Oysters, clams, and mussels, esp. [69] One bivalve group, the rudists, became major reef-builders in the Cretaceous, but became extinct in the Cretaceous–Paleogene extinction event. [26][14](p291–292) Two of the commonly recognized "classes" are known only from fossils.[16]. n. (Animals) any invertebrate of the phylum Mollusca, having a soft unsegmented body and often a shell, secreted by a fold of skin (the mantle). The tiny specimens have been suggested to be juveniles and the larger ones adults. [11] The most general characteristic of molluscs is they are unsegmented and bilaterally symmetrical. Their population status or structure, physiology, behaviour or the level of contamination with elements or compounds can indicate the state of contamination status of the ecosystem. noun An invertebrate of a large phylum which includes snails, slugs, mussels, and octopuses. pl.) [44] Although most helcionellid fossils are only a few millimeters long, specimens a few centimeters long have also been found, most with more limpet-like shapes. The People’s Choice 2020 Word Of The Year: 2020 Was A $#@#%%$@! While most mollusc shells are composed mainly of aragonite, those gastropods that lay eggs with a hard shell use calcite (sometimes with traces of aragonite) to construct the eggshells. 2, McClure's Magazine, Vol 31, No 2, June 1908. [15] The whole soft body of bivalves lies within an enlarged mantle cavity. [36], Cephalopods are primarily predatory, and the radula takes a secondary role to the jaws and tentacles in food acquisition. Synonyms (a weak-willed person): little girl, nose of wax, pushover; Translations Most molluscs have muscular mouths with radulae, "tongues", bearing many rows of chitinous teeth, which are replaced from the rear as they wear out. Glory-of-the-sea snail (Conus gloriamaris) is prized by collectors for its ornate shell. Attempts to control it by introducing the predatory snail Euglandina rosea proved disastrous, as the predator ignored Achatina fulica and went on to extirpate several native snail species, instead. Their venom is a complex mixture of toxins, some fast-acting and others slower but deadlier. Mollusca (n.) "division of invertebrate animals with soft, unsegmented bodies, no jointed legs, and commonly covered by hard shells," 1797, from Modern Latin mollusca, chosen by Linnaeus as the name of an invertebrate order (1758), from neuter plural of Latin molluscus "thin-shelled," from mollis "soft," from PIE root *mel-(1) "soft." [49][52] Nicholas Butterfield, who opposes the idea that Wiwaxia was a mollusc, has written that earlier microfossils from 515 to 510 million years ago are fragments of a genuinely mollusc-like radula. In forms having only a top shell, such as limpets, the foot acts as a sucker attaching the animal to a hard surface, and the vertical muscles clamp the shell down over it; in other molluscs, the vertical muscles pull the foot and other exposed soft parts into the shell. Or do you just have an interest in foreign languages? To employ this strategy, the plant has to be large enough for the mollusc to 'sit' on, so smaller macroscopic plants are not as often eaten as their larger counterparts. Troncoso, J.S., Trigo, J.E. Mollusk definition, any invertebrate of the phylum Mollusca, typically having a calcareous shell of one, two, or more pieces that wholly or partly enclose the soft, unsegmented body, including the chitons, snails, bivalves, squids, and octopuses. Most mollusks have a hard shell that protects the body. Nearly all produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults. a comic character, usually masked, dressed in … ), Aplacophorans(spicule-covered, worm-like), The phylogeny (evolutionary "family tree") of molluscs is a controversial subject. Modified entries © 2019 by Penguin Random House … The trochophore stage is often succeeded by a veliger stage in which the prototroch, the "equatorial" band of cilia nearest the apical tuft, develops into the velum ("veil"), a pair of cilia-bearing lobes with which the larva swims. [11] About 80% of all known mollusc species are gastropods. The Bivalvia would comprise about 14% of the total and the other five classes less than 2% of the living molluscs. [12] The blood of these molluscs contains the respiratory pigment hemocyanin as an oxygen-carrier. Most molluscs have eyes, and all have sensors to detect chemicals, vibrations, and touch. [70] Even so, bivalves remain abundant and diverse. [77] Scientists disagree about this: Giribet and colleagues concluded, in 2006, the repetition of gills and of the foot's retractor muscles were later developments,[11] while in 2007, Sigwart concluded the ancestral mollusc was metameric, and it had a foot used for creeping and a "shell" that was mineralized. One of the grand divisions of the animal kingdom, including the classes Cephalopoda, Gastropoda, PteropodaScaphopoda, and Lamellibranchiata, or Conchifera. Estimates of the numbers of nonmarine molluscs