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Atlanta plana Richter 1972

Roger R. Seapy
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Containing group: Atlanta

Introduction

Atlanta plana is a moderately small species (maximal shell diameter = 4 mm). The shell is colorless except for the yellow-brown to red-brown keel base and violet spire sutures. The spire consists of 3-1/2 whorls and has a low, conical shape with rounded whorls and incised sutures. The spire bears two low spiral ridges on the second and third whorls. On the second half of the third whorl the spiral ridges are replaced by small punctae. The keel is moderately low with a rounded profile. Keel inserts between last two whorls in shells larger than about 3 mm. Eyes type b. Operculum type b., with a gyre that bears an outwardly-directed spiral row of narrow, low spines. Radula type I, with unlimited numbers of tooth rows and no sexual dimorphism. Geographic distribution Indo-Pacific. Vertical distribution in Hawaiian waters mostly limited to the upper 150 m, with limited migration of individuals into the upper 45 m at night.

Diagnosis

Characteristics

  1. Shell
    1. Shell moderately small; diameter to about 4 mm
    2. Spire small, consisting of 3-1/2 whorls
    3. Spire shape low conical, with rounded whorls and incised sutures
    4. Spire sutures violet (see title illustration)
    5. Two low spiral ridges present on the second and third spire whorls. In the last half of the third whorl, the ridges break up and are replaced by spiral  rows of small, low punctae.
    6. Keel somewhat low and rounded in profile, inserting between the penultimate and the last shell whorls in shells larger than about 3 whorls
    7. Keel base yellow-brown to red-brown
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      Click on an image to view larger version & data in a new window

      Figure. Shell of Atlanta plana viewed from the right side (left) and the spire (right). Scale bars = 0.5 mm (left) and 100 um (right). ©


      Figure. Shell of Atlanta plana in tilted view from the right side (left) and the spire (right). Scale bars = 0.5 mm (left) and 100 µm (right). ©

    8. Larval shell with a low conical spire, composed of rounded whorls and incised sutures (see second image below). Two spiral ridges are present on the second whorl and extend onto the third whorl. A raised, thin spiral ridge is located  on the outer edge of the shell whorls, begining at the same point as the spiral ridges on the second whorl and continuing to the shell aperture (see first image below)
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      Click on an image to view larger version & data in a new window

      Figure. Larval shell of Atlanta plana, viewed from the right side (left) and the right side at about a 60° tilt (right). Scale bars = 100 µm. ©

  2. Eyes type a, without a transverse slit in the distal pigmented tissue
  3. Operculum type b (micro-oligogyre)
    1. Gyre portion of operculum distinctive, bearing narrow, flattened and outwardly-directed spines
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      Figure. Operculum of Atlanta plana; whole operculum (left) and close up of gyre region, with spiral row of outwardly-directed spines. Scale bars = 100 µm (left) and 50 µm (right). ©

  4. Radula type I
    1. Number of tooth rows unlimited
    2. No sexual dimorphism in teeth or in radula size or shape
      Click on an image to view larger version & data in a new window
      Click on an image to view larger version & data in a new window

      Figure. Radula of Atlanta plana; section of radula (left) and close up of two central teeth. Images from Richter (1987, figs. 48 and 56), modified by addition of scale bars. Scale bars = 100 µm (left) and 25 µm (right). © 1987 G. Richter

Comments

The shells of Atlanta plana and A. gaudichaudi are very similar in appearance (discussed by Richter, 1974 and Seapy, 1990a). Both species are moderately small (maximal shell diameters of 3 and 4 mm, respectively) and have spires composed of about the same number of whorls (about 3-1/2). The spires in both species have a low conical shape with incised sutures. The shells differ most conspicuously in the presence and absence, respectively, of spiral sculpture on the second and third spire whorls. Their soft part morphologies also differ; the eye types are different (a and b, respectively), and the opercular gyres either possess (A. plana) or lack (A. gaudichaudi) spines.

Atlanta plana can be an abundant species in Hawaiian waters (Seapy, 1990a,b and 2008), with the result that it is well suited for quantitative ecological studies. Diel patterns of vertical distribution of heteropods were examined based on replicated, opening-closing net samples (Seapy, 1990b). Atlanta plana ranged downward to 200 m during the day, although it was only abundant in waters shallower than 90 m. At night there was a pronounced upward migration from a 45-90 m depth interval into the upper 45 m. In a 2008 study based on duplicated opening-closing MOCNESS samples, the species ranged downward maximally to a 160-200 m depth interval at a station 5 nmi off the coast (comparable in location to the area sampled in the 1990b study). Similar to the earlier findings, densities were higher in the upper 40 m during the night than the day, although the differences were far less striking. Onshore-offshore comparisons of abundance patterns were markedly different between fall and spring sampling periods; maximal numbers were recorded at a station 5 nmi offshore in the fall, while in the spring abundances decreased shoreward by three-fold from a maximum at a 15 nmi station to a minimum at a 1 nmi station. 

References

Richter, G. 1974. Die Heteropoden der "Meteor" Expedition in den Indischen Ozean 1964/65. "Meteor" Forschungs-Ergibnisse Ser. D, No. 17, pp. 55-78.

Richter, G. 1987. Zur Kenntnis der Gattung Atlanta (III), Atlanta inflata, A. helicinoides, A. echinogyra und A. plana (Prosobranchia: Heteropoda). Archiv fur Mollusken-Kunde 117: 177-201.

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

Seapy, R. R. 1990b. Patterns of vertical distribution in epipelagic heteropod molluscs off Hawaii. Marine Ecology Progress Series 60: 235-246.

Seapy, R. R. 2008. Offshore-inshore and vertical distributional patterns of heteropod mollusks off leeward Oahu, Hawaii. Marine Biology 154: 985-995.

Title Illustrations
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Scientific Name Atlanta plana
Location Hawaiian waters
Specimen Condition Live Specimen
Sex Female
Life Cycle Stage adult
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About This Page


California State University, Fullerton, California, USA

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

Page: Tree of Life Atlanta plana Richter 1972. Authored by Roger R. Seapy. The TEXT of this page is licensed under the Creative Commons Attribution License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

Citing this page:

Seapy, Roger R. 2010. Atlanta plana Richter 1972. Version 21 March 2010 (under construction). http://tolweb.org/Atlanta_plana/28770/2010.03.21 in The Tree of Life Web Project, http://tolweb.org/

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