Complete

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Containing group: Atlanta

Introduction

The maximal shell size of Atlanta lesueurii appears to vary geographically (from 2 mm in Hawaiian and eastern Australian waters to 6 mm in the tropical western Pacific). The shell is transparent, thin and fragile, with a smooth surface (lacking raised sculpture). The spire is very small, somewhat elevated and compact, consisting of about 2-1/2 whorls. Spire  sutures are deep, with the result that the whorls can be easily distinguished. After metamorphosis the outermost whorl enlarges and inflates rapidly and the keel becomes progressively taller, becoming very tall in large adults and having a truncate leading edge. The keel base and spire sutures are colorless. Eyes type b, with a large lens. Operculum type b. Radula type I, with a triangular shape; largest in the genus Atlanta. Geographic distribution is cosmopolitan in tropical to subtropical waters. Vertical distribution in Hawaiian waters restricted to upper 150 m, with most individuals in the upper 100 m and some evidence for nocturnal migration into the upper 50 m.

Diagnosis

• Maximal shell size appears to vary geographically, between 2 and 6 mm
  
• Shell transparent with a thin, fragile walls
• Shell surface smooth; lacking surface sculpture
• Spire compact, comprised of about 2-1/2 whorls
• Spire sutures incised, enabling distinction of whorls
• Keel tall, with a truncate leading edge
• Eyes type b; lens large
  
• Operculum type b
• Radula type I, triangular shape; largest radula in the genus

Characteristics

1. Shell
   1. Maximal shell size appears to vary geographically (=6 mm in the western tropical Pacific [Souleyet, 1852], 4 mm in the North Atlantic and Indian Oceans [Richter, 1986, 1974] and 2 mm off Hawaii [Seapy, 1990b] and eastern Australia [Newman, 1990]).
   2. Shell transparent with thin walls and keel
   3. Shell surface smooth, lacking any raised sculpture on the spire whorls
      
   4. Spire very small, compact and somewhat elevated, consisting of about 2-1/2 whorls; spire whorls distinct due to deep sutures (see tilted view of spire below)
      
   5. Keel tall, with a truncate leading edge
      
      

      Click on an image to view larger version & data in a new window

      
      

      Figure. Scanning electron micrographs of a 1.2 mm Atlanta lesueurii, viewed from the right side (upper left), the shell spire (upper right), the right side tilted (lower left), and the spire tilted (lower right). Scale bars = 0.5 mm (upper and lower left) and 100 µm (upper and lower right). ©

2. Coloration: in Hawaiian waters juveniles lack body coloration (see second title illustration), but with growth the spire tissues take on pink (see first title illustration) to pinkish-violet (see photograph below) coloration
   
   

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   Figure. Specimen of a male Atlanta lesueurii retracted into its shell. Note the pinkish-violet  coloration of the spire tissues. Shell diameter = 1.5 mm. ©

3. Eyes type b, with a large lens (see first title illustration; also, in enlarged view the transverse slit in the distal pigmented tissue of the right eye can be discerned)
4. Operculum type b; thin
5. Radula type I; largest in the genus Atlanta
   1. Shape triangular
   2. Lateral teeth monocuspid (Richter, 1961)
      
   3. Number of tooth rows can exceed 100 in older adults (Richter and Seapy, 1999)
      

Other Names for Atlanta lesueurii Gray 1850

• Atlanta lesueuri Souleyet 1852

References

Newman, L. J. 1990. The heteropod fauna (Prosobranchia, Heteropoda) of Australian and Papua New Guinean waters: a taxonomic and distributional review. Ph.D. thesis, University of Queensland, Australia.

Richter, G. 1961. Die Radula der Atlantiden (Heteropoda, Prosobranchia) und ihre Bedeutung f?r die Systematik und Evolution der Famiie. Zeitschrift f?r Morphologie und ?kologie das Tiere 50: 163-238.

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. 1986. Zur Kenntnis der Gattung Atlanta (II). Atlanta lesueuri Souleyet und Atlanta oligogyra Tesch (Prosobranchia: Heteropoda). Archiv f?r Mollusken-kunde 117: 19-31.

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 faunistic survey. Malacologia 32(1): 107-130.

Souleyet, [L. F. A.]. In: Eydoux, [F.] and Souleyet [L. F. A.], 1852. Voyage autour du monde execute pendant les annees 1836 et 1837 sur la corvette 'La Bonite'... Zoologie, col. 2. 664 pp. A. Bertrand, Paris.