Pseudanthocotyloides heterocotyle (van Beneden, 1871) Euzet & Prost, 1969 (Monogenea : Polyopisthocotylea : Mazocraeidae), a parasite of herring Clupea harengus L. and sprat Sprattus sprattus L. (Teleostei : Clupeidae)

A total of 690 herring Clupea harengus L. and 88 sprat Sprattus sprattus L. caught off the west coast of Sweden, in the North Sea and off the west and south coasts of the United Kingdom, were examined for gill parasites. The monogenean Pseudanthocotyloides heterocotyle (van Beneden, 1871) Euzet & Fr ost, 1969 was found in 38 (5.5%) herring and one (1.1%) sprat. The parasite was significantly (P < 0.05) more common off the west coast of Sweden than elsewhere and most specimens (62.5%) were found on the pseudobranchs. Only the smaller herring were infected. P. heterocotyle is redescribed and its taxonomy discussed, together with the possibility of host and parasite misi dentification in previous reports.