Comparative ultrastructure of gastropod cephalic tentacles: Patellogastropoda, Neritaemorphi and Vetigastropoda

The fine structure of the cephalic tentacles of the three major basal gastr opod clades, Patellogastropoda (Docoglossa), Neritaemorphi, and Vetigastrop oda, is described based on transmission and scanning electron microscopy. T his was done to clarify cytological details and to provide data for functio nal considerations and for reconstructions of phylogenetic relationships. T he ultrastructural characteristics of the sensory elements, supporting cell s, and mucous cells of the cephalic tentacles differ considerably between t axa, whereas subepithelial cell types are remarkably uniform. The epithelium of neritaemorphs and vetigastropods is generally characteriz ed by ensheathing sensory cells forming ciliary tufts and by sunken, solita ry, vestigial cilia, which are probably characteristic of all supporting ce lls. Patellogastropoda show plesiomorphic ciliary features that also occur in Bivalvia and Solenogastres. Vetigastropoda usually have papillary tentac les. The Neritaemorphi may be divided into two groups based on the fine str ucture of supporting cells.