Size differences in hamuli of Kuhnia scombri (Monogenea: Polyopisthocotylea) from different geographical areas not due to differences in host size

Hamuli of Kuhnia scombri from Scomber australasicus and S. japonicus from several localities in the Pacific Ocean show marked differences in length. Hamuli from large fish are slightly longer than those from small fish caught in the same geographical area (northern New Zealand). Differences correlated with host size are much less than those associated with geographical area and may be due to infections acquired in different localities. Taxonomic studies of Monogenea must take geographical variation and, to a lesser degree and in at least some species, effects of host size into consideration.