tubes

Hi all, A short intro: I'm new here, but have had a salt water tank for approximately 2 years. I've only ever had corals, clowns, emerald crabs, coral-banded shrimp, gobys & snails. That being said, my current tank consists of a clown, an emerald crab, 4 turbo snails & a conch snail, along...

Not sure what these are, I just spotted them today on my dry rock that has been in the tank for about 3 months. Only other things in the tank are 2 clowns, urchine, zoa, mix of snails and a xenia coral which btw happens to be right next to the rock that has these things on them. Thanks!