Any idea what this may be?

[LaneBrain]

Just noticed this growing on my hammer. At first I thought this may be some coral one but now I have other thoughts.
Any ideas?

 

[luu78]

Looks like sponge. You can scrape it off

 

[ChrisV]

Yes, a sponge

 

[BiGGiePauls33]

+3 on the sponge

 

[Zeefishies]

+4 sponge

 

[reefstarter]

Looks like sponge. You can scrape it off

Why would you scrape it off? Sponges are a good thing

 

[Chris A.]

Why would you scrape it off? Sponges are a good thing

Some sponges bore into lps skeletons

 

[dz6t]

Sponge can irritate coral even cover them and kill them.
Sponge on rock is good, not so good if it is on coral skeleton.