Monogena flatworm. Scanning electropn micrograph (SEM). Monogenea are small parasitic flatworms mainly found on skin or gills of fish. Monogena have adhesive organs called prophators and opishaptors. Prophators are a pair of adhesive structures which are found on either side of the mouth. The opishaptor is found at the posterior end (top) and is the more major organ of attachment having not only more well developed suckers, but also hooks or claws. Magnification: x35 when printed at 10 centimetres high.