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''Calliostoma'' is a genus of small to medium-sized sea snails with gills and an operculum, marine gastropod molluscs within the family Calliostomatidae, the calliostoma top snails (according to the taxonomy of taxonomy of Gastropoda by Bouchet & Rocroi (2005)). Previously this genus was placed within the family Trochidae. ''Calliostoma'' is the type genus of the family Calliostomatidae. The name of this genus is derived from the Greek words ''kallos'' (beautiful) and ''stoma'' (mouth), referring to the pearly aperture of the shell. The genus ''Calliostoma'' is known in fossil records from the Upper Cretaceous onwards.〔Shimer & Shrock (1944). ''Index fossils of North America''.〕 The distribution of this genus is worldwide, found mainly on hard substrata, although Japanese species have been found on sandy bottoms. These snails occur from shallow waters to bathyal depths. The species in this genus are mainly herbivorous or feed on detritus,〔Clench W. & Turner R. (1960). "The genus ''Calliostoma'' in the western Atlantic". ''Johnsonia'' 4(40) :1-80.〕 although a few have been observed to be omnivorous (Keen, 1975) or even carnivorous, feeding on a wide range of algae and on animals belonging to various other invertebrate phyla. The North Atlantic topshell ''Calliostoma occidentale'' has been reported to feed on coelenterates. Contrary to what is the case in most other top shells, ''Calliostoma'' deposits its eggs in gelatinous ribbons that are only fertilized ''after'' being deposited. The young emerge as small snails (Lebour, 1936) without passing through a free-living planktonic stage as a veliger larva. ==Description== The rather thin, acute, coeloconoid (= approaching conical shape but with concave sides) shell is imperforate or rarely umbilicate. The whorls are smooth, often polished and spirally ridged or granular. The body whorl is angulated at the periphery. The aperture is quadrangular, sinuated at the base and slightly oblique. The columella is simple, usually ending anteriorly in a slight tooth.〔(Tryon (1889), Manual of Conchology XI, Academy of Natural Sciences, Philadelphia )〕 The nucleus appears to be either dextral or sinistral indifferently.〔(Dall W. H. 1889. Reports on the results of dredging, under the supervision of Alexander Agassiz, in the Gulf of Mexico (1877-78) and in the Caribbean Sea (1879-80), by the U.S. Coast Survey Steamer "Blake", Lieut.-Commander C.D. Sigsbee, U.S.N., and Commander J.R. Bartlett, U.S.N., commanding. XXIX. Report on the Mollusca. Part 2, Gastropoda and Scaphopoda. Bulletin of the Museum of Comparative Zoölogy at Harvard College 18: 1-492, pls. 10-40 )〕〔(Swainson, W. 1840. ''A treatise on malacology, or shells and shell-fish''; London )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Calliostoma」の詳細全文を読む スポンサード リンク
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