Most creatures on this planet use their hearts to pump blood through the body, but not the sea spider — it uses guts located in its legs.

To be fair, at least the creature's anatomy matches its Lovecraftian appearance. Maybe we just have a weak stomach, but we're pretty sure this thing will haunt our nightmares for the next several days. Either way, enough of our nightmares and on to the science.

Guts Instead Of Hearts

Like other types of arachnids, the sea spider does have a heart, but it is too weak to function properly. This got some people wondering just how the creatures managed to pump blood throughout their bodies. Thanks to a team of researchers led by Arthur Wood of University of Montana, Missoula, we now know that the pump blood via guts contained in their legs. 

"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," says Woods."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 genesis of this study began in an Artic expedition focused on polar gigantism, which refers to phenomena of creatures that are native to the Artic being larger than their counterparts in more temperate climates. Most of these creatures are smaller than a human's nail, but some of the polar varieties can grow to be the size of a person's fist or larger.  It was during this polar expedition that Woods began to wonder how the various species of sea spider managed to pump enough blood to maintain life.

The exact reason these spiders work like this is unknown, but there are a couple of theories about why they work the way that they do.The first is that it saves energy by allowing the guts to handle the circulation of both food and blood. The second possible benefit ties into the way these spiders take in oxygen. Unlike fish, they do not have gills so they absorb oxygen via a diffusion process that takes place within their legs. Since the gut cavities are also located within the legs, it makes it easier for oxygen to circulate throughout the creature's body. 

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