Invertebrates
Peanut Worm
Sipuncula · also called sipunculids
Disturb a peanut worm mid-feed and it pulls its entire extended feeding structure back inside its own body in an instant, contracting into a plump, wrinkled shape that looks remarkably like an unshelled peanut left lying on the seafloor.
Overview
The peanut worm, phylum Sipuncula, is a burrowing marine worm found across coastal and ocean habitat worldwide. Its distinctive retractable feeding structure and lack of close relation to true segmented worms make it a genuinely separate branch on the invertebrate family tree.
A body built to disappear
Rather than fleeing or fighting when disturbed, the peanut worm simply withdraws, pulling its vulnerable feeding structure entirely inside its own body until the threat passes, a defense as simple as it is effective.
Status
Not Evaluated — no formal conservation assessment completed, with the group remaining generally common across its extensive marine range.
Peanut Worm: common questions
Why is it called a peanut worm?
A peanut worm can fully retract its extendable feeding structure, called an introvert, back into its main body, causing the whole animal to contract into a plump, wrinkled shape that resembles an unshelled peanut, a transformation directly responsible for the common name given to this group of marine worms.
Is the peanut worm related to earthworms or other segmented worms?
No, despite superficially resembling other marine worms, a peanut worm belongs to its own distinct group, Sipuncula, and is not closely related to true segmented worms, or annelids, such as earthworms, despite sharing a generally similar soft, elongated body shape.
How does a peanut worm feed?
A peanut worm feeds using an extendable structure called an introvert, tipped with tentacles or a specialised mouth region, which it extends outward from its burrow to gather organic particles and sediment before retracting the whole structure back into the body for protection.
Where do peanut worms live?
Peanut worm species are found across coastal and marine habitat in oceans worldwide, generally living burrowed within sand, mud, or narrow rock crevices along the seafloor, from shallow coastal water to considerable ocean depth.