What is growing in my overflow?

[craiginphoenix]

Anyone know that this white stringy stuff is growing in my overflow? I don't see it anywhere else in the tank. Is it aptasia?

 

[ISpeakForTheSeas]

Sponges - harmless filter-feeders.

 

[craiginphoenix]

Sponges - harmless filter-feeders.

Thanks! Was a little nervous but assumed since it wasn't anywhere else in the tank it was fine.