What's on my live rock

So fairly new to this but got a biocube for my dad a few weeks ago for Father's day following that we got our live rock and on it I've found 3 urchins, a starfish, and a crab along with some shrimp that only come out at night but there is also what seems to be a red worm/tube that is in one of the holes and has a mouth like hole that opens and closes and we can't seem to figure out what it is. Then also with being fairly new to all of this is there any other advice you guys can give? We currently only have a clown fish and the tank is currently going through the brown algae phase

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