vary widely, partly because many regions have not been thoroughly surveyed. Good evidence exists for the appearance of gastropods (e.g., Aldanella), cephalopods (e.g., Plectronoceras, ?Nectocaris) and bivalves (Pojetaia, Fordilla) towards the middle of the Cambrian period, c. 500 million years ago, though arguably each of these may belong only to the stem lineage of their respective classes. Vertebra, articulata, mollusca, and radiata are evolved by mortal and material thought. Learn more. The large group of animals called mollusks live on land and in both freshwater and salt water. Their filaments have three kinds of cilia, one of which drives the water current through the mantle cavity, while the other two help to keep the gills clean. Schistosomiasis (also known as bilharzia, bilharziosis, or snail fever) is transmitted to humans by water snail hosts, and affects about 200 million people. [84] In 2005, China accounted for 80% of the global mollusc catch, netting almost 11,000,000 tonnes (11,000,000 long tons; 12,000,000 short tons). The phylum is typically divided into 8 or 9 taxonomic classes, of which two are entirely extinct. [76], The molluscan shell appears to have originated from a mucus coating, which eventually stiffened into a cuticle. Within Europe, France remained the industry leader. These hemocoelic spaces act as an efficient hydrostatic skeleton. Many mollusks live…. ; Díaz Agras, G.J. [33], Most molluscs' circulatory systems are mainly open. In gastropods, it secretes mucus as a lubricant to aid movement. [62] All cephalopods with external shells except the nautiloids became extinct by the end of the Cretaceous period 65 million years ago. Start studying Definitions for Mollusca. The "seed" method uses grains of ground shell from freshwater mussels, and overharvesting for this purpose has endangered several freshwater mussel species in the southeastern United States. [85] Some countries regulate importation and handling of molluscs and other seafood, mainly to minimize the poison risk from toxins that can sometimes accumulate in the animals.[86]. [93] When used for commercial transactions, they functioned as commodity money, as a tradable commodity whose value differed from place to place, often as a result of difficulties in transport, and which was vulnerable to incurable inflation if more efficient transport or "goldrush" behavior appeared.[94]. The most universal features of the body structure of molluscs are a mantle with a significant cavity used for breathing and excretion, and the organization of the nervous system. 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 (except for bivalves), and the structure of the nervous system. [36], Most molluscs are herbivorous, grazing on algae or filter feeders. [15] Molluscs never use phosphate to construct their hard parts,[28] with the questionable exception of Cobcrephora. Snails are intermediate hosts for many parasitic flukes. [37] 31 (3–4): 144..), Opinions vary about the number of classes of molluscs; for example, the table below shows seven living classes,[18] and two extinct ones. Along with the insects and vertebrates, it is one of the most diverse groups in the animal kingdom, with nearly 100,000 (possibly [51], There is an even sharper debate about whether Wiwaxia, from about 505 million years ago, was a mollusc, and much of this centers on whether its feeding apparatus was a type of radula or more similar to that of some polychaete worms. Fig. The parasite itself is not a mollusc, but all the species have freshwater snails as intermediate hosts. [45] Additionally, it suggests a sister taxon relationship exists between the Bivalvia and the Gastropoda. Online biomonitoring of bivalve activity, 24/7: This page was last edited on 11 January 2021, at 22:13. Stings from a few species of large tropical cone shells can also kill, but their sophisticated, though easily produced, venoms have become important tools in neurological research. It is a major group in the animal kingdom as regards the number which occu­pies next to arthropods. New tissue grows in the bands of mesoderm in the interior, so the apical tuft and anus are pushed further apart as the animal grows. Members of the mollusc family use intracellular digestion to function. 