''Atlanta'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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 ...

marine

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

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 ...

Atlantidae Atlantidae is a family of sea snails, holoplanktonic gastropod molluscs in the clade Littorinimorpha. According to taxonomy of the Gastropoda by Bouchet & Rocroi (2005) the family Atlantidae has no subfamilies. Description The Atlantidae is a ...

. They are sometimes called heteropods.Bouchet, P.; Gofas, S. (2012). Atlanta. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=137687 on 2012-07-18

Distribution

All of the nineteen species but one, '' Atlanta californiensis'', dwell in

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

and

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones immediately to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Ge ...

waters. The majority of species (ten) are cosmopolitan and, among the remaining nine species, five are Indo-Pacific, two are restricted to the Pacific Ocean, one is Indo-Atlantic, and one is limited to the Atlantic Ocean. They are floating or swimming snails in tropical and subtropical seas. Most have a cosmopolitan distribution, but ''A. brunnea'', ''A. pulchella'' and ''A. quoyi'' are only found in American waters. ''A. fusca'', ''A. pacifica'' and ''A. rosea'' are restricted the seas around Japan.

Description

It has been recognized by several authors that identification of species in this genus is difficult and is dependent on their morphology of eyes, radula and operculum. Main diagnostic features include: the shell and keel are calcareous; larval shell becomes the spire in the adult shell. Snails of this genus are very small. Their coiled,

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

shell has a diameter of less than 1 cm. The

protoconch A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called " ...

of the larval shell is retained after

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

and becomes the

spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spire ...

of the adult shell. The number of spire whirls varies from 2½ (in the ''A. lesueuri''- group) to 6 (''A. gibbosa'') and is thus also helpful in the identification of a species. The spire shape differs between the species groups, from very small (''A. lesueuri''- group), to inflated or flat (''A. inflata''- group ) to large (''A.inclinata''- group and ''A. gibbosa''- group). They can retract into their shell and close it off with an operculum. This operculum is

cartilaginous Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

and flexible. In 1961 Richter distinguished three types of the operculum in which the larval gyre of the operculum is apical. This gyre can be relatively somewhat larger (macro-oligogyre), smaller (micro-oligogyre) or a single gyre (monogyre). The eye morphology also consists of three types with differences in pigmented region between the lens and the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

. The

radula The radula (; : radulae or radulas) is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters ...

is typically taenioglossate with one central (rachidian) tooth, with on each side one lateral tooth and two marginal teeth. In 13 species the number of tooth rows increases during growth (Type I), while in 8 species the radula has a limited number of tooth rows (Type II).

Identification

Many authors (e.g., Thiriot-Quiévreux, 1973, p. 240; Richter, 1974, p. 60; Seapy, 1990, p. 107) admit that identification of Atlanta species is difficult and including soft-part features (eyes,

, operculum) or application of transmitted light to observe inner shell structures (Richter, 1987, p. 178) are very helpful in distinguishing species with similar shells. However, such methods are unavailable for fossil material. This makes identifying fossil species of ''Atlanta'' quite difficult and even well-preserved specimens occasionally can only be related to existing taxa with a query (e.g., ''Atlanta'' sp. in Janssen, 2004, p. 108; ''Atlanta'' cf. ''echinogyra'' in Jansen 2007). Advantageous in this study of fossil atlantids, however, is the fact that all specimens are preserved as opaque aragonitic shells as a result of recrystallisation, which facilitates assessing

shape and ornament with a normal 25 or 50× binocular magnification, they are thus much easier studied than in the usually very transparent and shiny Recent specimens. Still, here, too, study of the larval shell shape and micro-ornamentation by

SEM SEM or Sem can refer to: Computing * Search engine marketing, promoting websites by increasing their visibility in search engine results * Security event manager, a security log tool used on data networks Economics and management * Stock Ex ...

is highly desirable or even indispensable.

Species

''Atlanta'' includes a large number of Recent species. Lalli & Gilmer (1989) listed 14 species, but Richter & Seapy (1999) recognised 21 extant species, provisionally subdivided into seven 'species groups' (and one species unassigned). A further Recent species was described since; '' Atlanta selvagensis'' de Vera & Seapy, 2006. Species in the genus ''Atlanta'' include: *† '' Atlanta arenularia'' Gougerot & Braillon, 1965 - this is the oldest known Atlanta 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 * '' Atlanta brunnea'' J. E. Gray, 1850 - synonym: ''Atlanta fusca'' Eydoux & F. L. A. Souleyet, 1852 * '' Atlanta californiensis'' Seapy & Richter, 1993 * '' Atlanta echinogyra'' Richter, 1972 * '' Atlanta fragilis'' Richter, 1993 * '' Atlanta frontieri'' Richter, 1993 * '' Atlanta gaudichaudi'' Souleyet, 1852 * '' Atlanta helicinoidea'' J. E. Gray, 1850 * '' Atlanta inclinata'' J. E. Gray, 1850 * '' Atlanta inflata'' J. E. Gray, 1850 * ''

Atlanta lesueurii ''Atlanta lesueurii'' is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity ( ...

