what is this large red thing

I bought a some live rock from the LFS yesterday and It had a large red protuberance about 3 1/2 inches long. I just thought it was a coralline algae covered piece of rock until......I put it in the tank and I noticed an opening in the end. I put a net near it, didn't even touch it and it closed. So all I know is it IS alive, doesn't like nets, and thats about it. I rather new to this and I was hoping someone could tell what this is, is it good or bad, and what do I need to feed it. Thanks in advance.

 

Some type of sea squirt.

 

would that be good, bad or neither? what do I feed the thing? thanks

 

It's a good freebie. If I'm not mistaken, they do require regular feedings of phytoplankton. Not sure how much you'd need to keep that particular species alive so hopefully somebody with more experience will chime in.

 

I have about a dozen translucent blue tube sea squirts in my tank. I haven't fed them ever. They should be self sufficient on particles in the water (fish and food wastes, cleaning algae off of glass, etc). Mine are not only alive but thriving and growing.

The thing in your picture doesn't look anything like mine, but it's definitely some sort of filter feeder.

 

It's definitely a sea squirt/tunicate/ascidian

Whether or not they need to be fed is going to vary depending on everyones tank. Some people specialize in corals that require nutrient poor water. If that's what your tank is like, you'll likely need to target feed it.