What is growing on my frogspawn?

From this shot you can see the growth, the whitish spherical bit that starts right where the flesh of the frogspawn ends. It can change in size, growing and shrinking like a LPS coral would, and seems to have a mouth (can be seen in the second picture, below). The mouth is often open, but sometimes totally disappears. It's usually the size it is in the picture, but sometimes can shrink down to half the size; sometimes it is darker and sometimes it is lighter...just the mouth, the actual sphere always stays that whitish color.