Thousands of different species of organisms live in the water we row in and on the docks and shores we row past. The size of these species range from whales 10 meters long to bacteria and viruses about a micro-meter in diameter. To the unaided eye the whale is most spectacular, but a microscope reveals another world, perhaps even more fantastic. Smaller organisms represent a greater number of species and constitute a larger total mass. Each organism is small, but there are so many of them. In this exhibit I focus on one animal, Botryllus violaceus, in the middle of this size range.
B. violaceus is a member of the tunicate phylum, named for its protective gel coat (the tunic). They are known commonly as a sea squirts, because if you squeeze them they squirt water. More specifically, B. violaceus is a member of class ascidiacea because the adult is fixed to a solid surface; members of other classes float freely in the ocean. Individual adults, called zooids, form large colonies, while other species of ascidians remain solitary.