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Atlanta (genus)
Encyclopedia
Atlanta is a genus
of pelagic marine
gastropod molluscs in the family
Atlantidae
. They are sometimes called heteropods.
, 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.
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 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).
, 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.
de Vera & Seapy, 2006.
Species in the genus Atlanta include:
Based on similar morphologies, these species have been placed in seven species group
s:
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).
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of pelagic marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
gastropod molluscs in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Atlantidae
Atlantidae
Atlantidae is a family of sea snails, holoplanktonic gastropod molluscs in the clade Littorinimorpha.According to taxonomy of the Gastropoda by Bouchet & Rocroi the family Atlantidae has no subfamilies.- Description :...
. They are sometimes called heteropods.
Distribution
All of the nineteen species but one, Atlanta californiensisAtlanta californiensis
Atlanta californiensis is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.-External links:*...
, 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
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
shell has a diameter of less than 1 cm. The protoconch
Protoconch
A protoconch is an embryonic or larval shell of some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod...
of the larval shell is retained after metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
and becomes the spire
Spire (mollusc)
A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
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
Operculum (gastropod)
The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...
. 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 in pigmented region between the lens and the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
.
The radula
Radula
The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...
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, radulaRadula
The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...
, operculum
Operculum (gastropod)
The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...
) 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
Protoconch
A protoconch is an embryonic or larval shell of some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod...
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
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
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 selvagensisAtlanta selvagensis
Atlanta selvagensis is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
de Vera & Seapy, 2006.
Species in the genus Atlanta include:
- † Atlanta arenularia Gougerot & Braillon, 1965 - this is the oldest known Atlanta from the BartonianBartonianThe Bartonian is, in the ICS's geological timescale, a stage or age in the middle Eocene epoch or series. The Bartonian age spans the time between and . It is preceded by the Lutetian and is followed by the Priabonian age.-Stratigraphic definition:...
of the Paris Basin - Atlanta brunneaAtlanta brunneaAtlanta brunnea is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.-Description:Atlanta brunnea is a small species that is darkly pigmented . The keel is tall and colorless, and inserts between the last and penultimate shell whorls in animals larger than...
J. E. Gray, 1850 - synonym: Atlanta fusca Eydoux & F. L. A. Souleyet, 1852 - Atlanta californiensisAtlanta californiensisAtlanta californiensis is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.-External links:*...
Seapy & Richter, 1993 - Atlanta echinogyraAtlanta echinogyraAtlanta echinogyra is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.-Description:Atlanta echinogyra was described in 1972 by Dr. Gotthard Richter based on specimens collected during the Meteor Expedition to the northern Indian Ocean...
Richter, 1972 - Atlanta fragilisAtlanta fragilisAtlanta fragilis is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Richter, 1993 - Atlanta frontieri Richter, 1993
- Atlanta gaudichaudi Souleyet, 1852
- Atlanta gibbosaAtlanta gibbosaAtlanta gibbosa is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Souleyet, 1852 - Atlanta helicinoideaAtlanta helicinoideaAtlanta helicinoidea is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
J. E. Gray, 1850 - Atlanta inclinataAtlanta inclinataAtlanta inclinata is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
J. E. Gray, 1850 - Atlanta inflataAtlanta inflataAtlanta inflata is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
J. E. Gray, 1850 - Atlanta lesueuriiAtlanta lesueuriiAtlanta lesueurii is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.-Description:The maximal shell size of Atlanta lesueurii appears to vary geographically...
J. E. Gray, 1850 - † Atlanta lingayanensis Janssen, 2007 - from Pliocene of Philippines
- Atlanta meteoriAtlanta meteoriAtlanta meteori is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Richter, 1972 - Atlanta oligogyraAtlanta oligogyraAtlanta oligogyra is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Tesch, 1906 - Atlanta peroniiAtlanta peroniiAtlanta peronii is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Lesueur, 1817 - Atlanta planaAtlanta planaAtlanta plana is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Richter, 1972 - Atlanta pulchellaAtlanta pulchellaAtlanta pulchella is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.-Distribution:Distribution of Atlanta pulchella include North West Atlantic: off Massachusetts and Delaware....
Verrill, 1884 - Atlanta quoyanaAtlanta quoyanaAtlanta quoyana is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Smith, 1888 - Atlanta quoyiiAtlanta quoyiiAtlanta quoyii is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Gray, 1850 - † Atlanta richteri Janssen, 2007 - from Pliocene of Philippines
- Atlanta roseaAtlanta roseaAtlanta rosea is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
Souleyet, 1852 - † Atlanta seapyi Janssen, 2007 - from Pliocene of Philippines
- Atlanta selvagensisAtlanta selvagensisAtlanta selvagensis is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
de Vera & Seapy, 2006 - Atlanta tokiokaiAtlanta tokiokaiAtlanta tokiokai is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
van der Spoel & Troost, 1972 - Atlanta turriculataAtlanta turriculataAtlanta turriculata is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
d'Orbigny, 1836
Based on similar morphologies, these species have been placed in seven species group
Species group
A species group is an informal taxonomic rank into which an assemblage of closely related species within a genus are grouped because of their morphological similarities and their identity as a biological unit with a single monophyletic origin.-Use:...
s:
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).