This Worm Has No Ifs And Many Butts

In the 1870s, as the research ship HMS Challenger passed through the Philippines during its circumnavigation of the Earth, it dredged up a sponge from the gray sludge 95 fathoms (nearly 600 feet) below the surface. The scientists knew that glass sponges abounded in these waters, their bodies fragile, translucent, and curiously geometric. Sponges of this sort often house other animals, such as monogamous shrimp and various worms. So it was not exactly revelatory that the dredged-up sponge contained a worm, but the worm itself was a revelation. It had laced its body through the sponge's many passages, so much so that it might have resembled many worms. But it was just one worm whose body appeared able to branch like a tree. "The body of the annelid appears to have a furor for budding," the zoologist W. C. M'Intosh wrote in an 1879 paper describing the preserved specimen of the worm. Although M'Intosh did not comprehend this at the time, the worm had a furor for budding multiple anuses. Maria Teresa Aguado, an evolutionary biologist at the University of Göttingen in Germany, learned about branching worms as a PhD student. She had always romanticized the Challenger expedition and imagined what it was like to explore distant oceans and glimpse the life lurking at great depths. When she came across an illustration of the branching worm found off the Philippines, now called Syllis ramosa, the worm sparked a lifelong fascination. "I remember staring at it, wondering if such a creature could really exist," she wrote in an email. "How could an animal evolve such a bizarre body plan?" For more than a century, branching worms seemed extraordinarily rare, with only a single species described by science. There were some reports of branching worms found elsewhere around the world, in the Red, Tasman, and Arafuro Seas, all identified as S. ramosa. But in 2012, Aguado and colleagues found a second species of branching worm off of northern Australia, and then a third species off an island in Japan. Aguado began to suspect that branching worms were not so rare after all. "Perhaps there were many more species, and the old records weren’t just about one or two isolated cases, but about a widespread and diverse group," she said. She was right; in September, Aguado and colleagues published a paper in the Zoological Journal of the Linnean Society that describes 10 probable new species of branching worms and reconstructs the evolutionary history of the strange group.

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