We've noticed a few hitchhikers in our tank, I'm sure there's more to come.
So far we've observed a featherduster worm, and a few snails.
While I was doing the rockwork I noticed a large crab (about the size of a toonie) way up in a deep crevice of one of my rocks. He was brown with red eyes, didn't look hairy at all. He was to deep in the rock to get out, so I let him be, I hope this doesn't turn out to be a mistake. I seem to recall reading on the forums somewhere that hairy crab=bad crab, and non-hairy crab=good crab. I'm hoping this is the case with this guy, who knows if he'll survive the cycle though.
We also found this guy:
MANTIS!!! My wife thought it was cool that she could see "yellow eyes" watching her from inside a rock, I didn't think it was so cool. The rock was at the bottom of the rockwork, but luckily was not load bearing and easily removed.
I wish I had a place to put him, or some fish to feed him to, but alas his fate was simply to end up in the garbage
Couldn't have him in my tank though. I hope there aren't any more in there.
I also found a small crab (about the size of a dime) climbing around on the rock that the mantis came out of. I decided to be safe and threw him in the refugium.