The pigbutt worm or flying buttocks (Chaetopterus pugaporcinus)

A Worm That Resembles a Disembodied Butt

This disembodied rump is a tiny worm known as Chaetopterus pugaporcinus. In 2006, researchers from the Monterey Bay Aquarium discovered this species bobbing along 3,000 feet deep under the Pacific Ocean. MBARI biologist Karen Osborn and her co-workers recently discovered a new species of deep-sea worm, but a worm like no other. The worm is round in shape, approximately the size of a hazelnut, and bears a strong resemblance to a disembodied pair of buttocks. Because of this, it was given a Latin species name Chaetopterus pugaporcinus that roughly translates to “resembling a pig’s rear.” Upon discovery, this worm earned some profoundly unfortunate monikers, such as “pigbutt worm” and “flying buttocks.”

Chaetopterus pugaporcinus flying buttocks

What appears to be the bull’s-eye at the center of the butthole is where the creature’s mouth is located. In order to feed, said mouth is surrounded by a “cloud of mucus” that catches organic detritus known as marine snow.
As far as their appearance goes, researchers at the aquarium offered up this explanation: “… researchers found that although the worms had segmented bodies, one of their middle segments was inflated like a balloon, giving the animals a distinctive gumball shape. All the other segments were compressed up against the front and back of the inflated segment, like a cartoon character whose nose and hind parts have been flattened in an unfortunate accident.”

Chaetopterus pugaporcinus flying buttocks
Image: Karen Osborn (c) 2006 MBARI

This photograph shows the back of the newly named worm. The concentric ovals are body segments that have been flattened against a single central segment that has ballooned out to form the bulk of the worm’s body.

Chaetopterus pugaporcinus flying buttocks


Image: Karen Osborn (c) 2006 MBARI

This photograph shows another view of Chaetopterus pugaporcinus, including its mouth parts.
Chaetopterus pugaporcinus flying buttocks
Image: Karen Osborn (c) 2006 MBARI

The researchers still aren’t sure if the worms they have been studying are larvae or adults. None of the individuals they collected had any identifiable sex organs, eggs, or sperm. Thus, they could be, as the authors put it, “wayward larvae, swept off the continental shelf and unable to settle [to the seafloor], thus growing to unusual size and developing adult features.”


Chaetopterid polychaetes, distinctive members of nearly all benthic marine communities, have larvae that may spend months in the plankton before settling to live their adult lives in parchment-like tubes attached to the sea floor. The cover image shows an extraordinary new species, Chaetopterus pugaporcinus, that may have relinquished the benthic portion of its life and made itself permanently at home in the pelagic realm. Chaetopterus pugaporcinus possesses the same combination of larval and adult features regardless of the size of the specimen (1 to 2 cm), and it has lost features associated with benthic life that were previously thought to be characteristic of the family. The species is reliably found off the coast of California at about 1000 m, regardless of the seafloor depth. One of its 15 segments is greatly expanded, while the others are compressed to the anterior and posterior poles of the decidedly non-vermiform body.
On pages 40-54 of this issue, Osborn et al. describe this new species and its ecology.

Chaetopterid polychaetes on journal cover

Credits: Photo, Karen J. Osborn (Monterey Bay Aquarium Research Institute); cover layout, Beth Liles, (Marine Biological Laboratory).

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