"Have you spotted any temnocephalans on your animals? They're pretty cute."This made me look twice and I found a couple looking very photogenic on the side of the first segment of the tail. Whipped out the camera and extension tubes and took this photo (which is fairly high magnification as you may be able to tell). Then I did a bit of research.
Temnocephalans (or Temnocephalids) are a type of flatworm (phylum Platyhelminthes), in the same class (Turbellaria) as things like Dugesia and Caenoplana. Unlike those 'roving' flatworms, Temnocephalans have a posterior sucker with which they anchor themselves, and a crown of tentacles (presumably for food capture?). As far as I know these guys don't do any harm to the crayfish they are found upon. Oh, and like Dugesia, you can see the eyespots of these critters giving them a cartoon-character appearance. To me, anyway.