For my parasitic photo I could not resist putting up these. They are ghost shrimp, and the ghost shrimp on the top is a healthy female with eggs, while the pale one on the bottom is a female infected with Ione cornuta. The parasite is under the exoskeleton, but can be seen as a large lump on the side of the shrimp (right side).
This parasite goes through a rather complex life cycle, where if goes through a couple of different hosts before ending up in ghost shrimp. The first Ione to land on the shrimp's gills will become a female and the second one a male. They spend the rest of their lives in the shrimp's gill chamber, and grow with the shrimp.
While I seem to lack a photo of Ione outside of it's host, I do have a picture of a very closely related parasite Orthione, which looks and acts very much like Ione, save that it lives in mud shrimp instead of ghost shrimp.
(The little curled-up part towards the bottom left is the male, he is much smaller than the female and generally lives on her)