Microhabitat segregation on a gill arch (B) in respect to host specificity (A). (A) Congeneric monogenean species “A” and “B” are host-specific for a fish species “a”. Congeneric monogenean species “C” and “D” are generalists with different host ranges, i.e., species C infects three fish species (“a”, “b” and “c”) and species D infects two fish species (“a” and “c”). (B) Microhabitat position of four congeneric monogenean species parasitizing a fish species “a” on the gill arch. While two host-specific monogenean species (in light and dark green) for a fish “a” occupied closely related microhabitat positions within fish species “a”, two generalist species (in orange and red) infecting a wide range of fish species occupied distant microhabitat positions on the gill arch of fish species “a”.