In the coldest depths of the Arctic and Southern oceans are huge "sea spiders" with eight massive long legs and a proboscis, according to the Daily Mail. These "spiders" are actually considered pycnogonids, which are a type of primitive marine arthropod, and grow bigger in these polar oceans than anywhere else in the world, reaching sizes so big that they are considered to fall under polar gigantism, although scientists are baffled as to why.
Although sea spiders can be found all around the world, according to Hakai Magazine, nowhere else do they reach such massive sizes - typically, they are small creatures, whereas in Antarctica they can grow to a leg-span of almost 25 cm. Polar gigantism doesn't just affect sea spiders either; copepods, echinoderms and certain types of mollusks have also been found to reach larger sizes than average in the poles, according to Market Business News.
One team of researchers believes that a possible explanation for this increased size could be linked to the higher concentration of dissolved oxygen concentrations in cold water. Off the coast of Antarctica, oxygen content in seawater is higher than usual, and combined with slower metabolisms due to the cold temperatures, this may be one reason that the sea spiders developed polar gigantism.
In order to test their hypothesis, the resesarcers drilled into the depths of the Antarctic sea and collected sea spiders, which they then tested in various temperature conditions. So far, the results show that larger sea spiders fare worse in low-oxygen environments, supporting their hypothesis. However, further research will need to be conducted in order to determine if this is the definitive cause of polar gigantism in Antarctic sea spiders.