallows, with docks, boathouses and approach copse in background
Saltwater pearl oyster acreage in Seram, Indonesia

Most molluscs that accept shells can aftermath pearls, but abandoned the chaplet of bivalves and some gastropods whose shells are lined with nacre are valuable.2830 The best accustomed chaplet are produced by pearl oyster.s Pinctada margaritifera and Pinctada mertensi, which reside in the tropical and sub-tropical amnion of the Pacific Ocean. Accustomed chaplet anatomy if a baby adopted article gets ashore amid the mantle and shell.

There are two methods of culturing pearls, by inserting either "seeds" or chaplet into oysters. The "seed" adjustment uses grains of arena carapace from freshwater mussels, and over-harvesting for this purpose has endangered several freshwater mollusk breed in the southeastern USA.30 The fair industry is so important in some areas that cogent sums of money are spent on ecology the bloom of farmed molluscs.76

Mosaic of mustachioed, curly-haired man cutting acme and amidst by halo
Byzantine Emperor Justinian I clad in Tyrian purple

Other affluence and high-status articles were fabricated from molluscs. Tyrian purple, fabricated from the ink glands of murex shells, "... fetched its weight in silver" in the fourth-century BC, according to Theopompus.77 The assay of ample numbers of Murex shells on Crete suggests that the Minoans may accept pioneered the abstraction of "Imperial purple" during the Average Minoan aeon in the 20th–18th aeon BC, centuries afore the Tyrians.7879 Sea silk is a fine, attenuate and admired fabric produced from the continued cottony accoutrement (byssus) buried by several bivalve molluscs, decidedly Pinna nobilis, to attach themselves to the sea bed.80 Procopius, autograph on the Persian wars about 550 CE, "stated that the 5 ancestral satraps (governors) of Armenia who accustomed their badge from the Roman Emperor were accustomed chlamys (or cloaks) fabricated from lana pinna (Pinna "wool," or byssus). Apparently abandoned the cardinal classes were accustomed to abrasion these chlamys."81

Mollusc shells, including those of cowries, were acclimated as a affectionate of money in several pre-industrial societies. About these "currencies" about differed in important means from the connected government-backed and -controlled money accustomed to automated societies. Some carapace "currencies" were not acclimated for bartering affairs but mainly as social status displays at important occasions such as weddings.82 If acclimated for bartering affairs they functioned as commodity money, in added words as a tradable article whose amount differed from abode to place, about as a aftereffect of difficulties in transport, and which was accessible to cureless inflation if added able carriage or "goldrush" behavior appeared.83

Stings and bites

The blue-ringed octopus's rings are a admonishing signal—this octopus is alarmed, and its chaw can kill.84

When handled alive, a few breed of molluscs can chaw or chaw and, with some species, this can present a austere accident to the beastly administration the animal. To put this into angle however, deaths from mollusc venoms are beneath than 10% of the bulk of deaths from jellyfish stings.85

All octopuses are venomous86 but abandoned a few breed affectation a cogent blackmail to humans. Blue-ringed octopuses in the brand Hapalochlaena, which reside about Australia and New Guinea, chaw bodies abandoned if acutely provoked,84 but their acidity kills 25% of beastly victims. Accession close species, Octopus apollyon, causes astringent inflammation that can endure for over a ages even if advised correctly.87

Photo of cone on ocean bottom
Live cone snails can be alarming to shell-collectors but are advantageous to neurology researchers88

All breed of cone snails are antagonistic and can chaw if handled, although abounding breed are too baby to affectation abounding of a accident to humans. These are cannibal gastropods that augment on abyssal invertebrates (and in the case of beyond breed on fish). Their acidity is based on a huge arrangement of toxins, some fast-acting and others slower but deadlier—they can allow to do this because their toxins crave beneath time and activity to be produced compared with those of snakes or spiders.88 Abounding aching stings accept been reported, and a few fatalities, although some of the appear fatalities may be exaggerations.85 Abandoned the few beyond breed of cone snail that can abduction and annihilate angle are acceptable to be actively alarming to humans.89 The furnishings of abandoned cone carapace toxins on victims' afraid systems are so absolute that they are advantageous accoutrement for assay in neurology, and the baby admeasurement of their molecules makes it simple to amalgamate them.8890

The acceptable acceptance that a giant clam can allurement the leg of a being amid its valves, appropriately drowning them, is a myth.91

Pests

Skin vesicles created by the assimilation of Schistosoma. Source: Centers for Ache Ascendancy and Prevention

Schistosomiasis (also accustomed as bilharzia, bilharziosis or snail fever) is "second abandoned to malaria as the a lot of adverse abject ache in close countries. An estimated 200 actor bodies in 74 countries are adulterated with the ache — 100 actor in Africa alone."92 The bacteria has 13 accustomed species, of which two affect humans. The bacteria itself is not a mollusc, but all the breed accept freshwater snails as intermediate hosts.93

Some breed of molluscs, decidedly assertive snails and slugs, can be austere crop pests,94 and if alien into new environments can bewilder bounded ecosystems. One such pest, the behemothic African snail Achatina fulica, has been alien to abounding locations of Asia, as able-bodied as to abounding islands in the Indian Ocean and Pacific Ocean. In the 1990s this breed accomplished the West Indies. Attempts to ascendancy it by introducing the bloodthirsty snail Euglandina rosea accepted disastrous, as the predator abandoned Achatina fulica and went on to abate several built-in snail breed instead.95

Despite its name, Molluscum contagiosum is a viral disease, and is different to molluscs.96

Notes

Footnotes

  1. ^ Spelled mollusks in the USA, see affidavit accustomed in Rosenberg's [1]; for the spelling mollusc see the affidavit accustomed by Brusca & Brusca. Invertebrates (2nd ed.). 

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Further reading

  • Starr & Taggart (2002). Biology: The Unity and Assortment of Life. Pacific Grove, California: Thomson Learning. 
  • Nunn, J.D., Smith, S.M., Picton, B.E. and McGrath, D. 2002. Checklist, album of administration and bibliography for the abyssal mollusca of Ireland. in. Abyssal Biodiversity in Ireland and Adjacent Waters. Ulster Museum. advertisement no. 8.
  • Ostroumov, S.A. (2001) An amphiphilic actuality inhibits the mollusk accommodation to clarify out phytoplankton beef from water.—Biology Bulletin, Vol. 28 (1): 95–102. doi: 10.1023/A:1026671024000. PMID: 11236572; http://www.springerlink.com/content/l665628020163255/;
  • The allusive roles of suspension-feeders in ecosystems / Ed. R. Dame, S.Olenin. Dordrecht: Springer. 2005. 360 p.

External links

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Wikispecies has advice accompanying to: Mollusca
The Wikibook Dichotomous Key has a page on the affair of
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Extant phyla of commonwealth Animalia by subkingdom
Parazoa
Mesozoa
Eumetazoa
Basal/disputed
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