What is this? I'm a bit nervous

I have this growth on one of my live rocks. It looks like a caterpillar cocoon. Has anyone seen something like this before? Should I be concerned?

looks like a sponge, nothing to worry about

Hrmm, I did some further investigation and it seems to be a fungus caused from excess foods.
Link to a similar post: http://www.myaquariumclub.com/i-not...tton/cocoon-like-on-one-of-my...-7663217.html

Most likely caused by over feeding. I'm assuming it's because I was attempting to get my new firefish to eat. Nothing a few water changes and manual removal can't fix.