''Calliostoma'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of small to medium-sized sea snails with

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...

s and an operculum, marine gastropod molluscs within the family Calliostomatidae, the Calliostoma top snails. Previously this genus was placed within the family Trochidae. ''Calliostoma'' is the type genus of the family Calliostomatidae.

Taxonomy

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. As of 2022, ''Calliostoma'' is treated as a very broad genus of about 300 accepted species. While current information is too fragmentary to assign all species in a revised genus, it is expected to be broken up and (some) subgenera will be elevated to the status of genus. A complete listing can be found at the list of ''Calliostoma'' species.

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 Lucius Junius Moderatus Columella (; Arabic: , 4 – ) was a prominent writer on agriculture in the Roman Empire. His ' in twelve volumes has been completely preserved and forms an important source on Roman agriculture, together with the ...

is simple, usually ending anteriorly in a slight tooth. The nucleus appears to be either dextral or sinistral indifferently.

Distribution and habitat

The distribution of this genus is worldwide, found mainly on hard substrates, although Japanese species have been found on sandy bottoms. These snails occur from shallow waters to bathyal depths.

Behaviour and ecology

The species in this genus are mainly herbivorous or feed on detritus, although a few have been observed to be omnivorous (Keen, 1975) or even carnivorous, feeding on a wide range of

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and on animals belonging to various other

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

phyla Phyla, the plural of ''phylum'', may refer to: * Phylum, a biological taxon between Kingdom and Class * by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another Phyl ...

. The North Atlantic topshell '' Calliostoma occidentale'' has been reported to feed on coelenterates. Contrary to what is the case in most other top shells, species of the genus ''Calliostoma'' deposits their 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

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...

ic stage as a

veliger A veliger is the planktonic larva of many kinds of sea snails and freshwater snails, as well as most bivalve molluscs (clams) and tusk shells. Description The veliger is the characteristic larva of the gastropod, bivalve and scaphopod ...

larva.

Gallery

File:Calliostoma bairdii drawing.jpg, Drawing of a dorsal view of a living animal of ''

Calliostoma bairdii ''Calliostoma bairdii'', common name the Baird's top shell, is a species of sea snail with an operculum, a marine gastropod mollusk in the family Calliostomatidae, the calliostoma top snails.Rosenberg, G. (2010). ''Calliostoma bairdii'' Verril ...

'' dredged in the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...

at a depth of from 100 m to 1170 m Calliostoma supragranosum.jpg, Rare purple beaded specimen of ''Calliostoma supragranosum'' found subtidally in

Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban ...

References