This squid swimming with her undulating egg sack is a sight to behold

This video of a mama Gonatus onyx (black-eyed) squid swimming while carrying her enormous egg mass is mesmerizing. Live Science explains that the black-eyed squid is one of the few squids that are known to brood their eggs, and this one is doing it with amazing grace and style as it undulates and shimmers through the water. Live Science describes the squid as "trailing its cargo of eggs like a long gown and flapping the fins protruding from its head to move through the water." I am absolutely, completely enraptured!

Live Science explains that before 2001, marine biologists had mistakenly assumed that black-eyed squid lay eggs on the seafloor, leaving them to "develop and hatch independently." Brad Seibal, who was working as a postdoctoral fellow at the Monterey Bay Aquarium Research Institute in 2001, discovered that marine biologists had it all wrong, however!

Live Science describes his discovery:

Seibal observed a black-eyed squid brooding an egg sack in Monterey Canyon, off the coast of California, through the lens of a remotely operated submersible.

"I just remember jumping out of my seat," Seibel, now a professor of biological oceanography at the University of South Florida, told Science Friday in 2016.

In a 2005 study, Seibel and colleagues described the brooding behavior of G. onyx females, which carry up to 3,000 eggs through open water until the young hatch and swim away. The squid use their arms to pump fresh water through the egg mass, which may help keep them supplied with oxygen. 

I wholeheartedly agree with the person who commented, "This is the coolest thing I've seen in a long time."

Previously:
How To: Harvest your own squid ink