COMPARISON OF THE STRUCTURE OF THE PALLIAL TENTACLES OF SEVEN SPECIES OF SOUTH AFRICAN PATELLID LIMPET

The ultrastructure of the pallial tentacles of seven speciesof patellid limpet is described. The tip of most of the tentaclesexamined bears a crown of long cilia, whereas the shaft of thetentacles has small tufts (5–10 µm diameter) ofshorter cilia. Sections through the ciliated tufts show themto be composed of several cells, each bearing cilia. The ciliacontain 5–7 central microtubules and therefore do nothave the conventional 9 + 2 arrangement of microtubules. Nerveprocesses run from the base of each ciliated cell to a nervebundle in the centre of the tentacle, suggesting a sensory function.Estimates of densities of ciliated tufts suggest that the territoriallimpets (Patella cochlear and P. longicosta) have the greaternumber of tufts. Electron dense plate-like structures are foundin the centre of the pallial tentacles of Patella cochlear,P. longicosta, P. granularis, P. barbara and Helcion pruinosus.Each plate is about 0.2 µm wide and is surrounded by adouble membrane. It is suggested that these may play a rolein scattering or reflecting light and thus form part of thedermal light sensing ability of these animals. (Received 26 January 1987;