Wow, nice live rock which such interesting hitchhikers.
Allow me to recommend my favoriate reef aquaria forum, Reef Central.
There you will find the Ask Dr. Ron forum where he can identify just about anything that can be identified without dissection.
FWIW, I’d hazard a guess that it’s probably carnivorous and unwelcome in your tank.
in a tube about 1/2" across and 3/4" deep a little dude w/ what looks like an orange hardhat w/ two eye stalks pops out, he puts out these two little arms that look like they have brown SPIRALED featherdusters on them… what is THAT about?!