The Camelback Shrimp is recognizably different from the Peppermint Shrimp, in that it has a hump on its back. This shrimp isn't a good choice for reef tanks, but can be used to devour AEFW off infected corals, according to one site. Set up a hospital tank, place six of these shrimp in the tank, and place an infected coral in their midst for exactly 30 minutes, not a minute longer.
Feb 2014: I discovered this tiny hitchhiker in the rockwork. More than likely Tridacna hippopus sp., or Bear Claw clam.
Here's a pretty good view of what it looks like, if you happen to know the precise spot in my reef. It's tiny as can be.
Peppermint Shrimp - Lysmata wurdemanni -are often sought after because they tend to eat small aiptasia in the reef. While most LFS will carry these, some are possibly mistakenly sold as Peppermints when in fact they are Camelback shrimp. Camelbacks have a hump that is quite distinct when the animal is viewed from the side rather than from above (as pictured here). They do not harm most corals and fish tend to ignore them. They are usually only visible late at night with a flashlight, as they hide in the rockwork all day long.