Last week we had the awful
tongue bug, so maybe it's fair to point out that many parasites are beneficial. In this case, the fish above allows the little shrimp into its mouth, because the shrimp collects and eats leftover crap from around the fish's teeth. The fish gets pearly whites, and the shrimp gets a meal and doesn't get et in return. Seems a fair deal. And it's a beautiful shot due to the colors.
(Don't like this one? I've posted
another set of IotD "B" images here.)