Watery Whoopee Cushion?
Or is it a hot water bottle? This little orange bag is no container, it’s the "tunic" or leathery, bag-like outer covering of our chordate cousin, the sea squirt. This ocean-dweller has a peculiar life cycle. In its larval stage the sea squirt has a notochord (elastic rod) - much like a true backbone - that extends the length of its tadpole-shaped body. Once the larva chooses a stable object as a home, it attaches itself and proceeds to digest its notochord and other organs. The sea squirt then grows its tunic that protects the inner animal. The two siphons (spout-like openings) control the flow of water into and out of the tunic. As water flows into the tunic through the incurrent siphon, the sea squirt’s digestive organs filter out the plankton; the remaining water is expelled through the excurrent siphon.

Since the squirt remains attached to the same object throughout its life, its choice of location is crucial. Because sea squirts are stationary, they are easy prey. To deter predators some sea squirts secret sulfuric acid while others emit toxic metals such as vanadium. These defenses don’t deter the squirt-loving Koreans, who consider sea squirt a delicacy. Sea squirts have also been used to develop an anti-tumor drug called ecteinascidin that is being tested on terminally ill patients suffering from soft-tissue cancers. If that weren’t enough, the sea squirt has even been the muse of Hanna-Barbera cartoonists.