Pigbutt worm

The pigbutt worm or flying buttocks (Chaetopterus pugaporcinus) is a species of worm found by scientists at the Monterey Bay Aquarium Research Institute.^[1] 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 that roughly translates to "resembling a pig's rear.

The worm has been observed residing just below the oxygen minimum zone 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, 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 are unique amongchaetopterids. 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 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.