This milk-white colonial tunicate settled on an ideal spot for the holidays, with small specks of green algae poking through its tunic and bits of red and gold surrounding its body. Colonial tunicates are mat-like creatures made of dozens to hundreds of individuals called zooids. They live underwater, covering shellfish, barnacles or anything they can settle on. But this tunicate, Didemnum perlucidum, has another talent: It can make its own crystals. Invisible to the naked eye, its calcium carbonate “spicules” may help hold its outer tunic together—or help it defend itself from predators.
(Photo: Rosana M. Rocha, Universidade Federal do Paraná (UFPR), Brazil)