Pigbutt worm
Encyclopedia
The pigbutt worm or flying buttocks (Chaetopterus pugaporcinus) is a newly discovered species of worm found by scientists at the Monterey Bay Aquarium Research Institute
Monterey Bay Aquarium Research Institute
The Monterey Bay Aquarium Research Institute is a not-for-profit oceanographic research center in Moss Landing, California affiliated with the Monterey Bay Aquarium. It was founded in 1987 by David Packard of Hewlett-Packard fame...

. The worm is round in shape, approximately the size of a hazelnut
Hazelnut
A hazelnut is the nut of the hazel and is also known as a cob nut or filbert nut according to species. A cob is roughly spherical to oval, about 15–25 mm long and 10–15 mm in diameter, with an outer fibrous husk surrounding a smooth shell. A filbert is more elongated, being about twice...

, and bears a strong resemblance to a disembodied pair of buttocks. Because of this, it was given a Latin species name that roughly translates to "resembling a pig's rear."

The worm has been recently observed residing just below the oxygen minimum zone
Oxygen minimum zone
The Oxygen minimum zone , sometimes referred to as the shadow zone, is the zone in which oxygen saturation in seawater in the ocean is at its lowest. This zone occurs at depths of about 200 to 1,000 metres, depending on local circumstances....

 between 900 and 1,200 metres (3,000 to 4,000 feet) deep — even when the sea floor is significantly deeper. The worms have also been observed floating with their mouths surrounded by a cloud of mucus. Current theories suggest that they reside in this area of the ocean because of its cornucopia of detritus and marine snow
Marine snow
In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below. The term was first coined by the explorer William Beebe as he...

, and that the worms use these mucus clouds to capture particles of food and "snow."

The worm has a segmented body, but the middle segments are highly inflated, giving the animal a round shape. These morphological characteristics
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 are unique among chaetopterids. It is unknown whether the specimens found to date were adult or larval forms. Their unusual size (five to ten times larger than any known chaetopterid larvae) might indicate they were adults, but all known species of chaetopterid adults live in parchment-like tubes on the sea floor. Comparison to larval morphology has indicated that the specimens have a close relationship to either genus Chaetopterus or genus Mesochaetopterus, and a phylogenetic tree
Phylogenetic tree
A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...

 constructed from mitochondrial and ribosomal DNA sequences from twelve different Chaetopteridae worms found them to be most closely related to other worms of the Chaetopterus genus.

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