The main reason that the animal hadn't been spotted since 1873 is that it is very fragile, and tends to fall apart when dredged, said Karen Osborn, a study co-author and worm specialist at the Smithsonian's National Museum of Natural History. The dredging sled runs along the seafloor and knocks items into a net with a chain, which isn't exactly a gentle collecting technique, Osborn told LiveScience. Ideally, the animals are collected with submersibles, where they can be delicately plucked from the ocean bottom, she added.
The deep-sea acorn worms are quite different from their shallow-water relatives, which are more muscular, sturdier and easier to sample, Osborn said. The shallow-water variety also tend to dig burrows and siphon particles from the seafloor. This rediscovered species, however, crawls along the ocean bottom, eating particles of detritus.
"They are like little factories for digesting organic matter," Osborn said.
Acorn worms get their name from their proboscis, which resembles the cap of an acorn, Osborn said. Recent studies of which Osborn has been a part have identified more than a dozen new species of acorn worms. The present study was led by Nicholas Holland, a researcher at the Scripps Institution of Oceanography.