'' J. E. Gray, 1850 * † '' Atlanta lingayanensis'' Janssen, 2007 - from Pliocene of Philippines * '' Atlanta meteori'' Richter, 1972 * '' Atlanta oligogyra'' Tesch, 1906 * '' Atlanta peronii'' Lesueur, 1817 *'' Atlanta plana'' Richter, 1972 * '' Atlanta pulchella'' Verrill, 1884 * '' Atlanta quoyii'' Gray, 1850 * † '' Atlanta richteri'' Janssen, 2007 - from Pliocene of Philippines * '' Atlanta rosea'' Souleyet, 1852 * † '' Atlanta seapyi'' Janssen, 2007 - from Pliocene of Philippines * '' Atlanta selvagensis'' de Vera & Seapy, 2006 * '' Atlanta tokiokai'' van der Spoel & Troost, 1972 * '' Atlanta turriculata'' d'Orbigny, 1836 ;Species brought into synonymy: * Subgenus ''Atlanta (Heliconoides)'' d'Orbigny, 1835: synonym of '' Heliconoides'' d'Orbigny, 1835 * ''Atlanta bulimoides'' d'Orbigny, 1834: synonym of '' Limacina bulimoides'' (d'Orbigny, 1834) * ''Atlanta fusca'' Souleyet, 1852: synonym of ''Atlanta brunnea'' J. E. Gray, 1850 * ''Atlanta gaudichaudii'' Souleyet, 1852: synonym of ''Atlanta gaudichaudi'' J. E. Gray, 1850 * ''Atlanta gibbosa'' Souleyet, 1852: synonym of ''Atlanta inclinata'' J. E. Gray, 1850 * ''Atlanta helicinoides'' Souleyet, 1852: synonym of ''Atlanta helicinoidea'' J. E. Gray, 1850 * ''Atlanta inclinata'' Souleyet, 1852: synonym of ''Atlanta inclinata'' J. E. Gray, 1850 * ''Atlanta inflata'' Souleyet, 1852: synonym of ''Atlanta inflata'' J. E. Gray, 1850 * ''Atlanta inflata'' d'Orbigny, 1834: synonym of '' Heliconoides inflata'' (d'Orbigny, 1834) * ''Atlanta lamanoni'' Gray, 1850: synonym of ''

Protatlanta souleyeti ''Protatlanta souleyeti'' is a species of sea snail, a holoplanktonic marine (ocean), marine gastropod mollusk in the family (biology), family Atlantidae. ''Protatlanta souleyeti'' is the type species on the genus ''Protatlanta''. It is conside ...

'' (E. A. Smith, 1888) * ''Atlanta lesueurii'' Souleyet, 1852: synonym of ''Atlanta lesueurii'' J. E. Gray, 1850 * ''Atlanta lesueurii'' d'Orbigny, 1835: synonym of '' Limacina lesueurii'' (d'Orbigny, 1835) * ''Atlanta quoyana'' Smith, 1888: synonym of ''Atlanta quoyii'' J. E. Gray, 1850 * ''Atlanta steindachneri'' Oberwimmer, 1898: synonym of ''Atlanta peronii'' Lesueur, 1817 * ''Atlanta trochiformis'' d'Orbigny, 1834: synonym of '' Limacina trochiformis'' (d'Orbigny, 1834) Based on similar morphologies, these species have been placed in seven

species group In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

s:Richter G. & Seapy R. R. (1999). Heteropoda. In: D. Boltovskoy (ed.). South Atlantic zooplankton, 1. Backhuys, Leiden; p. 621-647. Tesch (1908) was the first to group together the species of ''Atlanta'' sharing similar morphologies. He recognized four species groups; the ''Atlanta peronii''-, ''Atlanta inflata''-, ''Atlanta turriculata''-, and ''Atlanta inclinata''-groups. In addition to these four, three additional ones are currently recognized; the ''Atlanta lesueurii''-, ''Atlanta gaudichaudi''- and ''Atlanta gibbosa'' groups. Except for Tesch's ''Atlanta turriculata''-group, the composition of Tesch's species groups has changed by species invalidations, the addition of new species over time, and addition of three new species groups. The main changes in Tesch's species groups have occurred in the ''Atlanta peronii''-group (with ''Atlanta gaudichaudi'' and ''Atlanta lesueurii'' now forming their own species groups) and the ''Atlanta inclinata''-group (the ''Atlanta gibbosa'' now forming its own group).

References

This article incorporates CC BY-3.0 text from references.Seapy R. R. (2010)
''Atlanta''
Version 17 July 2010.

Tree of Life Web Project The Tree of Life Web Project (ToL) is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The s ...

, accessed 19 August 2010. * Richter G. & Seapy R.R. 1999. ''Heteropoda'', pp. 621–647. In: D. Boltovskoy (ed.), South Atlantic Zooplankton. Leiden: Backhuys Publ. * Gofas, S.; Le Renard, J.; Bouchet, P. (2001). Mollusca, in: Costello, M.J. et al. (Ed.) (2001). ''European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification''. Collection Patrimoines Naturels, 50: pp. 180–213 * Rolán E., 2005. ''Malacological Fauna From The Cape Verde Archipelago. Part 1, Polyplacophora and Gastropoda''. * Rosenberg, G., F. Moretzsohn, and E. F. García. 2009. ''Gastropoda (Mollusca) of the Gulf of Mexico'', Pp. 579–699 in Felder, D.L. and D.K. Camp (eds.), Gulf of Mexico–Origins, Waters, and Biota. Biodiversity. Texas A&M Press, College Station, Texas. * Spencer, H.; Marshall. B. (2009). ''All Mollusca except Opisthobranchia''. In: Gordon, D. (Ed.) (2009). New Zealand Inventory of Biodiversity. Volume One: Kingdom Animalia. 584 pp

External links

Marco Oliverio, ''Gastropoda Prosobranchia'', Biol. Mar. Mediterr. (2008), 15 (suppl.): 235–278

Oliverio, Marco (2006). ''Gastropoda Prosobranchia Caenogastropoda'', in: Revisione della Checklist della fauna marina italiana
{{Authority control Atlantidae Bartonian first appearances Extant Eocene first appearances