I have never seen these in my tank, but I found this (and what looks like some juvenile ones) in a container of sand I had scooped out to transfer to another tank (it was then sitting for a week so all those worms are now dead and probably crawled out of those shells. Any idea what kind these are? I haven't noticed any negative effects on my coral so I'm hoping these guys aren't fireworms because I bet there are more of them. It's hard for me to tell. That large one is half an inch long at most.


