Atlanta (gastropod)

Atlanta is a genus of pelagic marine gastropod molluscs in the family Atlantidae.

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 the species but one, Atlanta californiensis, dwell in tropical and subtropical 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 shell has a diameter of less than 1 cm. The protoconch of the larval shell is retained after metamorphosis and becomes the 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 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 radula 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 The Atlanta, whose discovery dates back to the La Pérouse expedition and which were so named by Mr. Lesueur—though Mr. Rang was the first to make their true characteristics known—complete the series of Heteropods. They link these mollusks to the Gastropods, whose entire conformation they share, as we have previously seen.

The Atlanta do not differ as much from the Carinaria Lamarck, 1801 as one might believe at first glance; one can even form a very accurate idea of them by imagining them as Carinaria whose bodies, while retaining their shape, have been reduced in proportion, and whose shells have simultaneously achieved a development large enough for the animal to retract into them entirely. The branchial cavity with which they are provided, and the slightly different termination of the intestine and the oviduct within this cavity, are evidently nothing more than the result of this shell development, which has brought about an analogous development in the corresponding part of the mantle.

Finally, the ability of the Atlanta to shelter themselves completely within their shells further explains the presence in these mollusks of an operculum, arranged exactly as it is in Gastropods with turbinate shells.

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, radula, 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 protoconch 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 is highly desirable or even indispensable.

Species Atlanta includes a large number of Recent species. Lalli & Gilmer (1989)Lalli C. M. & Gilmer R. W. (1989). Pelagic Snails. The Biology of Holoplanktonic Gastropod Mollusks. Stanford University Press, Stanford, California: viii + 259 pp. page 52. listed 14 species, but Richter & Seapy (1999)Richter G. & Seapy R. R. (1999). "Heteropoda". In: D. Boltovskoy (ed.) South Atlantic zooplankton, 1. Backhuys, Leiden: 621–647. page 631. 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 of the Paris Basin Atlanta ariejansseni Wall-Palmer, Burridge & Peijnenburg, 2016 Atlanta brunnea J. E. Gray, 1850WoRMS (2010). Atlanta brunnea J. E. Gray, 1850. In: Bouchet, P.; Gofas, S.; Rosenberg, G. (2010) World Marine Mollusca database. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=238118 on 2010-08-19 Atlanta californiensis Seapy & Richter, 1993WoRMS (2009). Atlanta californiensis Seapy & Richter, 1993. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430414 on 2010-08-19 † Atlanta diamesa Woodring, 1928 Atlanta echinogyra Richter, 1972WoRMS (2009). Atlanta echinogyra Richter, 1972. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430420 on 2010-08-19 † Atlanta eocenica K. van W. Palmer, 1937 Atlanta fragilis Richter, 1993Gofas, S. (2009). Atlanta fragilis Richter, 1993. In: Bouchet, P.; Gofas, S.; Rosenberg, G. World Marine Mollusca database. Accessed through the World Register of Marine Species at http://marinespecies.org/aphia.php?p=taxdetails&id=244556 on 2010-08-19 Atlanta frontieri Richter, 1993Seapy R. R. (2010). Atlanta frontieri Richter 1993. Version 31 January 2010 (under construction). http://tolweb.org/Atlanta_frontieri/28758/2010.01.31 in The Tree of Life Web Project, accessed 19 August 2010. † Atlanta funicularis Garvie, 2013 Atlanta gaudichaudi Souleyet, 1852WoRMS (2009). Atlanta gaudichaudi J. E. Gray, 1850. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430418 on 2010-08-19 Atlanta gibbosa Souleyet, 1852 Atlanta helicinoidea J. E. Gray, 1850WoRMS (2009). Atlanta helicinoidea J. E. Gray, 1850. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=419791 on 2010-08-19 Atlanta inclinata J. E. Gray, 1850WoRMS (2009). Atlanta inclinata J. E. Gray, 1850. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430422 on 2010-08-19 † Atlanta indoceratoides Beets, 1942 Atlanta inflata J. E. Gray, 1850WoRMS (2009). Atlanta inflata J. E. Gray, 1850. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430413 on 2010-08-19 Atlanta involuta Souleyet, 1852 Atlanta lesueurii J. E. Gray, 1850WoRMS (2010). Atlanta lesueurii J. E. Gray, 1850. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430416 on 2010-08-19 † Atlanta lingayanensis Janssen, 2007 - from Pliocene of Philippines Atlanta meteori Richter, 1972WoRMS (2009). Atlanta meteori Richter, 1972. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430425 on 2010-08-19 † Atlanta oanei Stancu, 1978 Atlanta oligogyra Tesch, 1906WoRMS (2009). Atlanta oligogyra Tesch, 1806. In: Bouchet, P.; Gofas, S.; Rosenberg, G. (2009) World Marine Mollusca database. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=244554 on 2010-08-19 Atlanta peronii Lesueur, 1817Gofas, S. (2009). Atlanta peronii Lesueur, 1817. In: Bouchet, P.; Gofas, S.; Rosenberg, G. (2009) World Marine Mollusca database. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=138838 on 2010-08-19 Atlanta plana Richter, 1972WoRMS (2009). Atlanta plana Richter, 1972. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430419 on 2010-08-19 Atlanta pulchella Verrill, 1884Rosenberg, G. (2010). Atlanta pulchella A. E. Verrill, 1884. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=160169 on 2010-08-19 (taxon inquirendum) † Atlanta richteri Janssen, 2007 - from Pliocene of Philippines Atlanta rosea Gray, 1850Gofas, S. (2009). Atlanta rosea Souleyet, 1852. In: Bouchet, P.; Gofas, S.; Rosenberg, G. World Marine Mollusca database. Accessed through the World Register of Marine Species at http://marinespecies.org/aphia.php?p=taxdetails&id=238120 on 2010-08-19 † Atlanta seapyi Janssen, 2007 - from Pliocene of Philippines Atlanta selvagensis de Vera & Seapy, 2006 Atlanta tokiokai van der Spoel & Troost, 1972WoRMS (2009). Atlanta tokiokai van der Spoel and Troost, 1972. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430423 on 2010-08-19 Atlanta turriculata d'Orbigny, 1836WoRMS (2009). Atlanta turriculata d'Orbigny 1835. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430412 on 2010-08-19 Atlanta vanderspoeli Wall-Palmer, Hegmann & Peijnenburg, 2019

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 cordiformis Gabb, 1873: synonym of Atlanta selvagensis de Vera & Seapy, 2006 Atlanta depressa Gray, 1850: synonym of Atlanta helicinoidea J. E. Gray, 1850 (doubtful synonym) 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 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 keraudrenii Lesueur, 1817: synonym of Atlanta peronii Lesueur, 1817 Atlanta lamanoni Gray, 1850: synonym of Protatlanta souleyeti (E. A. Smith, 1888) Atlanta lamanonii Souleyet, 1852: synonym of Protatlanta souleyeti (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)