Need advice on nasty hitchhikers

[Shawner9ster]

I have many problematic inverts in my tank that came free of charge on/in liverock whan i started my 75g over a year ago. They are now of a size that they now prey on hermitcrabs, snails, and now starting on mushrooms and polyps. I know the culprits for the snails and hermits are a couple of mantis shrimp as i have seen them. I also know I have three unidentified crabs wandering around my tank. One is a larger purple crab that seems content to graze on asorted algea. One is a hairy tan coloured fellow that is in hiding most of the time. And the last is one I found the other day that seems to be hiding out in the sand, he is also tan in colour. All are around 3-4cm wide plus legs! Finally today, I found what seems like a tube-trail with little pieces of rock on the outside. It looks like some kinda worm is boaring through liverock and chowin down on corals. I could use some help on ideas on how to remove the "undesireables" from my tank and if possible some IDs. Should I be concerned of the crabs?
Thanks for any and all help in advance.
Shawn