This was posted by thomas712:
I'm familier with this problem. Been asking about it for years, everytime someone mentions the Black Spot problem with cleaner shrimp. Finally it was Bang Guy who id-it for me.
It is an Epicaridean isopod. This is a parasite that shows up as an irregularly formed black mass in the abdominal region of the shrimp. So far I'm guessing that about 95% of the shrimp that are found to have this parisite wind up dead.
You may find that when your shrimp molts that these black spots dissapear, but in many that I have spoken to they wind up comming back, the parisite does not go away.