The tiny pyrosomes - known as "sea pickles" or "fire bodies" - are incredibly rare, even in coastal areas. So scientists are puzzled over what's going on in the United States' Pacific coastline, which is getting overrun with millions of the sea creature.

According to a report from The Guardian, this mysterious little animal - only a few millimeters long each - is also called the "unicorn of the sea" for its rarity. Now, millions have washed up on the beaches of the West Coast, getting tangled up on fishermen's nets and surprising local witnesses.

While the actual animal is miniscule, they do assemble in huge colonies. A report from National Geographic revealed that the jelly-like pyrosome is actually technically a colony of other multi-celled animals that are called zooids. While seldom seen, they're usually spotted in places like the Ivory Coast, Mediterranean Sea, Australia or Florida.

Beginning the past spring though, the strange creatures started flocking to the eastern Pacific - from Oregon to Alaska - in great numbers. In one account, a single research net swept up 60,000 in just five minutes.

The sea pickles might just be a peculiar oddity for many locals, but they cause considerable trouble for fishermen who are unable to catch anything because of the tightly packed clusters congesting their nets and hooks.

"Right now we are scrambling to learn as much as possible while we have the opportunity," University of Oregon graduate student Olivia Blondheim, who is part of the research team studying the unusual phenomenon, told The Guardian. "If we continue to see this many, what impact will it have on the ecosystems here, and what economic impact on the fisheries? There are so many unknowns at this point, it really is a remarkable bloom."

One of the potential negative effects is that the deaths of these animals may suck massive amounts of oxygen from coastal seas, which can be destructive to other marine life.