Photo ID: Bubble Algae? Egg Sac?

[ariellemermaid]

Looking for help identifying this spot at the base of a coral frag. A couple of weeks ago we identified two spheres on this plug: one was tan and the pictured one is more black.

Background: invertebrate only QT tank, never seen a fish. Current stocking is hermits, snails, emerald crab, Pom Pom crab, conch, starfish, cleaner clam, corals, and a pistol shrimp.

This doesn’t seem to fit the idea of bubble algae. In weeks we’ve gone from two spots to one. It’s fairly large and looks more...intentional than bubble algae (although we’ve never dealt with bubble algae).

Bonus: it looks like we have a feather duster worm hitchhiker growing at the base of this acro we killed. Confirm?

 

[Saltyreef]

Yes harmless feather duster. And i believe the other a piece of bubble algae.
Pull it off with some foreceps if you dont like it.