Invertebrates
Ribbon Worm
Nemertea · also called ribbon worms, proboscis worms
A ribbon worm hunts with a weapon most animals do not have: a long, muscular tube normally kept turned inside out inside its own head, fired outward in an instant to wrap around, stab, or poison prey. One species, the bootlace worm, has been measured at over 55 metres — potentially making it the longest animal ever recorded, longer than a blue whale, despite being only millimetres wide.
Overview
Ribbon worms, phylum Nemertea, are marine predators found from shallow tide pools to the deep sea worldwide, with roughly 1,300 described species. They capture prey using an eversible proboscis, some armed with a sharp stylet and toxic secretions.
Stretching the definition of long
Highly elastic bodies mean length measurements depend heavily on how extended a worm is at the time — a key reason the bootlace worm’s record-breaking length claims carry some real uncertainty. Many species also show a striking capacity for regeneration, regrowing a complete new individual from a surviving fragment.
Status
Least Concern — abundant and diverse across marine habitats worldwide, with no evidence of broad population decline.
Ribbon Worm: common questions
How does a ribbon worm actually catch its prey?
A ribbon worm captures prey using its proboscis, a long, muscular tube normally held inside out within a fluid-filled internal cavity in the head, which the worm rapidly everts, essentially turning it inside out and shooting it outward toward a nearby prey item. Depending on the species, the proboscis may simply wrap tightly around the prey to restrain it, or in armed species it carries a sharp, dart-like stylet along with toxic secretions that help subdue the prey before the worm draws its proboscis, and the captured meal, back in to feed.
Is the bootlace worm really longer than a blue whale?
Historical measurements of the bootlace worm, a species of ribbon worm found in the North Sea, have reported lengths exceeding 55 metres in some specimens, which would indeed be considerably longer than even the largest blue whale, making it one of the strongest candidates for the longest animal ever recorded, though its body is only a few millimetres wide. Because ribbon worms are highly elastic and can stretch or contract their bodies substantially, exact length measurements can vary considerably depending on the state of the worm when measured, adding some uncertainty to the most extreme historical length claims.
Can a ribbon worm regrow its body if it is cut in half?
Many ribbon worm species have a notable capacity for regeneration, and some are capable of regrowing a complete, fully functional new individual from a surviving body fragment following injury or deliberate division, similar in principle to the regenerative abilities seen in some flatworms. This regenerative capacity likely provides a meaningful survival advantage in a marine environment where physical damage from predation attempts or environmental disturbance is a real and recurring risk.
Are ribbon worms dangerous to humans?
The great majority of ribbon worm species pose no meaningful danger to humans, being generally small, non-aggressive, and focused on hunting much smaller invertebrate prey using a proboscis designed for animals far smaller than a person. Some species do carry toxic secretions on their proboscis used to subdue prey, and handling certain ribbon worms carelessly could potentially cause mild skin irritation, but they are not considered a significant hazard to people under normal circumstances.