Atlantidae is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

sea snail Sea snails are slow-moving marine (ocean), marine gastropod Mollusca, molluscs, usually with visible external shells, such as whelk or abalone. They share the Taxonomic classification, taxonomic class Gastropoda with slugs, which are distinguishe ...

holoplankton Holoplankton are organisms that are 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 their l ...

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s in the

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Littorinimorpha Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails ( marine species), but also including some freshwater snails ( limnic 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 p ...

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

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-Bomb Abomination Absorbing Man Abraxas Abyss Abyss is the name of two characters appearing in Ameri ...

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 ass ...

(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 List of capitals in the United States, capital and List of municipalities in Georgia (U.S. state), most populous city in the U.S. state of Georgia (U.S. state), Georgia. It is the county seat, seat of Fulton County, Georg ...

'' 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 "unispe ...

. 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 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

), ''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 International Commission on Stratigraphy's (ICS) geologic time scale, a stage or age in the middle of the Eocene Epoch or Series. The Bartonian Age spans the time between . It is preceded by the Lutetian and is follow ...

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 fluid, serous and muc ...

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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