It looks like my G. smithii. Chances are, it won't get much bigger than 4" at any rate. It should do okay in a 5 gallon tank minimum.
All it needs is a cycled tank with rock to explore and to make a home in. They only need to eat a couple or a few times per week. Mine eats thawed frozen krill from a straw. It also likes hermit crabs and snails.
More info here:
http://reefcentral.com/forums/forumd...?s=&forumid=37
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Cat exercise wheel