small white balls of 'fuzz' on my macro

[KurtS]

Does anyone know what this might be?

I have noticed several growing on my macro lately, I would estimate they are about 3 to 4mm in diameter now and they only grow on the macro.

 

First I thought it might be some kind of sponge but now that they are larger I can distinguish what appears to a 'mouth' of some kind and there seem to be growing hairs on the sides.

 

(click photo for full res image and more detail, fair warning: it is an 18mp image)

[GHill762]

pineapple sponge.. harmless filter feeders.

[KurtS]

Thanks for the quick reply, they'll be staying then