Gastrolecithus planus (Linton) (Cestoda, Tetraphyllidea) parasitizing Cetorhinus maximus (Gunnerus) (Elasmobranchii) from the North Sea

INTRODUCTION In 1889 Van Beneden described a new tetraphyllid cestode, Dinobothrium septaria, for which he erected a new genus. It was peculiar in having a rather small body with a very large scolex, the largest of all tapeworm holdfasts. Since then a small number of other species of Dinobothrium have been described (for two of them new genera were proposed, viz. Gastrolecithus Yamaguti, 1952 and Reesium Euzet, 1955). They have only been found in large sharks, both in preying and in plankton feeding species. Mola (1907) was the first investigator who found such a tapeworm in the Basking Shark, Cetorhinus maximus (Gunnerus). Euzet (1955) has tried to elucidate the remarkable and confused history of these animals. He recognized three genera and only three species, viz. Dinobothrium septaria van Beneden from Lamna nasus (Bonnaterre), Gastrolecithus planus (Linton) and Reesium paciferum (Sproston) both from Cetorhinus maximus (Gunnerus). Some incidental finds from other sharks have a doubtful status. The most remarkable fact is that these three species with similar scolices were placed in three different families: Dinobothrium septaria in the family Phyllobothriidae, Reesium paciferum in the family Prosobothriidae, while Euzet proposed a new family, Gastrolecithidae, for Gastrolecithus planus. However, it is the opinion of the present author that this view will not generally be accepted. It is improbable that the characteristic scolices would have evolved in three families. In the present paper Gastrolecithus planus is recorded from Cetorhinus maximus captured in the North Sea near the Dutch coast. Gastrolecithus planus (Linton, 1922)