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Atlanta

Roger R. Seapy
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Containing group: Atlantidae

Introduction

Atlanta is the type genus of the Atlantidae, containing 20 of the 22 species in the family (the other two genera, Protatlanta and Oxygyrus, are monospecific). All species but one (A. californiensis from the temperate North Pacific) are found in tropical to subtropical waters. Most (12) are cosmopolitan in geographic distribution, although three are Indo-Pacific, two are found only in the Indian Ocean, two only in the Atlantic Ocean, and one in the Pacific Ocean.

Diagnosis

An atlantid with:

Characteristics

  1. Shell and keel calcareous.
  2. Spiral portion of operculum present.

Comments

Species in the genus Atlanta can be grouped together (into species groups) by several morphological features:

  1. Eye types. Three eye morphologies (termed types a, b and c; after Richter, 1961) are present that differ primarily in patterns of pigmentation. Types a and b have a large part of the eye wall that lacks pigment forming a window. These two eye types differ in the absence (type a) or presence (type b) of a narrow transverse slit (extension of the distal part of the window) that almost completely separates distal from proximal pigmentation. Type c lacks a window.
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    Figure. The three types of eye morphologies (a, b and c) in Atlanta. Drawing modified from Richter and Seapy (1999).

    Figure. Two (Types b and c) of the three eye types in Atlanta. Left - Type b eye of Atlanta peroni, Hawaiian waters. Right - Type c eye of Atlanta helicinoides Hawaiian waters . A representative photograph of an animal with a Type a eye is not available. Photographs copyright © 2005 R. Seapy.

  2. Operculum types. Three operculum types (termed Types a, b, c; after Richter, 1961) are found in Atlanta. The third type (c) differs from the first two (a and b) in the number of turns of the spiral (larval) gyre; "single" in the mono-gyre and "a few" in the oligo-gyre opercula. The two types of oligogyre opercula differ in the relative size of the gyre region; hence, the prefixes macro- and micro-.
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    Figure. The three types of opercular morphologies (a, b, c) in Atlanta. The gyre portion (larval) of the operculum is shaded blue. Drawing modified from Richter and Seapy (1999).

  3. Spire whorl number. The shell of Atlanta consists of three sequentially-deposited portions; a dome-shaped embryonic shell (protoconch I), a larval shell (protoconch II) and the adult shell (teleoconch). In postmetamorphic animals, the number of whorls comprising the teleoconch increases with growth, while the number of whorls in the protoconch (forming the spire of the adult shell) is constant. The location on the shell where the protoconch ends and the teleoconch begins is often difficult to determine, but its approximate location is necessary in determining the number of whorls comprising the shell spire. The number of spire whorls varies between two and one-half and six among Atlanta species.
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    Figure. Left: Larval shell of Atlanta plana, Hawaiian waters. Scale bar = 0.1 mm. The embryonic shell (protoconch I) is indicated in yellow. The remainder of the larval shell (protoconch II) is shaded blue. Right: Adult shell of Atlanta plana, Hawaiian waters. Scale bar = 0.5 mm. The embryonic and larval shells are colored blue to distinguish them from the remainder of the shell. Scanning electron micrographs copyright © 2005 R. Seapy.

The 20 species of Atlanta are combined into seven species groups (Richter and Seapy, 1999). The groups are each characterized by similarities in overall shell and shell spire morphologies, and in some cases body coloration. In addition, members of each group usually share the same opercular type and, in many cases, the same eye type. The table below summarizes this information.

