Meet “Baseodiscus the Elderest”, a record worm over 27 years old

Ribbon worms can reach enormous lengths, and one of them named Baseodiscus the eldest shows how little we know about them, including how long they live

By Marina Wang edited by Andrea Thompson

Each year, Jon Allen, associate professor of marine biology at William & Mary, gently removes anemones and brittle stars from a saltwater tank. He then searches the mud for his nearly meter-long ribbon worm, named Baseodiscus the eldest according to his gender, to show his invertebrate zoology class.

When people imagine worms, they often imagine ordinary earthworms, but ribbon worms wiggle on a distant evolutionary branch and burrow primarily in seabeds or rocky shores. Most of the approximately 1,300 species of ribbon worms are only a few millimeters wide and can be quite long: one species, A very long queuecan measure up to 55 meters, twice the average length of a blue whale. “They’re basically long, fairly flat, ribbon-like worms,” Allen says. “They are really voracious predators in the marine system.”

Baseodiscus the eldest, or B, as it is called for short, was caught in the wild between 1996 and 1998 and kept in a tank at the University of North Carolina at Chapel Hill. It came into Allen’s possession when the building in which it was kept was renovated.

On supporting science journalism

If you enjoy this article, please consider supporting our award-winning journalism by subscribe. By purchasing a subscription, you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

When Allen showed B to his class in 2023, Chloe Goodsell, then an undergraduate, was surprised. She took care of the anemones and sea urchins sharing B’s tank and didn’t even know the worm lived there. She began asking Allen questions such as how old the worm was. It turned out that neither Allen nor any other scientist knew the answer.

The investigation prompted Allen and Goodsell to publish an article in the Journal of Experimental Zoology estimate of B’s ​​age: at least, the worm is 27 years old. It’s a new record for ribbon worms; the previous record holder was three years old. “B is older than my co-author,” Allen says with a laugh. The worm’s longevity sheds new light on the lifespan of ribbon worms and how little we know about them.

The upper age limit for these worms is not yet known, and B’s age could be decades older than the current estimate of their maximum lifespan, Allen says. He thinks B is probably average for his species because he doesn’t give the worm any special care or feeding from Allen (B probably survived on a population of peanut worms coexisting in the aquarium). Many marine invertebrates can live incredible lifespans, with some deep-sea tube worms reaching 300 years and a clam off the coast of Iceland being over 500 years old. Ribbon worms are also relatively large and top predators, as are many longer-lived species. “Who’s to say that a tapeworm can’t live to be 100, 200 or 300 years old?” Allen asks.

“It’s quite interesting to think about why different organisms evolve long lifespans and how they can live so long,” says Goodsell, now a Ph.D. student at the University of California, Irvine. “There is much to learn from the worms of the world.”

Eric Sanford, a marine ecologist at the University of California, Davis, who was not involved in the study, says age is crucial background information for scientists who might be interested in studying how many offspring worms can have over their lifetime and how worm populations might affect other animals they prey on.

Meanwhile, B is constantly extending the known lifespan of his species, but no one knows for how much longer. “Every year it’s a bit of a mystery: will it still be there? Allen said.