THE FINE STRUCTURE OF THE CTENIDIAL SENSE ORGANS (BURSICLES) OF VETIGASTROPODA (ZEUGOBRANCHIA, TROCHOIDEA) AND THEIR FUNCTIONAL AND PHYLOGENETIC SIGNIFICANCE

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Abstract
The fine-structure of the bursicles of members of all three subgroups of Vetigastropoda (Fissurelloidea, Pleurotomarioidea, Trochoidea) is described. Specific sensory elements (paddle cilia) suggest a chemosensory function of the sense organs. This agrees with earlier physiological results which demonstrated the role of bursicles in detecting predatory sea-stars. Similar pockets in the (secondary) gill-leaflets of the Pseudococculinidae, are not homologous with the bursicles. The lack of bursicles in group-B hot-vent limpets and in Neomphalus excludes these groups from the Vetigastropoda. The bursicles are regarded as a synapomorphic character of the vetigastropod groups proving their evolutionary unity.