3.51 A). Others feed on macroscopic 'plants' such as kelp, rasping the plant surface with its radula. mollusc (plural molluscs) A soft-bodied invertebrate of the phylum Mollusca, typically with a hard shell of one or more pieces. ", "Phylogenomics reveals deep molluscan relationships", "New data on Kimberella, the Vendian mollusc-like organism (White Sea region, Russia): palaeoecological and evolutionary implications", "Deep molluscan phylogeny: synthesis of palaeontological and neontological data", 10.1666/0022-3360(2002)076<0287:LECSSF>2.0.CO;2, "Shell microstructures in Early Cambrian molluscs", "A Broad Brush History of the Cephalopoda", 10.1666/0022-3360(2001)075<1119:BSDTC>2.0.CO;2, "Phylogenetic analysis of 73 060 taxa corroborates major eukaryotic groups", "The cell lineage of the polyplacophoran, Chaetopleura apiculata: variation in the spiralian program and implications for molluscan evolution", "Investigation of molluscan phylogeny on the basis of 18S rRNA sequences", "Phylogenetic support values are not necessarily informative: the case of the Serialia hypothesis (a mollusk phylogeny)", "A molecular palaeobiological hypothesis for the origin of aplacophoran molluscs and their derivation from chiton-like ancestors", "China catches almost 11 m tonnes of molluscs in 2005", "Importing fishery products or bivalve molluscs", 10.2983/0730-8000(2006)25[233:DOPOAO]2.0.CO;2, "Doctor snail—Lethal to fish and sometimes even humans, cone snail venom contains a pharmacopoeia of precision drugs", "Cone Shell Mollusc Poisoning, with Report of a Fatal Case", "Venomous mollusks: The risks of human accidents by conus snails (gastropoda: Conidae) in Brazil", "The Carter Center Schistosomiasis Control Program", Researchers complete mollusk evolutionary tree; 26 October 2011, Hardy's Internet Guide to Marine Gastropods, Archaeal Richmond Mine acidophilic nanoorganisms, https://en.wikipedia.org/w/index.php?title=Mollusca&oldid=999774990, Articles containing Ancient Greek (to 1453)-language text, Wikipedia articles incorporating a citation from the 1911 Encyclopaedia Britannica with Wikisource reference, Articles with dead external links from July 2020, Articles with permanently dead external links, CS1 maint: bot: original URL status unknown, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License, Snails, yes; slugs, mostly yes (internal vestigial), Octopuses, no; cuttlefish, nautilus, squid, yes, ancient lineage of molluscs with cap-like shells, seabed 1,800–7,000 metres (5,900–23,000 ft); one species 200 metres (660 ft). Rev. The underside of the animal consists of a single muscular "foot". if inadequately cooked, may transmit the hepatitis A virus or bacterial pathogens. [15], At the tapered rear end of the stomach and projecting slightly into the hindgut is the prostyle, a backward-pointing cone of feces and mucus, which is rotated by further cilia so it acts as a bobbin, winding the mucus string onto itself. A phylum of the kingdom MetazoaMollusca have soft, unsegmented bodies with an anterior head, a dorsal visceral mass, and a ventral foot. There is also a shortage of specialists who can identify all the animals in any one area to species. [107], "Mollusk" redirects here. If the osphradia detect noxious chemicals or possibly sediment entering the mantle cavity, the gills' cilia may stop beating until the unwelcome intrusions have ceased. : a large phylum of invertebrate animals (as snails, clams, and mussels) that have a soft unsegmented body lacking segmented … [12], The mantle cavity, a fold in the mantle, encloses a significant amount of space. The marine … [10], Molluscs have developed such a varied range of body structures, finding synapomorphies (defining characteristics) to apply to all modern groups is difficult. Classification into higher taxa for these groups has been and remains problematic. [1] Haszprunar in 2001 estimated about 93,000 named species,[18] which include 23% of all named marine organisms. [8], The name Molluscoida was formerly used to denote a division of the animal kingdom containing the brachiopods, bryozoans, and tunicates, the members of the three groups having been supposed to somewhat resemble the molluscs. Molluscs that use such a system remain of one sex all their lives and rely on external fertilization. "[104] The parasite has 13 known species, two of which infect humans. The majority of species still live in the oceans, from the seashores to the abyssal zone, but some form a significant part of the freshwater fauna and the terrestrial ecosystems. Molluscs' mouths also contain glands that secrete slimy mucus, to which the food sticks. [3] The number of fossil species is estimated between 60,000 and 100,000 additional species. “Capital” vs. “Capitol”: Do You Know Where You’re Going? Mollusca (prop. The nephridia extract the gametes from the coelom and emit them into the mantle cavity. Molluscs (or mollusks) are an important phylum of invertebrate animals. Research has demonstrated that environmental stress can affect the feeding of bivalves by altering the energy budget of organisms. [24], Freshwater and terrestrial molluscs appear exceptionally vulnerable to extinction. [71], Monoplacophorans("limpet-like", "living fossils"), Gastropods(snails, slugs, limpets, sea hares), Cephalopods(nautiloids, ammonites, octopus, squid, etc. The generalized mollusc has two paired nerve cords, or three in bivalves. Other than these common elements, molluscs express great morphological diversity, so many textbooks base their descriptions on a "hypothetical ancestral mollusc" (see image below). Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021, A New Voyage Round the World, in the years 1823, 24, 25, and 26, Vol. [105], Some species of molluscs, particularly certain snails and slugs, can be serious crop pests,[106] and when introduced into new environments, can unbalance local ecosystems. This has a single, "limpet-like" shell on top, which is made of proteins and chitin reinforced with calcium carbonate, and is secreted by a mantle covering the whole upper surface. Other Words from mollusk Example Sentences Learn More about mollusk. The radula primarily functions to scrape bacteria and algae off rocks, and is associated with the odontophore, a cartilaginous supporting organ. Medical Dictionary, © 2009 Farlex and Partners. Around 85,000 extant species of molluscs are recognized. They also occur in freshwater and on land. Pronunciation of Mollusca and its etymology. It is lined with epidermis, and is exposed, according to habitat, to sea, fresh water or air. A possible "family tree" of molluscs (2007). The main body cavity is a hemocoel through which blood circulates; as such, their circulatory systems are mainly open. 3.52. [15] The atria of the heart also function as part of the excretory system by filtering waste products out of the blood and dumping it into the coelom as urine. Kimberella, from about 555 million years ago, has been described by some paleontologists as "mollusc-like",[47][48] but others are unwilling to go further than "probable bilaterian",[49][50] if that. Molluscs have, for centuries, also been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye, and sea silk. A pair of nephridia ("little kidneys") to the rear of and connected to the coelom extracts any re-usable materials from the urine and dumps additional waste products into it, and then ejects it via tubes that discharge into the mantle cavity.[15]. See more. A risk of food poisoning exists from toxins that can accumulate in certain molluscs under specific conditions, however, and because of this, many countries have regulations to reduce this risk. [74] A 2010 analysis recovered the traditional conchiferan and aculiferan groups, and showed molluscs were monophyletic, demonstrating that available data for solenogastres was contaminated. & Rolán, E., ed. [50] In one particular branch of the family tree, the shell of conchiferans is thought to have evolved from the spicules (small spines) of aplacophorans; but this is difficult to reconcile with the embryological origins of spicules. Eventually, the larva sinks to the seafloor and metamorphoses into the adult form. ; García-Álvarez, O.L. What does molluscs mean? Mollusca. [54], However, the Helcionellids, which first appear over 540 million years ago in Early Cambrian rocks from Siberia and China,[55][56] are thought to be early molluscs with rather snail-like shells. Why Do “Left” And “Right” Mean Liberal And Conservative? The main body cavity is a hemocoel through which blood and coelomic fluid circulate and which encloses most of the other internal organs. Some such as the scallops have eyes around the edges of their shells which connect to a pair of looped nerves and which provide the ability to distinguish between light and shadow. Mollusca live two hundred fathoms down in the Norwegian seas. : any of a large phylum (Mollusca) of invertebrate animals (such as snails, clams, or squids) with a soft unsegmented body usually enclosed in a calcareous shell broadly : shellfish. Generally, the gills are rather like feathers in shape, although some species have gills with filaments on only one side. The "generalized" mollusc's feeding system consists of a rasping "tongue", the radula, and a complex digestive system in which exuded mucus and microscopic, muscle-powered "hairs" called cilia play various important roles. Journal of Molluscan Studies. Although highly diverse, all members of the phylum share certain general features. The monoplacophoran Neopilina uses its radula in the usual fashion, but its diet includes protists such as the xenophyophore Stannophyllum. As now known, these groups have no relation to molluscs, and very little to one another, so the name Molluscoida has been abandoned. Other characteristics that commonly appear in textbooks have significant exceptions: Estimates of accepted described living species of molluscs vary from 50,000 to a maximum of 120,000 species. Most material © 2005, 1997, 1991 by Penguin Random House LLC. The simplest molluscan reproductive system relies on external fertilization, but with more complex variations. Originally: a heterogeneous group of mostly shell-less invertebrates, forming the second order of the class Vermes in Linnaeus's classification (Systema Naturae (ed. Hypernyms ("Mollusca" is a kind of...): phylum ((biology) the major taxonomic group of animals and plants; contains classes). Most pairs of corresponding ganglia on both sides of the body are linked by commissures (relatively large bundles of nerves). Budd, G. E., and S. Jensen. Bivalvia, formerly called