Atlantidae is a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

holoplankton Holoplankton are organisms that are plankton, planktic (they live in the water column and cannot swim against a current) for their entire life cycle. Holoplankton can be contrasted with meroplankton, which are planktic organisms that spend part of ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s in the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

Littorinimorpha Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails ( marine species), but also including some freshwater snails ( aquatic species) and land snails (terrestrial species).Bouchet P. & Rocroi J.-P. (Ed.); Fr� ...

. According to taxonomy of the Gastropoda by Bouchet & Rocroi (2005) the family Atlantidae has no subfamilies.

Description

The Atlantidae is a group of holoplanktonic gastropods, which all demonstrate a strong

adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

life, in the form of a lenticular, laterally flattened, aragonitic shell, the surface of which is further enlarged by the presence of a wide, and very thin and fragile, double-walled keel. The apex is on the right side of the shell, the umbilicus on the left. For the living animal the enlargement of the shell’s surface serves ‘to increase stabilization during swimming and sinking’. This phenomenon results in the occurrence of superficially very similar adult shells in separate species, whereas the larval shells may be utterly different. Their body size is microscopic with a shell diameter of less than 1 cm. The foot has evolved into a muscular swimming fin. Their swimming fin extends anteriorly beneath their head. They swim with their ventral part upward through undulation of their swimming fin. The shell is coiled dextrally (i.e. clockwise). The thin, double-walled keel of the shell extends outward from the last shell whorl. The

apex The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics), a teenaged super villainess in the Marvel Universe * Ape-X, a super-intelligent ape in the Squadron Supreme universe *Apex ...

of the shell is found on the right side, the umbilicus on the left side. The shell and keel can be calcareous (genus ''Atlanta''), or composed exclusively of

conchiolin Conchiolins (sometimes referred to as conchins) are complex proteins which are secreted by a mollusc's outer epithelium (the mantle). These proteins are part of a matrix of organic macromolecules, mainly proteins and polysaccharides, that assem ...

(genus Oxygyrus), or the shell can be calcareous and its keel composed of conchiolin (genus ''Protatlanta''). The snails of this family can retract into their shell and close it off with a cartilaginous, flexible operculum.

Genera

Genera in the family Atlantidae include: * ''

Atlanta Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton County, the most populous county in Georgia, but its territory falls in both Fulton and DeKalb counties. With a population of 498,715 ...

'' Lesueur, 1817 - type genus * '' Oxygyrus'' Benson, 1835 - monospecific, it has only one species '' Oxygyrus keraudrenii'' (Lesueur, 1817) * '' Protatlanta'' Tesch, 1908 - monospecific in extant species; a few fossil species have been described * † '' Bellerophina'' d’Orbigny, 1843 * † '' Eoatlanta'' Cossmann, 1888 * † '' Mioatlanta'' di Geronimo, 1974 Recent Atlantidae, in the present concept, comprise three genera, two of which, ''Oxygyrus'' Benson, 1835, and ''Protatlanta'' Tesch, 1908, are considered

monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

. In ''Protatlanta'', however, a few additional fossil species have been described. Both genera are characterised by partially uncalcified (

) shell portions. Additional fossil genera considered to belong in the Atlantidae are ''Bellerophina'' d’Orbigny, 1843 (

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

), ''Eoatlanta'' Cossmann, 1888 (Paleocene-Eocene) and ''Mioatlanta'' di Geronimo, 1974 (Miocene). Only few ''Atlanta'' species are known from the fossil record, the oldest one being '' Atlanta arenularia'' Gougerot & Braillon, 1965 is from the

Bartonian The Bartonian is, in the ICS's geologic time scale, a stage or age in the middle Eocene Epoch or Series. The Bartonian Age spans the time between . It is preceded by the Lutetian and is followed by the Priabonian Age. Stratigraphic definitio ...

of the Paris Basin, which differs considerably from typical ''Atlanta'' by its cornucopia shape.

Ecology

Atlantids are negatively buoyant. During the day, they have to swim to maintain their position. At night they secrete strands of buoyant

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

to which they attach themselves. They are active predator locating their prey visually.

References

This article incorporates CC BY-3.0 text from the reference

External links

Seapy, Roger R. 2008. Atlantidae Rang, 1829. Version 29 December 2008 (under construction); Tree of Life Web Project : Atlantidae
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