The itsy-bitsy spider is not so itsy-bitsy anymore. Or at least, its counterpart under the sea isn't.

With a bright orange body, eight gangling legs, and an elongated proboscis, the sea spider prefers to lurk in the cold waters of both the Antarctic and Arctic oceans. Under these dark waters, the sea spider grows massive, with each of its eight legs sprouting to span the width of a person's face.

Known as pycnogonids, these creatures are part of a type of primitive marine arthropods, some of which are now extinct. Modern marine arthropods include crabs, shrimp, and lobsters.

Technically, pycnogonids are not true spiders or arachnids, but their classification as chelicerates somehow place them closer to one another.

Are Pycnogonids Becoming Mutant Spiders? No One Knows - Yet

Pycnogonids are usually small and cryptic. Because of their thin legs and diminutive size, these sea spiders need no respiratory system. Their proboscis allows them to suck out nutrients from invertebrates.

However, tiny sea spiders in Antarctica have somehow gotten bigger, growing up to 25 centimeters or 9 inches. Scientists say the growth is due to the phenomenon called "polar gigantism."

Strangely enough, pycnogonids are not the only ones that grow into unusual sizes. Echinoderms, copepods, and certain mollusks have all grown larger than their equatorial relatives.

The occurrence is a mystery for scientists. Multiple hypotheses have attempted to explain why and how polar gigantism happens, but none of these have been proven yet.

Cracking The Polar Puzzle

A team of researchers from the National Science Foundation, the University of Montana, the University of Hawaii at Manoa, and the United States Antarctic Program believe that by studying and examining Antarctic pycnogonids, the answer to this strange phenomenon may be unraveled.

Scientists drilled a hole in the thick Antarctic sea ice in order to collect some sea spiders. Two dry-suited and insulated SCUBA divers went into the water.

Art Woods, one of the members of the team, said the atmosphere surrounding the hole was pleasant, except that they were also freezing to death. The temperature of the sea water was around -1.5 degrees Celsius (29.3 degrees Fahrenheit) to -1.8 degrees Celsius (28.76 degrees Fahrenheit), the freezing point.

These extremely chilling temperatures may actually play a role in polar gigantism, scientists said.

Colder water can hold more dissolved oxygen than warm water, and the oxygen content of the coastal Antarctic sea is significantly high. Colder levels of temperature slow the metabolisms of cold-blooded animals. Reduced metabolism indicated less oxygen consumption.

Combine these factors and you may get supersized sea spiders. With their lack of a respiratory system, these marine arthropods depend on simple diffusion to get oxygen into their bodies. Woods explained that this will not work on organisms with large bodies unless the amount of oxygen available is vast.

The team of scientists tested how differences in temperature and dissolved oxygen content in seawater affected the physiology of Antarctic pycnogonids.

So far into their study, Woods and his colleagues found that larger sea spiders find it difficult to get by on seawater with low oxygen content. This evidence supports their hypothesis that abundant levels of oxygen influence the growth of these creatures.

Possible Implications

Scientists have yet to find the root cause for polar gigantism. Nevertheless, if seawater with copious levels of oxygen is essential for the survival of large marine animals, the implications of warmer oceans and decreasing levels of oxygen may be devastating.

The demise of gigantic sea spiders may not be noticeable because they live in the polar regions, but experts believe that king crabs, jumbo lobsters and other marine creatures are in danger of meeting their ultimate end.

Watch the video of the drilling expedition below.