Monogeneans: Monogenea

Monogeneans (mah-nuh-JEE-nee-uhns) are flatworm parasites that live mainly on fish skin and gills. Parasites (PAIR-uh-sites) are animals or plants that live on or in other animals or plants, or hosts, without helping them and usually harming them. Monogeneans have an organ at the rear of their bodies that holds hooks the worms use for attaching themselves to hosts. The organ holds large hooks, called anchors, and small hooks. Monogeneans live in only one host for their entire life cycle. Monogeneans are one–thirty-second to three-fourths of an inch (1 millimeter to 2 centimeters) long. Large monogeneans tend to be flat and leaf shaped, but the smaller worms are usually cylindrical. These flatworms are colorless and almost clear. When on fish skin some may be almost invisible to the human eye, either because they are clear or because they contain scattered coloring that matches the color of the host's skin. The digestive system of monogeneans consists of a muscular tube used to suck in food and a saclike or branched intestine with no anus (AY-nuhs). Monogeneans make both eggs and sperm.