Class Monogenea
This class of Pltyhelminthes only has one generation in their life cycles hence the name, they're external parasites on fresh water and marine fishes mostly. Monogeneans feed on the epithelial tissue , blood , or mucus of these animals. Adults release eggs that have sticky threads attached to them to stick to the gills of the fish. Oncomiracidium hatch from the eggs and swim to another fish to feed off of until adulthood.