Study: Sea spiders use guts to pump oxygen

WASHINGTON — Most animals depend on a beating heart to pump blood and oxygen, but sea spiders do this mostly with their unusual guts, according to a new study published on Monday.

“Unlike us, with our centrally located guts that are all confined to a single body cavity, the guts of sea spiders branch multiple times and sections of gut tube go down to the end of every leg,” lead author H. Arthur Woods of the University of Montana, Missoula, said in a statement.

“In effect, sea spiders guts are ‘space-filling’ and ubiquitous in their bodies in the same way that our circulatory systems are space-filling and ubiquitous.”

The study, published in the journal Current Biology, found that sea spiders, which take in oxygen directly through their cuticles, use peristalsis to move fluids.

The human gut also uses peristalsis — waves of involuntary constriction and relaxation of muscles — to mix gut contents and move them along.

Woods and colleagues made the discovery after an Antarctic mission to explore a phenomenon known as “polar gigantism”.

Scientists had long observed that polar species, including giant sea spiders, have larger bodies than their more temperate or tropical relatives.

The trend raised a lot of intriguing questions about how the polar species manage basic life processes, including how to get enough oxygen into their bodies.

“My ‘aha!’ moment was to consider that maybe all that sloshing of blood and guts was not about digestion but instead about moving respiratory gases around,” he said.

It’s not clear whether the sea spiders’ space-filling guts first arose for purely digestive functions and the respiratory benefits came later or vice versa, the study said.

“Respiratory gut peristalsis may be more widespread than previously recognized,” the researchers wrote in the paper.