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. Radula with a central, or rachidian, tooth shape typical of other carinariids, with three medial, pointed cusps and small lateral processes
   
   

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

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

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      Figure. Adult shells 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 broad teleoconch, arising at right angles and outward from the aperture of the coiled protoconch. 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 arc of gills and the location of the imbedded shell are  indicated in the photograph. Photograph modified from Thiriot-Quiévreux (1975, Fig. 4C) © 1975 C. Thiriot

   3. Larval shell globular, with a large oval aperture (A and B, below). The spire (C, below) has two spiral ridges on the second whorl. In C. placenta the outermost of these ridges is shorter than that in C. richardi (see SEM 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. 4C) © 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: 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.