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Images: Big Trouble from Little Squirts

GROWING FROM THE BOTTOM UP—WHOI Scientist Mary Carman examines the invasive, filter-feeding sea squirt species of the genus Didemnum living in the tidepools at Sandwich Town Beach on Cape Cod. This species spreads up from the bottom of rocks as it grows, covering everything in its path, including vegetation and shellfish. "Anyone who likes to eat seafood should worry about this," Carman said. (Photo by Tom Kleindinst, WHOI Graphic Services)

MANY SQUIRTS, PACKED TOGETHER—Some species of sea squirts appear to be one large organism, but when viewed under a microscope, it is evident that they are actually a colony made of hundreds and thousands of tiny, linked "squirts," called zooids. Here, two species of sea squirts grow next to each other. The small, orange sea squirts are of the genus Botrylloides. The whitish, larger squirts are of the genus Didemnum. (Photo by Dann Blackwood, USGS)

LIVING WATER PISTOLS—As sea squirts feed on algae and bacteria, or when they are gently squeezed, they shoot water out of tiny pipes. These bursts of water give it the name "sea squirt." (Photo by Dann Blackwood, USGS)