I was diving Ligpo...I was diving Eagle Point...I was diving Twin Rocks. Actually, it does not matter where I was diving. Every reasonably healthy tropical reef I've visited is literally covered in them. Whether white-bodied with dramatically purple veins; or a collection of royal blue tubes; or yellowish-green organ pipes; or a colony of brownish perforated mats; the variety of colors, shapes, and sizes of this class of organism is only matched by its ubiquity. Today, I am pleased to introduce the tunicate - also known as the sea squirt - one of the most widespread and successful animals on the reef.