ID please - new guest in my tank

[reefm]

I just noticed these soft white vain-type lines under one of my rock structures, any idea what they are? So far, they haven't spread anywhere else.

thanks!

 

[shoelaceike]

Sponge

 

[Psiber_Syn]

+1

 

[reefm]

Instant answers, only in reef2reef! Thank you, greatly appreciated

 

[MURedhawk]

Possibly sponge or tunicates. Tough to tell even zooming in on picture.