An ultrastructural study of the haptor of the microbothriid monogenean Leptocotyle minor from the skin of the dogfish Scyliorhinus canicula (Scyliorhinidae)

The microbothriid monogenean Leptocotyle minor attaches itself by means of cement to a single denticle of its host, the dogfish Scyliorhinus canicula (Scyliorhinidae). This cement is produced by fusion of large numbers of ovoid secretory bodies of a single type, characterised by the presence of several electron-lucent spherical subunits within the electrondense matrix of each secretory body. These bodies are produced by tegumentary cytons near the haptor and conveyed via internuncial processes to a highly specialised microvillous adhesive tegumental layer lining the saucer-shaped haptor. The bodies are discharged from this adhesive tegument, probably by exocytosis, via the apical membrane between the microvilli. A unique feature of the adhesive tegument is the presence of electron-dense striated columns spanning the narrow tegumental layer. Apically these columns have extensions, which enter one or more microvilli and become incorporated into their substructure. Basally the columns broaden and abut correspondingly broad columns of lower electrondensity derived from the interstitial sub-tegumentary material.