Rippling among blades of kelp or striking suddenly from sandy burrows, ribbon worms lurk through intertidal waters in search of their next target. These very thin, stretchy, and sometimes flamboyantly colorful worms are adept predators. To hunt their prey—including crustaceans, barnacles, clams, snails and annelid worms—ribbon worms shoot a mucus-slathered proboscis from their nose cavity, like a toxic lasso. They then inject their prey with a venomous cocktail, paralyzing and liquefying it so that they can slurp out its tissues.
Scientifically known as nemerteans, ribbon worms are unique enough to belong in their very own phylum, Nemertea. Worldwide, about 1,300 species of ribbon worms have been described, though researchers speculate that a majority of them remain undiscovered. Last summer, a University of California, Davis undergraduate researcher, Maddy Frey, set out to survey Bodega Bay’s ribbon worm diversity—and found 34 species, one-third of which are completely new to science.
“I never would have guessed that we’d find 11 new species, right here in our backyard, in such a short amount of time,” says Eric Sanford, a UC Davis marine invertebrate ecologist who supervised Frey’s work.
“We still need this very basic science; we don’t have good records of biodiversity,” says Peter Roopnarine, a marine invertebrate ecologist at the California Academy of Sciences. Roopnarine, who was not involved in the Bodega Bay study, was pleased to see a baseline biodiversity survey of these often-overlooked marine invertebrates. “In terms of sheer biomass, invertebrates dominate the ocean ecosystem, and yet we know a lot about some groups and very little about most groups.”
How a worm hunt happened
Ribbon worms range from translucent strands less than a millimeter long to the longest animal documented on Earth. The European bootlace worm (Lineus longissimus) has been estimated to reach 180 feet when stretched out, longer than a blue whale. Ribbon worms are common throughout the California coast, living among kelp holdfasts and eelgrass roots, or burrowing in sediment and under rocks.
Frey took a liking to ribbon worms in Sanford’s marine invertebrate ecology class, and pursued a UC Natural Reserve System grant to spend a summer surveying them. She set out with a trowel and bucket to collect as many ribbon worms as she could throughout the nooks and crannies of Bodega Bay. On a sandy beach just outside the marine lab, Frey scooped up a 10-centimeter-long, creamy white worm with swirls of pink cerebral ganglia—worm brains—showing through its skin. It turned out to be a previously unidentified species.
Identifying ribbon worms by looks alone is tricky, and taxonomy guides are incomplete at best. Frey and Sanford sent their samples to Svetlana Maslakova, a world expert on ribbon worms at the University of Oregon who has compiled a database of their genetic diversity.
“So many species are undescribed that we can’t make head or tail of it until we get them DNA barcoded,” says Maslakova, who became fascinated by nemerteans as a graduate student. When she learned that almost nobody studied them, Maslakova took on the mission of discovering and documenting them.
At Maslakova’s lab, Christina Ellison, a graduate student, extracted the Bodega Bay ribbon worms’ DNA, sequenced it, and matched the sequences to the database. Some ribbon worms have only been identified using genetic sequencing from larvae, without scientists knowing what their adult forms look like or where they live.
As larvae, ribbon worms drift in the open ocean as plankton. Many look like miniature wormy adults. Those in the class Pilidiophora look like little hats, and grow their juvenile worm forms inside their larval bodies, curled around their guts. Once the juvenile is ready, the worm punctures a hole through its own larval skin and turns inside out while swallowing itself.
This process, known as catastrophic metamorphosis, is “kind of like pulling a sweater over your head, but eating your body while you’re backing out,” says Ellison.
‘How little we know’
Of the 34 ribbon worms sampled and sequenced from Bodega Bay, 13 could be assigned to described species, 10 matched species in the database that have yet to be named (official naming takes time), and 11 were completely new to science.
“It illustrates just how little we know,” says Maslakova. “If we don’t know what’s there, we can’t monitor it and see what changes with climate change and habitat degradation.”
Roopnarine was surprised not to see certain ribbon worm species common to the northern California coast in the Bodega Bay study. He wonders if some worms may undergo boom-and-bust cycles over the years—or if species ranges may be shifting because of climate change. Though Frey’s summer project was a one-off, Sanford hopes to do similar surveys of other overlooked groups, such as sea spiders or bryozoans, in the future.
“Even in well-studied coastal California, there’s a lot of biodiversity left to be discovered and described,” says Sanford. “If we want to understand how our coastal ecosystems are changing due to climate change or other human impacts, we really need a good understanding of what biodiversity is present out there.”
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