Whats growing on my Hammer

[flipboard7431]

I noticed this white stuff around the flesh band of the hammer, any advice is appreciated!

 

[Tahoe61]

Based on the location I would say mesenterial filaments, the internal structures of corals and some inverts.
Sponge would be my second guess.

 

[YSreef]

Could be its fleshband is growing as well