The attachment site, invasion route and larval development ofTrochopus pini, a monogenean from the gills ofTrigla hirundo

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Abstract
Adult specimens ofTrochopus piniattach themselves by folding the disk-shaped haptor around the edge of the host's primary gill lamella. They are able to move from one place to another with the aid of disk-shaped pads on the head region.Ducts from the posterior median gland cells, which are extensive in the head region of the adult, open on the periphery of each disk and exude an adhesive secretion.The oncomiracidium ofT. piniis described and evidence is offered in support of direct invasion of the gills by these free-swimming larvae. Special attention is paid to the development of the head region of the parasite. Newly attached larvae lose their eye lenses and possibly their anterior median gland cells; their lateral head glands are well developed and most probably serve for attachment of the head region, since the posterior median gland cells are poorly developed and appear to have no ducts. Later the posterior median gland cells and their ducts increase in numbers and, in association with the pads on the head region, take over from the lateral glands the job of attaching the head region.The paths of the tendons associated with the accessory sclerites on the haptor ofT. piniindicate that this gill parasite has evolved relatively recently from the ancestors of benedeniid skin parasites.I am most grateful to Commander J. Pareira, the Director of the Aquario Vasco da Gama in Lisbon where most of this work was done, and to the Staff of the Aquario and especially to Mr A. Ferreira. I am indebted to the Calouste Gulbenkian Foundation for a generous grant which made this visit possible. I am grateful also to the Directors and Staff of the Laboratoire Arago, Banyuls, France, the Station Biologique of the University of Bordeaux at Arcachon in France, and the Laboratory of the Marine Biological Association of the United Kingdom at Plymouth, England. I would like to thank the Royal Society for a grant from the Browne Fund which enabled me to work at Banyuls in 1962 and for a Pergamon Travel Award which made it possible to visit Arcachon in 1967.