INTERSEXUALITY IN THE CRUSTACEAN GAMMARUS-DUEBENI

We describe the external and internal morphology of intersex Gammarus duebeni from Budle Bay, Northumberland and present the first scanning electron micrograph of the external morphology of an intersex. The pattern of intersex expression in this population differs from that previously described in a German population: intersexes are more frequent in the UK population; and all conform to the intermediate form of the intersex types described in the German population. Such a contrast between populations has not previously been described and may provide a tool to understand the phenomenon. The distribution of a feminizing microsporidian is examined. However, parasitism is not the main agent of intersexuality.