The adhesive mechanism of the monogenean parasite Tetraonchus monenteron from the gills of the pike (Esox lucius)

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Abstract
The monogenean parasite Tetraonchus monenteron attaches itself to the gills of the pike (Esoz lucius) by means of two pairs of large hooks (= hamuli). One pair of hooks is directed ventrally and the outer (flanking) pair is directed dorsally so that the hooks impale two adjacent secondary gill lamellage. Each lateral pair of hooks (one ventral and one dorsal hook) is operated by a single extrinsic muscle, the tendinous region of which is threaded through two fibrous loops (= Pulleys), one attached to each hook. Each tendon on entering the haptor also passes beneath transverse fibres joining the anterior ends of the two ventral hooks and these fibres probably act as a third pulley. This complex pulley system has a high mechanical advantage so that the energy used by the parasite to hold its hooks in position against the strong gill ventilating current of the host is minimal.The mechanics of the adheasive apparatus of T. monenteron are compared with those of the monogenean gill parasite Amphibdelloides maccallumi, in, which the pulley system is less complex.I would like to express my thanks to Mr G. W. Vane who kindly caught some pike for me, and to Dr P. C. Croghan and Mr S. A. Hodson for helpful discussion on the mechanical aspects of the adhesive apparatus.