Raleigh, N.C. — It's reminiscent of something from the 1958 science-fiction film, "The Blob" – a beating, pulsating, mysterious, slimy mass that has grabbed widespread attention across the Internet.

And it's growing and living in the sewer below Cameron Village in Raleigh.

A 2-minute video of the clusters, taken in April, was posted onto YouTube a few weeks ago and has quickly made its way onto other social networking Web sites. The broadcast industry publication TV Week ranked it Wednesday as the No. 1 viral video on the Web.

Speculation on YouTube as to what it might be ranges from a marketing ploy to promote a new alien movie to undocumented life form to a sewer monster.

But a sewer monster, it is not.

The city of Raleigh says the video – of a 6-inch sanitary sewer line – was taken in April during an inspection of a privately maintained sewer line in Cameron Village.

Ed Buchan, an environmental coordinator with the city's Public Utilities Department, says the mass is believed to be tubifex worms, which form clusters or colonies of about a half-inch to 1-inch in diameter.

Also known as "sludge worms," they are normally found in sediment of ponds and are sold as fish food in both live and dried forms.

Thomas Kwak, a biology professor at North Carolina State University's Cooperative Fish and Wildlife Research Unit, however, says the so-called monster is actually a cluster of invertebrates called bryozoan, which are commonly found in both the sea and fresh water environments.

It's unclear how they got into the sewer system, but Kwak said it isn't surprising. The bryozoan feed off bacteria and thrive in cold, dark environments. Those in the video are smaller than a fist, but could grow as large as a watermelon, he said.

"These organisms are completely harmless," Kwak said. "It's another interesting aspect of nature that we don’t' get to see every day."

Buchan says that because the worm-like creatures don't pose a threat to the city's water quality, the city isn't requiring York Properties, which manages the system and Cameron Village, to remove them.

York did not return calls seeking comment, and it's unclear if it plans to remove the colonies.