Light micrograph of a Trematoda flatworm, Polystoma genus. This species is parasitic in the bladder, nasal cavities, mouth, pharynx or esophagus of amphibians and reptiles. Note mouth with oral sucker, posterior organ with suckers and hooks, intestine, testis, ovary and other organs. Trematoda, or Flukes, are external or internal parasites of man, fish and mollusks, often all three by the same species in a complicated life history, and most other vertebrates. Magnification x11 at 6x7 cm.