ID Please

[Mish1]

I have noticed this bulge growing on the frag plug at the base of a Green Humilis Acropora. It almost appears shell like and I see two black what appear to be antenna or something coming out. Definitely some type of invertebrate but I don't know if it is good or bad. Sorry for the terrible photo quality. It is tiny so it is tough to get a good picture of it.

 

[Michael Hoaster]

We need a better pic. Does it move? Is it encrusted on the rock? Do the antenna thingies retract? At this point I'd guess sponge or sea squirt.

 

[Mish1]

It does not move and seems to be attached to the rock. It has doubled in size in about 2 months. The two antenna do retract and when they come out they come out about an inch. Here is a different angle.

 

[Sugar Magnolia]

I'll second a sea squirt but your pictures aren't clear enough for a positive ID.