Whenever I work near the fish tank, I hear "Nemo" and " Dori" called out many times but this is my favorite fish- the pink spotted watchman goby. Hides a lot but does interesting things like grabbing rocks and shells for his( her?) home and sifting sand in his mouth for food.
I do not know why the photo adds upside down?! Also the squiggly things are the legs of a brittle star.