Ultrastructural observations on the hamuli of the monogenean gill parasite Cichlidogyrus halli typicus.

The ultrastructure of a monogenean hamulus is described for the first time. The ultrastructure of the dorsal and ventral hamuli of the monogenean gill parasite Cichlidogyrus halli typicus (Price & Kirk, 1967, 76: 137-144) Revue de Zoologie et de Botanique Africaines Paperna, 1979 (Annales du Musée Royal del'Afrique Centrale 226: 1-31) is similar but there are differences between different regions of a single hamulus. Each hamulus has three layers in the middle of the hook region, a thin outer layer, a middle layer forming the bulk of the hook and a central core made up of longitudinally oriented rods. The central core disappears in the distal region of the hook and the outer layer is absent in the proximal region of the hook. Both the shaft and the roots consist of two layers, the inner layer of the shaft is made up of longitudinally oriented parallel rods, and the corresponding layer of the roots being composed of long fibrils. The longitudinally orientated rods of the central core may provide inner strength to resist the physical strain on the hook and the outer, and possibly the middle layers, may provide chemical resistance to host's tissue secretion. The distal region of each root is covered with a fibrous hood, which appear to be a specialized region for binding muscle fibres to the sclerite.