[Rob]

What was an Arrow Crab doing in my reef tank anyway?

Placed there by well-meaning relative while I was on vacation six months ago, after some "expert" in a pet store advised him that it was "reef-safe". Now you know why I dislike even the term, "reef-safe".

How did I catch the sod? (the crab I mean, not the relative)

It somehow climbed up into my small in-tank refugium:

http://www.inlandaquatics.com/images/borneman.jpg (this picture's not of mine, but they are very similar!)

...and proceeded to feast on all the copopods, small bristleworms, spaghettiworms, and other defenceless small fauna.

Next time someone utters the word "reef-safe", turn and run!