Cardiapoda d'Orbigny 1836

Introduction

The genus Cardiapoda is similar in general body shape to Carinaria, but differs most conspicuously in lacking a macroscopic shell that covers the visceral nucleus; instead the shell is microscopic (only slightly larger than the larval shell) and is imbedded in the dorsal portion of the digestive gland in the visceral nucleus.  Both the right and left tentacles are well-developed and of equal size, unlike Carinaria (in which the right tentacle is greatly reduced or vestigial) and Pterosoma (where the right tentacle is absent). The cutis is thin, unlike the thick, gelatinous cutis in Carinaria and Pterosoma.

Brief Diagnosis

A carinariid genus with:

• Visceral nucleus exposed; not covered by a macroscopic shell
  
• Shell microscopic and imbedded in dorsal part of visceral nucleus
• Right and left tentacles well-developed and of equal size
  
• Tail ends either in a contractile fan-shaped expansion or a filamentous extension that can be greatly lengthened or shortened
  

Characteristics

1. Body morphology
   1. Visceral nucleus not covered by shell, as in Carinaria and Pterosoma
      
   2. Gills either numerous, forming a crest on the visceral nucleus, or few, located at the entrance to the mantle cavity
      
   3. Visceral nucleus stalk directed posteriorly
   4. Right and left tentacles of equal size and well developed
      

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      Figure. Frontal view of Cardiapoda richardi. © L. Madin

   5. Tail with a small dorsal crest that terminates either in a fan-shaped expansion that can be contracted or expanded (C. placenta) or a filamentous extension that can be greatly lengthened or shortened (C. richardi)
      

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      Figure. Lateral views of Cardiapoda placenta (left) with the terminal fan-shaped expansion and Cardiapoda richardi (right) with the low dorsal crest, elongate mid-ventral slit, and contracted reddish-brown filamentous tail extension. © R. Gilmer and © L. Madin, respectively.
      

   6. Cutis thin; in contrast with the thick, gelatinous cutis of Carinaria and Pterosoma
      

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      Figure. Swimming fin, head region and proboscis in Cardiapoda richardi. Note the folds in the thin cutis in the ventral part of the trunk and proboscis, resulting from ventral flexion of the proboscis. © L. Madin

2. Shell
   
   1. The adult shell is microscopic and consists of the protoconch (the larval shell following metamorphosis) and a rudimentary teleoconch. The teleoconch is produced at right angles to the shell aperture, forming an outwardly-radiating shelf
      
      

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      Figure. Drawings of the microscopic adult shell in Cardiapoda placenta, viewed from the right side and aperture (left and right, respectively). Shell diameter about 0.8 mm. Drawings modified from Tesch (1949) by addition of labels.

   2. Larval shell globular. Right side of shell with two spiral ridges on the second spire whorl. Left side of shell with umbilicus open and about 13 radiating ridges on umbilicus wall; aperture wide, slightly greater than 1/2 shell diameter
      

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      Figure. Scanning electron micrographs of the larval shell of Cardiapoda richardi, viewed from the right side, left side, and aperture.  Shell diameter = 0.6 mm. © R. Seapy

   3. With growth of the animal, the microscopic shell becomes imbedded in the digestive gland, with only the top of the protoconch visible
      

Comments

The genus Cardiapoda includes two species, which can be distinguished by the following characters:

References

Lalli, C. M. and R. W. Gilmer. 1989. Pelagic snails. The biology of holoplanktonic gastropod snails. Stanford University Press, Stanford. 259 pp.

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

Tesch, J. J. 1949. Heteropoda. Dana Report 34, 53 pp., 5 plates.