The phrase "sea squirts" refers to marine animals that resemble squishy, tubular sacks with small openings. They get their name because when squeezed, they squirt out water. Full definition
That marine biologist Ernst Haeckel's drawings of sea squirts resemble antique Christmas ornaments, or that his jellyfish look like the balusters of a Louis Sullivan staircase, is more than coincidental. (discovermagazine.com)
Most sea squirts are little more than rubbery blobs that stick to shells and rocks on the sea floor. (sciencemag.org)
If sea squirts, and not amphioxus, truly are the vertebrate's closest relative, then researchers studying vertebrate evolution may have to reinterpret morphological, developmental, and paleontological clues about how vertebrates got their start, concludes Philippe. (sciencemag.org)