The life cycle of the monogenean Entobdella soleae, a skin parasite of the common sole

Abstract

The life cycle of Entobdella soleae, a monogenean skin-parasite of a marine bottom-living flatfish (Solea solea) has been described and related to the habits of the host, which buries itself in the sediment for some time each day and when not buried rarely moves more than a few centimetres from the sea bottom.The eggs of the parasite are laid by specimens attached to the lower surface of the host and are anchored to sand grains on the sea bottom by an egg stalk bearing sticky droplets. The anchoring device may prevent the eggs from being carried by water currents vertically or laterally out of the region inhabited by soles.The free-swimming oncomiracidium which hatches from the egg invades the anterior part of the upper surface of the fish, which is the only part exposed when the fish is buried in the sand. After a short period of development on the upper surface the parasite emigrates to the lower surface where sexual maturity is reached.Adult parasites, which are distributed randomly on the lower surface, are orientated with the adhesive organ upstream with respect to water currents produced by the forward locomotion of the host, but the parasites are capable of moving from place to place on the lower surface of the fish. This movement of the parasite may be connected with the nature of the food.I wish to thank the Director and Staff of the Plymouth Laboratory and in particular Mr J. E. Green, for invaluable assistance. I am also very grateful to Dr J. Llewellyn for advice and criticism. The work was conducted during the tenure of a Fishery Research Training Grant from the Development Commission.