Yellow Tube/Sac Under My Acan?

I apologize for the low light, but I can only see it when the acans shrink at night. It almost looks like a little sponge, but it almost has the appearance of being full of eggs. That could just be the texture of the sponge, I suppose. Kind of a translucent appearance with a little tube at the end.

 

It's indeed a sponge, you need to trust your instincts. The spout you're seeing is called an Osculum.

The variety in the image is harmless, sponges need silicates to really take off. In newer tanks there tends to be more silicates, even moved tanks. Personally I am big fan of sponges, most are non-photosynthetic and simple filter feeders.

 

I spy with my little eye, pineapple sponges.

 

pineapple sponges come in yellow?

 

My instinct is that my corals are surrounded by deadly, mysterious growths that are trying to kill them! Ha ha ha. I need to develop the right instincts. Thanks for all your help, guys. I can't tell you how much it's appreciated.