Marine biologists say the spooky "Cascade Creature" seen drifting through the deep sea in a viral video isn't a whale placenta, a parachute, a plastic bag or an alien visitor: It's a type of jellyfish known as a Deepstaria enigmatica.

The video, which was apparently captured by a remotely operated vehicle near an underwater drilling site, caused a bit of a stir over the past couple of weeks among weird-science fans. Now it looks as if the truth is out there, thanks to assessments from experts such as Steven Haddock at the Monterey Bay Aquarium Research Institute and Craig McClain at the National Evolutionary Synthesis Center.

"This bag-like jelly is not that rare, but is large, so rarely seen intact," Haddock and his colleagues write on the JellyWatch Facebook page. "In the video, the swirling from the sub makes the medusa appear to undulate, and it even turns inside-out." They provide a helpful picture of a more typical specimen.

McClain is even more helpful in his posting at Deep Sea News. He provides citations on previous sightings of the beast, including explanations for the jellyfish's weirdly collapsed shape. And he shows through photographs and drawings that the strange appendage and whitish lumps seen in the video are D. enigmatica's gonads. TMI, Craig ... TMI.

For a third opinion, look no further than Australia's Nine News, which quotes Daniel Bucher, a marine biologist at Southern Cross University, as saying that the gonads were the giveaway.

Now that we've settled that, bring on the next sea monster.

More sea monsters:

• Iceland's monster unmasked
• Monster bug? It's no joke!
• Nessie-like monster filmed in Alaska
• Why giant squid have basketball eyes
• Fishermen pick up dying giant squid

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.