Cardiapoda placenta (Lesson 1830)

Introduction

Cardiapoda placenta is the larger of the two species of Cardiapoda, achieving a maximal size of about 110 mm. Features that distinguish C. placenta from C. richardi include: numerous gills (>20) that form a median crest on the visceral nucleus, fin sucker in both males and females, a tail that terminates in 12 finger-like extensions that can be expanded and contracted, and a narrowly triangular eye shape.

Brief Diagnosis

A species of Cardiapoda with:

• Gills numerous (>20), forming a median crest on the visceral nucleus
• Fin sucker present in both sexes
  
• Tail terminates in 12 finger-like contractile extensions
• Shape of eye, viewed dorsally, narrowly triangular
  

Characteristics

1. Body morphology
   
   1. Gills numerous (>20), forming an arc or crest on the posterior and dorsal surface of the visceral nucleus (see title illustration)
      
   2. Fin sucker present on both males and females
      
   3. Tail terminates in 12 fan-shaped, reddish-brown finger-like extensions that are normally expanded (see below left), but which are contracted when the animal is disturbed (see below right)
      
      

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      Figure. Cardiapoda placenta in side view (left), to illusrate the expanded terminal tail extensions. © R. Gilmer. Photograph on right of C. placenta with contracted reddish-brown tail extensions. © A. Connell
      

2. Shell
   1. Adult shell microscopic; teleoconch formed at right angles from shell aperture of larval shell
      
      

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      Figure. Adult shell of Cardiapoda placenta, viewed from the right side and aperture (left and right images, respectively). Note the broad teleoconch, suggesting that this shell was taken from a mature adult, in contrast with the shell with a small teleocondh that was illustrated by Tesch (1949) and was used here on the Cardiapoda page. © 1976 S. van der Spoel

   2. Larval shell of C. placenta similar to that of C. richardi, but the outermost of the two spiral ridges (or striae) on the second whorl of the spire is much shorter in C. placenta than in C. richardi (see SEM on C. richardi page). The interested reader is referred to the scanning electron micrographs of the larval shells of the two species of Cardiapoda from the North Atlantic Ocean in Thiriot-Quiévreux (1975)
      

Comments

In-situ field observations of C. placenta by Ronald Gilmer (reported in Lalli and Gilmer, 1989) revealed that both sexes are brightly colored with reddish-brown spots covering the body, although the number and brightness of these spots are greater in females. The pigment spots were seen to be highly contractile, changing rapidly from 0.5 to 2 mm in diameter. Also, the terminal finger-like expansions on the tail varied from reddish-brown to black, and flashed during prey capture.

The feeding behavior of C. placenta was observed on 38 occasions by SCUBA divers in the Sargasso Sea and Florida Current (Hamner, et al., 1975). The most frequently encountered prey were salps. Attack of a prey item was seen once in the field and twice in aquaria (using hand-collected animals). In each case the prey's silhouette appeared to have been located visually from beneath by the upward-searching predators from as far away as 60 cm. In each case, the predator swam rapidly (up to 40 cm/sec) up to the prey and captured it with the buccal cones, followed by ingestion (taking about 10 min) using the radula and peristaltic movements of the proboscis.

References

Hamner, W. M., L. P. Madin, A. L. Alldredge, R. W. Gilmer, and P. P. Hamner. 1975. Underwater observations of gelatinous zooplankton: Sampling problems, feeding biology, and behavior. Limnology and Oceanography 20: 907-916.

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

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

Thiriot-Qui?vreux, C. 1975. Observations sur les larves et les adulte de Carinariidae (Mollusca: Heteropod) de l'Oc?an Atlantique Nord. Marine Biology 32: 379-388.