I included this image more for the narrative and the lesson than for the image itself. This is an Anchor Worm (Lernea species) that I removed from one of my Pond Comets. Unfortunately, when I removed it, I didn't realize that the worm's head remained attached inside the fish. I treated the wound with salt and formalin, but several days later the wound became infected and septicemia (blood poisoning) set in. Without its head I didn't recognize the worm as a Lernea species under the microscope. The inset shows what I should have seen.

Anchor Worms should be dabbed with turpentine, which causes the worm to release its hold. Then it can be removed safely with tweezers.