ULTRASTRUCTURE OF THE CUTICLE OF LORICIFERA AND DEMONSTRATION OF CHITIN USING GOLD-LABELED WHEAT-GERM-AGGLUTININ

The pharyngeal and lorical cuticles of adult and larval Loricifera wer e investigated by transmission electron microscopy. LRWhite sections o f larval and adult Loricifera were labelled with the lectin wheat germ agglutinin (WGA) conjugated to colloidal gold. The pharyngeal cuticle of Nanaloricus mysticus exhibits a multilaminate epicuticle and an am orphous basal layer with osmiophilic fibres. The lorical cuticle consi sts of an osmiophilic or trilaminate epicuticle, one to three amorphou s layer(s), and a basal fibrous layer which is strongly labelled by th e lectin-gold conjugate. Chitinase treatment or competitive inhibition with N-, N'-, N ''-triacetylchitotriose exclude labelling almost comp letely, whereas competitive inhibition with N-acetyl-D-glucosamine doe s not affect labelling intensity. The binding of WGA in connection wit h competition experiments indicates the presence of chitin in the fibr ous layer. In most areas of a section, three amorphous layers extend b elow the epicuticle of the Nanaloricidae. Only in favourably orientate d sections can all three ''amorphous'' layers be seen to be formed by stacks of lamellae. Modified articulation sites with bundles of osmiop hilic longitudinal fibres and an osmiophilic plate (Nanaloricidae only ) occur in adult Loricifera, but not in the larval stages. The ultrast ructure of the lorical cuticle of the Loricifera resembles that of oth er Nemathelminthes (= Aschelminthes). The morphology of the articulati on sites and the number of lorical plates seem to differ between the L oricifera and Priapulida. Therefore, it is currently not possible to c onclude whether the lorica of the Loricifera and Priapulida are homolo gous structures. (C) 1997 The Royal Swedish Academy of Sciences. Publi shed by Elsevier Science Ltd.