Help Growing on rock

[mrred]

Can anyone identify this? Slick matted and long string like areas. Its growing in a low light condition.

 

[evolved]

Harmless sponges

 

[ReeferBean]

If it bothers you just pull a little off. That type seems to grow pretty fast but like you said in low light areas for the most part.

 

[mrred]

Thanks for the info. It just looked nasty, I cleaned it off and move the rock.