What IS That Thang?

[octopuppy]

Daytime shore dive off of Scuba Club Cozumel. In ~16' of water between blocks of concrete rubble just off Scuba Club dock. About 1.5" across and 2" high.

Barnacle? Appreciate your help.

 

[under water]

This is a worm, a sabellariid, tube-dwelling polychaete worm.
I saw one right there as well.. see near bottom of this page.

Cozumel Shore Diving

 

[octopuppy]

Thanks, I believe that's it. Nice photos!