THE ULTRASTRUCTURE AND FUNCTIONAL-MORPHOLOGY OF A CAPTACULUM IN GRAPTACME CALAMUS (MOLLUSCA, SCAPHOPODA)

The structure and function of the captaculum in Graptacme calamus were studied using light microscopy, videomicrography, and transmission el ectron microscopy. Graptacme calamus utilizes a longitudinal ciliary b and to transport small food particles along the outstretched filament. The head of the captaculum, which bears the alveolar indentation, con tains a large ganglion, at least three types of gland cells, circular and longitudinal muscles, and connective tissue. It is likely that gla nd 1 secretes mucus which is used in the transport of food particles a nd that gland 2 secretes material which promotes adhesion of the alveo lus to the substratum. The function of gland 3 is unknown. Critical ob servation of the captaculum surface revealed that the cilia of the alv eolar region have truncated tips unlike those found on other regions o f the captaculum. These alveolar cilia probably aid in the distributio n of adhesive substance and in adhesion.