The attachment of the ancyrocephalid monogenean Haliotrema balisticus to the gills of the trigger fish, Balistes capriscus (= carolinensis)

Abstract

Haliotrema balisticus attaches itself between the secondary gill lamellae of its host, Balistes caprisctis (= carolinensis), by means of a pair of ventral hamuli, which point ventrolaterally, and a pair of dorsal hamuli which point in a dorsal direction. The ventral hamuli, each of which pivots at the end of a ventral connecting bar, are operated by a pair of extrinsic muscles. The tendinous regions of these muscles pass through fibrous loops attached to the ventral hamuli and then join each other in the mid-line. Such an arrangement has a high mechanical advantage which may reduce the expenditure of energy required to maintain the hamuli in position in the gill tissue in the face of a strong gillventilating current and may also preserve the mobility of the free region of the body.The dorsal hamuli are not operated by the muscles and tendons associated with the ventral hamuli.Marginal hooklets and glands play subsidiary roles in attachment.I wish to express my thanks to Commander J. Parreira, Director of the Aquario Vasco da Gama in Lisbon, and to the Staff of the Aquario, in particular to Mr A. Ferreira, for their kind assistance and hospitality. I am also grateful to Dr Maria Monteiro and to Dr Maria Baptista. I am indebted to the Calouste Gulbenkian Foundation for a grant which made my visit to Portugal possible.