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
      
   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, but can contract when the animal is disturbed
      
      

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      Figure. Left: black and white, in-situ photograph of Cardiapoda placenta, left side of body; note the fan-shaped, ventral tail extensions. © R. Gilmer. Right: Photograph of posterior portion of C. placenta, left side of body; note that the tail extensions are retracted. © A. Connell
      

2. Radula with a tricuspid central (rachidian) tooth. The cusps are pointed, comparable in length, and the lateral cusps angle outward somewhat from the median cusp. This tooth shape differs from that in C. richardi in that the lateral cusps are shorter than the median cusp and the lateral cusps do not angle outward.
   
   

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   Figure. Radula of Cardiapoda placenta. Left: Lower magnification view; proceeding inward in each tooth row, the photograph shows the terminal parts of the elongate paired marginal teeth, the elongate lateral tooth, and the central rachidian tooth. Right: high magnification view of three central rachidian teeth. Photograph from Thiriot-Quiévreux (1975, Fig. 5A,B) © 1975 C. Thiriot

3. Shell
   1. Adult shell microscopic; following metamorphosis teleoconch is formed at right angles from aperture of protoconch (larval shell)
      
      

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      Figure. Adult shell of Cardiapoda placenta. Left: sketches of shell, viewed from the right side and aperture, respectively. Right: Scanning electron micrograph of shell, viewed from frontal. Note in both images the large size of the teleoconch in contrast with the early adult shell used on the Cardiapoda page (drawn by Tesch,  1949). Shell sketches © 1976 S. van der Spoel; SEM photograph © Orso Angulo

   2. In adult animals, the shell is located at the posterior end of the visceral nucleus, beneath (ventral to) the most posterior gills.
      
      

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      Figure. Posterior portion of the stalked visceral nucleus in Cardiapoda placenta. The posterior portion of the dorsal gills and the postero-ventral location of the imbedded shell are indicated in the photograph. Photograph modified from Thiriot-Quiévreux (1975, Fig. 4B) © 1975 C. Thiriot

4. Larva
   1. Larval body light brown to clear; digestive gland yellow; velum bordered by brown pigment, with two large brown patches on each lobe (Thiriot-Quiévreux, 1975)
   2. Larval shell globular, with a large oval aperture (below left). The spire has two spiral ridges on the second whorl (below right). In C. placenta the outermost of these ridges is shorter than that in C. richardi (see larval shell on C. richardi page).
      
      

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      Figure. Larval shell of Cardiapoda placenta viewed from the right side, tilted (left) and spire (right). Photographs modified from Thiriot-Quiévreux (1975, Fig. 1F,G) © 1975 C. Thiriot

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 University Press, Stanford. 259 pp.

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

Thiriot-Quiévreux, C. 1975. Observations sur les larves et les adultes de Carinariidae (Mollusca: Heteropoda) de l'Océan Atlantique Nord. Marine Biology 32: 379-388.