I need help figuring out what is loose in my tank please. I have a fairly new Reef tank. I noticed tonight after the lights were off in the back corner of the tank a group of 3 or 4 translucient shrimp looking things. They were only about a 1/16th to an 1/8 of an inch in length but VERY fast when I tried to net one. They dont seem to venture far from the rock in that corner. As they only like the night, I cant get a picture to post. Any ideas would be helpfull.

I am concerned because also this evening I found one of my hermet crabs dead and without his shell, I FEAR I have a colony of mantis shrimp growing in my tank.

Thank you