What could this be?

[Ghost noogies]

Was dipping my green Monti and noticed this hole, then something popped out.

[Reefpuck]

Could be a number of things...hard to tell from photo. Definitely wouldn't put it in your tank until you find out.

[Sugar Magnolia]

Could be a gall crab.

[mcgyvr]

No description?..
Barnacle?

[Ghost noogies]

Damn.... It is a gall crab.�� Good call Sugar Magnolia. Now to extract