Species group Group characteristics Species* Species characteristics Shell diameter (except keel) Number of spire whorls Eye type Opercular type
A. fusca group Shell small with tall, rounded keel; spire strongly elevated and sculptured, with complex ornamentation and a prominent spiral ridge; color darkens with age. A. fusca Spire tall conical; color yellowish-brown to dark brown; circumglobal <2 mm 4 a a
A. turriculata Spire tall  turreted; color yellowish- to reddish-brown  grading into clear outer shell whorl; Indo-Pacific. <2 mm 4-1/4 a a
A. inflata group Shell either inflated (width ca. 40% of shell diameter) or flat; spire large (relative to shell size) and low with shallow sutures or small and low; spire surface smooth to sculptured (with evenly-spaced spiral ridges). A. inflata Shell inflated; body whorl flat-oval in cross section; keel high, truncate; spire with large with low spiral ridges, varible in expression; colorless to faintly yellowish or reddish-brown; circumglobal. <1.5 mm 4-1/2 a c
A. helicinoides Shell inflated: body whorl nearly circular in cross section; keel of low to moderate height, rounded; spire large with prominent spiral ridges, variable in expression; yellow or purple-violet; circumglobal. <2 mm 4-1/2 c c
A. californiensis Shell flattened; keel of moderate height, truncate, and with red-brown base; spire small (relative to shell size), low conical to globular, and smooth; colorless to uniformly or mottled, light yellow, brown or violet; North Pacific Ocean. <3.5 mm 3-1/4 a c
A. lesueuri group Shell spire extremely small; after metamorphosis a rapidly-expanding, single whorl (teleoconch) is formed (the adult shell consists of only 3-1/2 whorls). A. lesueuri Shell entirely transparent; spire low and conical with prominent (deep) sutures; keel high, truncate; circumglobal. <6 mm 2-1/2 b b
A. oligogyra Shell faint pink to yellow; spire low and rounded with shallow sutures: keel of moderate height, rounded; circumglobal. <3 mm 2-1/2 a b
A. peroni group Shell flat, of moderate to large size; spire small. A. peroni Spire low, rounded; keel of moderate height, truncate; shell colorless, becoming faintly yellow in large specimens; circumglobal. <10 mm 3-1/2 b b
A. fragilis Shell fragile (thin-walled), transparent and completely colorless; keel high; Atlantic Ocean. <9 mm 3-1/2 b b
A. rosea Spire nearly globular; spire whorls difficult to distinguish due to extremely shallow sutures of first two and one-half whorls; color faintly yellow; species name based on bright pink larval shell; circumglobal. <5 mm 3-1/2 b b
A. frontieri Spire low, with first and second whorls elevated, forming a low cone; distinctive thin, elevated spiral ridge along outer margin of spire whorls; keel of moderate height, rounded; colorless; Indian Ocean. <5.5 mm 4-1/2 b b
A. gaudichaudi group Shell flat; shell spire small, with low conical shape.
A. gaudichaudi Spire smooth; keel of moderate height, truncate and with a brown base; shell colorless; circumglobal. <3 mm 3-1/4 b b
A. plana Spire low conical with weak, spiral ridges; spire sutures violet; keel moderately low and rounded, with a brown base; Indo-Pacific. <3.5 mm 3-1/2 a b
A. selvagensisSpire very low conical, whorls with to without weak spiral ridges; spire sutures well defined, pink to light violet; keel base brown; eastern North Atlantic<1.5 mm3-3/4
a
b
A. echinogyra Spire low conical, slightly tilted relative to shell plane, with  prominent spiral ridges and secondary sculpture; spire reddish-brown and teleoconch colorless; Indo-Pacific. <2.5 mm 3-3/4 a c
A.inclinata group Shell spire large, globose (bee-hive shaped), strongly inclined relative to shell plane, with shallow sutures and numerous small tuberculae on the surface; keel moderately high and rounded; internal shell wall of radially-arranged lines. A. inclinata Spire with small tuberculae scattered on surface; spire weak rose color and last shell whorl colorless; circumglobal. <7 mm 4-1/2 b c
A. tokiokai Spire with spirally-arranged rows of low tuberculae; colorless to light yellow; circumglobal. <3 mm 5-1/2 b c
A. gibbosa group Shell spire large and high; internal shell wall without radially-arranged lines; shell completely transparent and colorless. A. gibbosa Spire moderately inclined relative to shell plane, with a broad base and pointed apex; circumglobal? (presence in Atlantic Ocean uncertain). <4 mm 6 b b
A. meteori Spire strongly inclined relative to shell plane, conical and steep sided; keel high, truncate; circumglobal. <4 mm 5-3/4 b b

*One species, Atlanta peresi, was described by Frontier (1966) from the western Indian Ocean. Although its adult shell morphology and opercular type were characterized by Frontier, its eye and radular morphologies are unknown. Subsequent studies of the atlantid heteropods from the Indian Ocean by Richter (1974) and Seapy et al. (2003) did not record the species, and the species' validity remains in question. The interested reader is referred to Richter and Seapy (1999) for a further description and discussion.

References

Frontier, S. 1966. Notes morphologiques sur les Atlanta récoltées dans le plancton de Nosy Bé (Madagascar). Cah. ORSTOM, Sér. Océanogr. 4: 131-139.

Richter, G. 1961. Die Radula der Atlantiden (Heteropoda, Prosobranchia) und ihre Bedeutung für die Systematik und Evolution der Famiie. Morphol. Ökol. Tiere 50: 163-238.

Richter, G. 1974. Die Heteropoden der "Meteor"-Expedition in den Indischen Ozean, 1964/65. "Meteor" Forsch.-Ergebnisse 17(D): 55-78.

Richter, G. and R. R. Seapy. 1999. Heteropoda, pp. 621-647. In: D. Boltovskoy (ed.), South Atlantic Zooplankton. Leiden: Backhuys Publ.

Seapy, R. R. 1990. The pelagic family Atlantidae (Gastropoda: Heteropoda) from Hawaiian waters: a taxonomic survey. Malacologia 32: 107-130.

Seapy, R. R., C. M. Lalli and F. E. Wells. 2003. Heteropoda from western Australian waters, pp. 513-546. In: F. E. Wells, D. I. Walker and D. S. Jones (eds.), The marine flora and fauna of Dampier, Western Australia. Perth: Western Australia Museum.

Title Illustrations
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Scientific Name Atlanta peroni
Location Hawaiian waters
Copyright © 2005
About This Page

Roger R. Seapy
California State University, Fullerton, California, USA

Correspondence regarding this page should be directed to Roger R. Seapy at

Citing this page:

Seapy, Roger R. . 2007. Atlanta. Version 12 April 2007 (under construction). http://tolweb.org/Atlanta/28752/2007.04.12 in The Tree of Life Web Project, http://tolweb.org/

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