These are at the base of a coral I dipped last week due to spionid worms. These look different but could the be spionid? The have some sort of tube structure, then a bunch of white flowing tentacles. The spionid worms just had two antennas which is why I think this is different. What should I do about them?
I dont know what they are, but i have them too. The reason I have them is my tank died last year and instead of quitting I decided to let it run and mature. Now I have a lot of them. My Diamond goby picks them up and stacks them into a pile and I scoop them up and throw them out.
I do not think they're harmful, but they can be annoying. I have not had any problems with them. They like to take shelter under frag plugs and rocks, but sometimes they will poke up right out of open sand.