Sponge question

[jmorgret]

I have a piece of rock, about the size of a baseball. There was what appeared to be a white sponge growing on the bottom. Over the last 6 months, the has spread to cover almost the entire underneath of the rock. It almost looks like a dense spider web. Was just wondering if this is normal or not. It doesn't appear to like to top part of the rock facing the light.

[Reefkeepjeweler]

Sounds like a sponge to me. They are harmless hitchhikers on live rock sometimes. They don't like bright light and tend to grow in areas where light is not as prevalent.