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Roger R. Seapy
Containing group: Carinarioidea


Atlantids are the most species-rich family of heteropods, containing over 60% of all species. They are small (< 1 cm), and their bodies can be retracted entirely into their shells and closed off by a chitinous operculum on the opercular lobe of the foot. The head has a pair of large tentacles anterior to the eyes. A large muscular sucker, located on the posteroventral margin of the swimming fin, is used to hold prey fast while feeding. Atlantids are found primarily between the surface and 200 m in tropical to subtropical waters. Many species undergo vertical migration from daytime depths into shallower waters at night.


A heteropod with:


  1. Shell
    1. Body fully retractable into shell.
    2. Adult shell with dextral (right-hand) coiling and laterally flattened.
    3. Shell aperture closed with operculum.
    4. Figure. Left - Side view of Atlanta helicinoides, with body retracted into shell, Hawaiian waters. Photograph copyright ? 2005 R. Seapy. Right - Frontal view of Atlanta plana shell with slight tilt, diameter 2.1 mm, Hawaiian waters. Scanning electron micrograph copyright ? 2005 R. Seapy.

  2. Foot
    1. Sucker large relative to fin size.
    2. Opercular lobe and operculum present.
    3. Figure. Side view of Oxygyrus keraudreni, Hawaiian waters. Operculum, located beneath opercular lobe in photograph, not visible. Photograph copyright ? 2005 R. Seapy.

  3. Head
    1. Tentacles large and may extend beyond contracted proboscis.
    2. Each eye elevated above head surface.
    3. Figure. Side view of head and proboscis of Atlanta peroni, Hawaiian waters. Photograph copyright ? 2005 R. Seapy.

  4. Radula
    1. Rachidian tooth (central tooth in each tooth row) with one (Atlanta and Protatlanta) or three (Oxygyrus) short cusps.
    2. Figure. Radula of Atlanta californiensis. Scanning electron micrograph copyright ? 2005 G. Richter.


Most species are in the genus Atlanta; Protatlanta and Oxygyrus are monotypic. Due to the variability in species-level characters in Atlanta, generic differences are few and difficult to use. The genera can be distinguished by the following characters:

Genus Shell and keel compositon Spiral portion of operculum
Atlanta Calcareous shell and keel Present
Protatlanta Calcareous shell and conchiolin* keel Present
Oxygyrus Conchiolin shell and keel Absent
* Conchiolin, especially in fresh specimens, can be recognized by its extreme transparency.


Batten, R. L. and M. P. Dumont. 1976. Shell ultrastructure of the Atlantidae (Heteropoda, Mesogastropoda) Oxygyrus and Protatlanta, with comments on Atlanta inclinata. Bull. Amer. Mus. Nat. Hist. 157: 263-310.

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.-Ergebn. (D), 17: 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.

Spoel, S. van der. 1976. Pseudothecosomata, Gymnosomata and Heteropoda (Gastropoda). Utrecht: Bohn, Scheltema & Holkema. 484 pp.

Spoel, S. van der, L. Newman and K. W. Estep. 1997. Pelagic molluscs of the world. World Biodiversity Data Base CD-ROM Series. Amsterdam: Expert Center for Taxonomic Identification (ETI).

Tokioka, T. 1961. The structure of the operculum of the species of Atlantidae (Gastropoda: Heteropoda) as a taxonomic criterion, with records of some pelagic molluscs in the North Pacific. Publ. Seto. Mar. Biol. Lab. 9: 267-332.

Title Illustrations
Scientific Name Atlanta peroni
Location Hawaiian waters
Copyright © 2005
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Roger R. Seapy

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

Citing this page:

Seapy, Roger R. . 2005. Atlantidae. Version 16 February 2005 (under construction). http://tolweb.org/Atlantidae/28732/2005.02.16 in The Tree of Life Web Project, http://tolweb.org/

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