I've spotted this weird little tunicate growing. I thought it was odd that it was right out in the open in high flow under bright lights. Sponges usually like to hide.

The little spicule poking out is what has me confused, though. I've never seen a tunicate have an appendage. Sometimes it's visible, sometimes it's not. I haven't noticed a pattern to its visibility.

This shot was taken yesterday around this time when it was sticking out further than usual. Now today it's just the tunicate with no spike. What's going on?