I found a worm in my aquarium yesterday. It was a white worm with a red center running from end to end, and they were from microscopic to about 1 cm long . The water was about 68 degrees, and I found them while treating for an ich infection. I sucked some up with an eyedropper to examine under a microscope, and found that the worm had a straw-like mouthpart, and many hairs around it. The aquarium was later vacuumed, so that removed many of the worms. If anyone knows what this is, or at least knows whether or not this is a harmful parasite, please let me know.

I took some pictures of it, in actual size, and through the microscope.

Actual size: Aquarium Gallery - Mystery Worm (Parasite?)

Under the microscope (40x): Aquarium Gallery - Mystery Worm (Parasite?)

Head (100x): Aquarium Gallery - Mystery Worm (Parasite?)

Tail (100x): Aquarium Gallery - Mystery Worm (Parasite?)