ABSTRACT
Monogenea (Phylum Platyhelminthes) are common ectoparasitic flatworms of marine, brackish water and freshwater fishes. Together with parasitic Copepoda (Chapter 18), Monogenea are the most diverse assortment of ectoparasites of fishes. Monogeneans generally live on the external surfaces including the 'skin' or general body surfaces, fins, the head, gills, eyes and oral and branchial cavities. Some monogenean species parasitize internal sites with openings to the exterior such as the nasal tissue, urogenital system (including the cloaca and rectal gland) and sometimes the body cavity (Table 13.1). Exceptionally, a few species infect the digestive tract, heart musculature or blood vessels (Table 13.1; Whittington, 2005). Despite these exceptions, the Monogenea are widely referred to as ectoparasitic flukes of fish (e.g., Hayward, 2005;
Whittington, 2005) which distinguishes them from the Digenea that are principally endoparasitic or internal flukes (e.g., Cribb, 2005; Chapter 14).