Lamellibranchiata, or Conchifera). [29] Image courtesy of Jan Delsing, Wikimedia Commons The phylum Mollusca is the second-largest animal phylum, with over 100,000 species. They have an open circulatory system and kidney-like organs for excretion. [12], The cephalic molluscs have two pairs of main nerve cords organized around a number of paired ganglia, the visceral cords serving the internal organs and the pedal ones serving the foot. [87], Other luxury and high-status products were made from molluscs. Carnivorous molluscs usually have simpler digestive systems. [38] Sacoglossan sea-slugs suck the sap from algae, using their one-row radula to pierce the cell walls,[39] whereas dorid nudibranchs and some Vetigastropoda feed on sponges[40][41] and others feed on hydroids. Related words - Mollusca synonyms, antonyms, hypernyms and hyponyms. Cephalopod molluscs, such as squid, cuttlefish, and octopuses, are among the most neurologically advanced of all invertebrates—and either the giant squid or the colossal squid is the largest known invertebrate species. Most mollusk species grow a hard shell for … Tentaculita may also be in Mollusca (see Tentaculites). The Most Surprisingly Serendipitous Words Of The Day. They include snails, slugs and other gastropods; clams and other bivalves; squids and other cephalopods; and other lesser-known but similarly distinctive subgroups. [12] The following are present in all modern molluscs:[13][15]. the act of a person who encloses something in or as if in a casing or covering. Many molluscs live in…. Most molluscs with shells can produce pearls, but only the pearls of bivalves and some gastropods, whose shells are lined with nacre, are valuable. [1] In 1969 David Nicol estimated the probable total number of living mollusc species at 107,000 of which were about 12,000 fresh-water gastropods and 35,000 terrestrial. A number of species of molluscs can bite or sting humans, and some have become agricultural pests. (mŏl-lŭs′kă) A phylum of animals that includes the bivalves (mussels, oysters, clams), slugs, and snails. Molluscs, especially bivalves such as clams and mussels, have been an important food source since at least the advent of anatomically modern humans, and this has often resulted in overfishing. Although molluscs are coelomates, the coelom tends to be small. Most of them are marine. The simplest type of molluscan reproductive system relies on external fertilization, but more complex variations occur. Mollusca: 1 n gastropods; bivalves; cephalopods; chitons Synonyms: phylum Mollusca Type of: phylum (biology) the major taxonomic group of animals and plants; contains classes [15], As the head has largely disappeared in bivalves, the mouth has been equipped with labial palps (two on each side of the mouth) to collect the detritus from its mucus. CS1 maint: bot: original URL status unknown (, "Phylogeny and taxonomy of the Kermia–Pseudodaphnella (Mollusca: Gastropoda: Raphitomidae) genus complex: A remarkable radiation via diversification of larval development", "Evidence for a clade composed of molluscs with serially repeated structures: monoplacophorans are related to chitons", "First-ever observations of a live giant squid in the wild", "The global decline of nonmarine mollusks", 10.1641/0006-3568(2004)054[0321:TGDONM]2.0.CO;2, "A comparative study of the ultrastructure and mineralogy of calcified land snail eggs (Pulmonata: Stylommatophora)", "How the Pacific Oyster Responds to Ocean Acidification: Development and Application of a Meta-Analysis Based Adverse Outcome Pathway", "Xenophyophores (Protozoa, Sarcodina) in the diet of, "Coexistence of hydroid-eating Nudibranchs: Do feeding biology and habitat use matter? One such pest, the giant African snail Achatina fulica, has been introduced to many parts of Asia, as well as to many islands in the Indian Ocean and Pacific Ocean. a school giving instruction in one or more of the fine or dramatic arts. [61] The Late Cambrian fossil Plectronoceras is now thought to be the earliest clearly cephalopod fossil, as its shell had septa and a siphuncle, a strand of tissue that Nautilus uses to remove water from compartments it has vacated as it grows, and which is also visible in fossil ammonite shells. 1. molluscum [n] - See also: molluscum. This animal is a genus of the mollusca tribe, which glitters in the night on the crest of every bursting wave. [58] However, other scientists are not convinced these Early Cambrian fossils show clear signs of the torsion that identifies modern gastropods twists the internal organs so the anus lies above the head. Definition of Mollusca. [63] However, the shell-less Coleoidea (squid, octopus, cuttlefish) are abundant today.[64]. [42] (An extensive list of molluscs with unusual feeding habits is available in the appendix of .mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}GRAHAM, A. Phylum Mollusca: several classes, in particular Gastropoda, Bivalvia, and Cephalopoda 1790–1800;