Biologist Jon Allen is the proud owner of the world's oldest ribbon worm on record.
The adopted invertebrate is fondly called Baseodiscus the Eldest, and he is at least 26 years old, probably around 30, according to a new analysis.
When fully stretched out, Baseodiscus, or 'B' for short, is roughly a meter (3 feet) long, but its age has been harder to pin down.
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Marine invertebrates are some of the longest-lived animals on the planet, and deep-sea tube worms can live for 300 years or possibly more.
Ribbon worms are particularly ubiquitous marine invertebrates, yet we know little of their lifespans.
B is the oldest recorded creature in the phylum Nemertea by a long shot. The only other contender Allen and his colleagues could find in the scientific literature was a ribbon worm just three years old.
"Ribbon worms are an incredibly diverse and widespread phylum, yet almost nothing is known about their natural longevity," says Allen.
"This finding fills a genuine knowledge gap, increasing their known lifespan by an order of magnitude. This shifts our understanding of an entire major group of marine predators."
Since 2005, Allen has kept B comfortable in a tank with lots of mud for meandering. The biologist first acquired the soft-bodied creature from the University of North Carolina's biology department after renovations disrupted its home.
While the marine invertebrate's exact birth date is unknown, Allen says that researchers collected B from the San Juan Islands as an adult sometime in the late 1990s.
In the past two decades alone, B has gone from living in Washington state to North Carolina to Maine to Virginia. He is a very well-travelled worm, indeed.
In 2024, a former student of Allen's convinced the biologist to get B genetically tested.
It turns out, the pet worm belongs to a species called Baseodiscus punnetti, only the second individual of its kind to be genetically barcoded.
Ribbon worms like B are not only long in the tooth, they are also surprisingly long in length.
A ribbon worm picked up on a Scottish beach in 1864 is thought to be the world's longest animal ever found alive. Some records suggest that when the washed-up worm was fully stretched out, it measured roughly twice the length of a blue whale.
Who knows how old that worm was?
"Marine worms may offer important insights into longevity research, and developing lifespan estimates for nemerteans will help researchers to better assess the ecological impact of these long‐lived benthic predators on marine ecosystems," Allen and colleagues conclude.
The study was published in the Journal of Experimental Zoology.