Shell?

This is a picture of, what I think, is some kind of shell on a brain coral. This is in Grand Cayman. Am I correct? Thanks

Im not sure it is a shell. Its more likely something that is burrowing into the coral like a christmas tree worm

Agreed. Looks like a retracted worm, although not a Christmas tree worm since their base looks different.

It may be hard to identify which worm since most worm pics online only show the extended creature.

Search for feather and fan worms to see some images of the full creature.

23 minutes ago, giffenk said:

Search for feather and fan worms to see some images of the full creature

Thanks for the suggestion. As you can expect, lot's of pictures of worms that are open. Haven't found any pictures of those retracted/closed. Fortunately, I found some YouTubes. Here's one that shows what Giggenk and Kdgonzalez suggested. Looks like a retracted worm https://www.shutterstock.com/video/clip-6007769-feather-duster-fan-worm-retracting-back-into

yes, its the soft tube of a sabellid polychaete