What is this?

[cbrine]

Originally Posted by Lindsey

How would you recommend I kill them? My lfs told me they were nothing to be concerned about so we left them and now they have multiplied real quick.

If its on a easy to remove piece of LR, take it out and using a small needle/syrine inject the base with lemon juice. As they are tricky little boogers and will retract if it does this, just fill a small bucket of tank water and then submerge the rock until it comes back out, then stab it at the base.
~just be careful that you watch your water params as the lemon juice can dip some of your values. Then just do a small water change - no harm will come to your tank/livestock.

I found this to be the cheapest and easiest way to rid of the pests, can also try getting a peppermint shrimp to eat it (which may or may not work). I would lend you mine, but the last person to "borrow" it, has not returned him.