6 September 2012

Pigbutt worm

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In the depths of the oceans, kilometres below the surface, you’d expect to find peculiar things. No one, however, expected to discover a floating pair of buttocks.
PIgbutt worm

The cheeky pigbutt worm, a very strange shape indeed. Credit: Casey Dunn

In the depths of the oceans, kilometres below the surface, you’d expect to find peculiar things. In fact, researchers routinely send remotely operated vehicles (ROVs) down in the hope of glimpsing never-before-seen species. No one, however, expected to discover a floating pair of buttocks.

Venturing into the deep sea now requires an additional warning: ladies and gentlemen, expect to be mooned by the pigbutt worm (Chaetopterus pugaporcinus). Discovered in 2007 by Karen Osborn and colleagues from the Monterey Bay Aquarium Research Institute in the U.S., the California Institute of Technology and the South Australian Museum, this worm’s odd shape appears to have been influenced by its free-floating lifestyle.

“Organisms in the midwater [everything below the ocean surface and above the deep sea floor] experience such different conditions that they often have to change their morphology and behaviour dramatically to survive,” explained Osborn, a marine biologist from the Smithsonian National Museum of Natural History, in the U.S.

The pigbutt worm lives off the Californian coast, at depths between 900 and 1,200m, just below the Oxygen Minimum Zone (OMZ). They are technically a member of the Chaetopterid family of segmented worms that usually live in parchment-like tubes attached to rocks or in sea-floor mud. But the rotund pigbutt worm bucks the trend, floating around in the water column far above the sea floor. Researchers think they could be larval worms but they aren’t so sure. The size of hazelnuts, pigbutt worms are 10 times the size of most Chaetopterid larvae and have lost several key larval features, said Osborn. Just why they ended up looking and behaving so differently from the other members of their family remains a mystery.

“It may be that the larvae missed their cue to settle out to the sea floor or never found suitable habitat, but that seems unlikely, considering the consistency with which we find them in a specific midwater habitat and the consistency of their morphology, no matter what size they are.” They range from 12 to 23mm long.

Osborn’s team is responsible for the discovery of other strange sea creatures, including drifting acorn worms, green bomber worms, squidworms and feather-foot ‘spider’ isopods.

“The deep water column is full of delicate, beautifully bizarre animals no one has ever seen before,” she said. “Exploration with ROVs or other submersibles allows us to observe and collect specimens that we can study. This in turn allows us to better understand how the oceans function and the true impact [humans] have on them.”

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