Swollen zoanthid stem

[ReeferMaddness843]

So I've had this Zoa frag for a while now (4mos) and noticed this black tumor looking area on one polyp. This pic doesn't show it very well, so if better pic needed let me know and I'll try and get one first availability. The frag has steadily grown and have seen no ill effects. Just curious if anyone may know what would cause it. (It's the one on top right standing out) Thanks in advance for any help

 

[cloak]

It might be some sort of encrusting sponge. Generally these are harmless, but they have been known to smother corals before.

 

[ReeferMaddness843]

It looks like it's actually the neck of the Zoa expanded rather than something on it. Been there since received the frag. I'll try and get a better pic added tomorrow since tank just went blue. Thx