Canreef Aquatics Bulletin Board

my tank has been running for a year and a half now and today i came across three crabs that i definately didnt put in there. one was what ive heard called a box crab another i thought was one of the little crabs that are always on acros. until it started eating my acro. i caught and quarantined those two. unfortunately i couldnt catch the third. i know exactly what it looks like but i cant find a site to id it and i dont want to rip my tank apart if i can help it. anyone know of a site that list the different kinds of hitchhiker crabs.