A rare black jellyfish was found off the coast of La Jolla in San Diego by a kayaker. What was special about the jellyfish was its size. It was the size of a hula hoop.

While fishing the kelp beds in his kayak about a quarter of a mile off La Jolla's shore on Friday, July 1, Joe Richman saw a big black jellyfish swimming right beside him.

In 30 years of diving and fishing off San Diego, I've seen a lot of cool things and this ranks up there as one of them, cbs8 quoted Richardson as saying.

Richman suspected that it was a rare black jellyfish. It was further confirmed by Aquarist Vince Levesque with the Birch Aquarium that what Richman saw was in fact a black jellyfish.

A black jellyfish can be up to three feet wide and its trailing tentacles can be 30 feet long. Black jellyfishe are named for the dark maroon color of an adult's belly.

In July last year, floating black jellyfish were spotted in San Diego Bay. According to Nigella Hillgarth, executive director of Birch Aquarium at ScrippsInstitution of Oceanography, said approximately a dozen black jellies had washed ashore at Shelter Island. Some of them were as large as the lid of a trash can.

Until 1997, this mysterious species was not officially described in scientific literature. Hillgarth said the life cycle of black jellyfish is not fully known by scientists yet.

Since 2005, black jellyfish have been reportedly seen at least three times. However, the reason why sightings of black jellyfish have increased in recent years in San Diego County is still unknown, Hillgarth said.

Few days back, a nuclear reactor in Japan was forced to shut down due to infiltration of enormous swarms of jellyfish near the power plant.

A similar incident was also reported recently in Israel when millions of jellyfish clogged down the sea-water cooling system of the power plant.

Such massive invasions of the species have raised speculations and scientists are trying to figure out the reason behind such unusual growing trends.

Check out the pictures and video of the rare species below.