ULTRASTRUCTURE OF THE RADULA APPARATUS IN SOME SPECIES OF APLACOPHORAN MOLLUSCS

Radula morphology, tooth formation and chitin localization areinvestigated in four genera of Solenogas-tres and one genusof Caudofoveata using transmission electron microscopy. Radulateeth are secreted by groups of odontoblasts in the radula sheath.Tooth shape is determined by the arrangement of the odontoblastsand preformed by microvilli. Chitin is produced in the odontoblastsand is present in the teeth as well as in the basal materialof Solenogastres and in the radula membrane of Caudofoveata.Because of its development pattern and its ultrastructural morphologythe basal material is confirmed as being identical with theradula membrane. Mitotic activity in the basal epithelium isthought to support the forward movement of the radula. (Received 18 April 1991; accepted 12 December 1991)