possible pest?

This thing is tube shaped and I just noticed it today. I regularly look at this part of the tank as it is where my pistol shrimp and goby routinely have their cave entrance. I have sand and rubble harvested direct from the ocean in this tank. Tank is mature and well established.

I've had this chalice for a few years now and I'm pretty sure that I've never seen this before. Are these some sort of worms? Is it an issue that I need to worry about?

Hey guys, I recently moved some rocks from another tank into this system and found this little guy in the sand bed moving about. any possible ideas and should it be pulled? (Asking since I don’t think I would have the space to add a fish that would be a predator to the starfish incase I become...

Hey so I moved my snail (I think it’s a turbo) and hermit crab from my other tank into this one. I didn’t do an official QT, I just scrubbed the shells really well in a bowl of new + old tank water and then once really clean I dunked them separately in a new dish of RODI. I thought that would be...

I just added 2 banggai cardinal, a YWG, a green mandarin goby, a blue hippo tang, and a flame angelfish from DR Reef's quarantine fish to my 200 gallon reefer xl Unfortunately the flame angel, one cardinal, and the YWG all died within 3 days. Water parameters are normal and the other fish are...

I have a swarm of free swimming little white bugs in my tank and it’s tripping me out. They look like little white shrimp but hang upside down like mosquito larvae. Are they some type of pod? Or do I have a problem?