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Containing group: Atlanta

Introduction

Atlanta gaudichaudi is a small species (maximal shell diameter = 3 mm). Shell surface smooth and colorless, although the keel base is yellow-brown to brown. The shell spire consists of 3-1/4 to 3-1/2 whorls. Spire shape is low conical with a helicoid shape (due to rounded whorls and incised sutures). The keel is tall, with a truncate leading edge. The keel does not insert between the penultimate and last shell whorls. Eyes type b. Operculum type b. Radula type I, with unlimited numbers of tooth rows and monocuspid lateral teeth. This species differs from the other two in the A. gaudichaudi species group in that the shell spire lacks raised sculpture and the gyre of the operculum lacks spirally-arranged hooks or spines. The species has a cosmopolitan distribution.

Diagnosis

• Shell small; maximal diameter = 3 mm
• Shell colorless, with a smooth surface that lacks raised sculpture
• Spire low conical, with a helicoid shape that is due to rounded whorls and incised sutures
  
• Spire consists of 3-1/4 to 3-1/2 whorls
  
• Keel tall, with a yellow-brown to brown base and a truncate leading edge
  
• Keel does not insert between last two shell whorls
• Eyes type b
• Operculum type b
• Radula type I, with unlimited numbers of tooth rows and monocuspid lateral teeth
  

Characteristics

1. Shell
   1. Shell small; maximal diameter = 3 mm
   2. Shell colorless, except for a yellow-brown to brown keel base
   3. Shell surface smooth, lacking any sculpture on the spire
      
   4. Spire consists of 3-1/4 to 3-1/2 whorls
   5. Spire shape low conical with a helicoid shape, due to rounded whorls and incised sutures (see fifth SEM image and photograph of post-larval shell in apertural view below)
   6. Keel tall, with a truncate leading edge
      
   7. Keel does not insert between penultimate and last shell whorls
      
      

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      Figure. Shell of Atlanta gaudichaudi; right side (left) and spire (middle and right). Left and middle images modified from Richter (1974, fig. 8). Right image modified from Richter (1993, fig. 11). © 1974 and 1993 G. Richter
      

      

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

      
      

      Figure. Shell of Atlanta gaudichaudi; right side, tilted view (left) and close up  in apertural view (right). Images modified from Richter (1974, fig. 8) and Richter (1993, fig. 12), respectively. Scale bars = 0.5 mm (left) and 100 µm (right). © 1974 and 1993 G. Richter

   8. Larval shell with internal walls intact; not decalcified as in members of the A. inflata species group. Low conical spire with helicoid shape nicely illustrated in apertural view of larval and early post-larval shells (see below)
      
      

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      Figure. Dark field, transmitted light photograph of a post-larval shell of Atlanta gaudichaudi in apertural view. Image from Richter (1993, Fig. 13). © 1993 G. Richter

2. Eyes type b, with a transverse slit in distal pigmented tissue
3. Operculum type b (micro-oligogyre), lacking the spirally-arranged spines or hooks seen in the gyres of the other two species in the species group, A. plana and A. echinogyra
   
4. Radula type I
1. Number of tooth rows unlimited
2. No sexual dimorphism in radulae or radular teeth
   
3. Lateral teeth monocuspid
   
   

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   Figure. Sections of radulae from two large adult Atlanta gaudichaudi (shell sizes and sexes not known). Image modified by addition of scale bar from Richter (1993, Fig. 15). Scale bar = 50 µm. © 1993 G. Richter

Comments

Atlanta gaudichaudi can be easily distinguished from the other two members of the A. gaudichaudi species group by the absence of any surface sculpture on the shell spire and the lack of spirally-arranged spines (A. plana) or hooks (A. echinogyra) on the gyre of the operculum.

This species is most often confused with smaller A. peronii, which also has a smooth shell surface (lacking sculpture), comparable number of spire whorls, and the same eye, opercular and radular types (see the species summary table on the genus Atlanta page). However, the size and shape of the spire were reported by Richter (1993) to enable one to distinguish the two species. Richter noted that the spire of A. gaudichaudi is tall with a low conical, helicoid shape (described above), while that of A. peroni is very low conical (see the first two image pairs below). However, a comparison of the spire diameter in the two species (based on the two spire SEMs used here and the one from the A. peronii species page; see below) at three complete whorls indicates that at least for these examples the spire of A. gaudichaudi is not smaller than that of A. peronii, but rather appear to overlap in size.

The geographic distribution of Atlanta gaudichaudi is cosmopolitan in tropical to subtropical waters. However, in the Pacific Ocean its distribution is uneven. It has been recorded from Kuroshio Current waters off Japan (Tokioka, 1955; Okutani, 1957), eastern and northeastern Australian waters (Newman, 1990), and the Gulf of California (Seapy and Skoglund, 2001; O. Angulo, pers. comm.). However, despite the extensive sampling of Hawaiian waters (Seapy, 1990), it was never recorded there.

Other Names for Atlanta gaudichaudi Gray 1850

• Atlanta gaudichaudii Souleyet 1852

References

Okutani, T. 1957. Holoplanktonic Gastropoda in the "Kuroshio" Area, south of Honshu, May 1955. Records of Oceanographic Works in Japan, Special Number (New Series): 134-142.

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. 1993. Zur Kenntnis der Gattung Atlanta (V). Die Atlanta peroni-Gruppe und Atlanta gaudichaudi (Prosobranchia: Heteropoda). Archiv fur Molluskenkunde 122: 189-205.

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

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

Tokioka, T. Shells of Atlantidae (Heteropoda) collected by the Soyo-Maru in the southern waters of Japan. Publications of the Seto Marine Biological Laboratory 4(2-3): 237-250.