live rock and live sand

[lightfoot]

I bought live fiji rock and in several places on the rock are these yellow masses that look like spider egg sacks, there is one big one that opens and closes what are these.
also I have about an inch of live sand what is a good level and should I add any sand sifting star fish or something like this to turn the sand.

 

[mr . salty]

Not sure what those things on the rock could be...For a sand bed to be functionable,it should be at least three inches deep.

 

[billyv]

It could be a sponge. I have a bright yellow sponge that popped up on my live rock.