Weird stringy mass on rock

[silly_blenny]

I was doing some maintenance when I noticed this weird stringy mass for the first time on my rock work. It had been hidden by a large discosoma, and I noticed this when I removed the coral (didn’t like where it ended up). Any idea what it could be? The tank has been eatablished for over 2.5 years, and the only recent addition were a couple of pitho crabs.

 

[Dan_P]

I was doing some maintenance when I noticed this weird stringy mass for the first time on my rock work. It had been hidden by a large discosoma, and I noticed this when I removed the coral (didn’t like where it ended up). Any idea what it could be? The tank has been eatablished for over 2.5 years, and the only recent addition were a couple of pitho crabs.

Looks like a sponge

 

[EnterName]

Jepp, sponge. Most likely harmless filter feeder.

There are a few sponges that grow aggressively and can even grow over corals but if that one was below a coral it might prefer cryptic areas without much light and won't cause issues. I would just leave it

Scraping it off would potentially cause it to spread and regrow. See page 5, post #82 for more details on sponges' regenerative abilities: https://www.reef2reef.com/threads/microscopy-thread.1138845/post-14426492