Possible Parasites?

Question
QUESTION: We have a 12 gallon nano aquarium with hermits, 1 emerald crab, 1 shrimp, snails and 5 small corals.  We have no fish yet because our store had limited supply when we went to buy.  There are what seems to be small snails on rocks/back of the tank.  They move MUCH faster than snails and are barely visible.  Not sure if these are good for us or if we should try and get rid of them.  Thanks

ANSWER: I am sorry Darin but in order for me help you identify these creatures I am going to need some kind of description. Are they snails with a shell on their backs or are they flat and no shell? What color are they? Size? Do they come out more at night or during the day. Some possibilities are snails, flatworms, seaslugs, amphipods, copepods, or isopods. If you can get back to me with some more description I am sure I will be able to help you identify these unknown creatures!

---------- FOLLOW-UP ----------

QUESTION: So I looked more closely at the little critters.  They at first look like snails, but on further looking, they have legs.  They don't look like shrimps/crabs, but could be because they are so small.  They are all white/light colored and VERY small.  They are out most of the time but most easily observed with the lights on.  They are primarily located on the back wall (most algae growth) and a few rocks in the aquarium.  I have observed the emerald crab grabbing one and eating it, but no other crabs/shrimp eating have happened.  Hope this helps you more.

Answer
Ahh! Much better description! Do they look like tiny white bugs crawling around in your tank? What you are most likely seeing are simply a healthy population of copepods in your tank. This is a sign that your tank is doing great and is supporting the kind of life that is one of the building blocks of life in the ocean. Here is a website that can tell you all you may want to now about copepods(and probably some things you could care less about). These creatures are very good for your tank as they will eat any uneaten food particles, fish poop, algae, and any other thing that can build up and pollute your tank. They are also a good food source for your corals and fish(when you get some).

http://www.luciopesce.net/copepods/intro.htm