The Ultrastructure and Functional Morphology of a Captaculum in Graptacme calamus(Mollusca,Scaphopoda)

The structure and function of the captaculum in Graptacme calamuswere studied using light microscopy, videomicrography, and transmission electron microscopy. Graptacme calamusutilizes a longitudinal ciliary band to transport small food particles along the outstretched filament. The head of the captaculum, which bears the alveolar indentation, contains a large ganglion, at least three types of gland cells, circular and longitudinal muscles, and connective tissue. It is likely that gland 1 secretes mucus which is used in the transport of food particles and that gland 2 secretes material which promotes adhesion of the alveolus to the substratum. The function of gland 3 is unknown. Critical observation of the captaculum surface revealed that the cilia of the alveolar region have truncated tips unlike those found on other regions of the captaculum. These alveolar cilia probably aid in the distribution of adhesive substance and in adhesion.