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[fkshiu]

Everything that comes with live rock has its place in a reef ecosystem. The majority of the time it is something useful to the aquarist - even the really ugly ones. It was probably some kind of detrivore, but it's impossible to know now that you've killed it. The next time you see a hitchhiker perhaps you should consider isolating it and taking a picture before going "eeek!" and stomping on it.