Ultrastructure of the pharyngeal cuticle and lectin labelling with wheat germ agglutinin-gold conjugate indicating chitin in the pharyngeal cuticle of Oesophagostomum dentatum (Strongylida, Nematoda)

The ultrastructure of the pharynx of the first juvenile stage and of adult Oesophagostomum dentatum (Nematoda, Strongylida) is investigated by TEM. Additional light microscopical and SEM data are presented for the anterior alimentary canal of all life-history stages and for adult O. quadrispinulatum. Ultrathin sections of adult and the first juvenile stage O. dentatum are labelled with the lectin wheat germ agglutinin coupled to colloidal gold. The pharyngeal cuticle consists of a trilaminate epicuticle and an amorphous basal layer, which also exhibits individual fibres in adult worms. The pharyngeal cells of the first juvenile stage an already arranged as in the adult worm. In comparison with data for additional nematodes taken from the literature, a trilaminate epicuticle and an amorphous basal layer are postulated for the pharynx in the ground pattern of the Nematoda. Lectin-gold labelling reveals a strong binding to the pharyngeal cuticle of O. dentatum. Competitive inhibition experiments with N-acetyl-D-glucosamine and triacetylchitotriose, as well as treatment with chitinase, neuraminidase and sulphuric acid, indicate that the pharyngeal cuticle contains chitin. This finding is supported by staining of the pharyngeal cuticle by the fluorescent brightener calcofluor white in cryosections of O. dentatum. The occurrence of chitin is interpreted as an original character of the Nematoda. (C) 1997 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd.