Ultrastructure of the early rostellum of Silurotaenia siluri (Batsch, 1786) (Cestoda: Proteocephalidae).

The neodermis of the whole early rostellum of Silurotaenia siluri (Batsch, 1786) bears filamentous microtriches. At the base, there are five to six irregular rows of hooks and spine-like microtriches. The rostellar hooks of S. siluri originate through the enlargement of microtriches. Electron-dense hook substance is deposited along the edges of the microthrix to form the hook blade and basal plate. The blade does not become hollow as in the cyclophyllidean cestodes. The basal plate of the hook, corresponding to the handle and the guard of Cyclophyllidea, is formed by the deposition of hook substance around the base of the microthrix. Within the centre of the base, only a narrow cleft-like core is occupied by distal cytoplasm. The hook bases are more deeply inserted into the distal cytoplasm, as the bases of the spine-like microtriches are localized on the rostellum below the rows of hooks. No hemidesmosomes, fixing the hook base to the basal lamina, are present. Eccrine gland cells and uniciliate and nonciliate sensory receptors of the primitive rostellum are described.