The Adorable Science Behind the 'Sea Bunny'

Meet the cutest sea slug ever.

White and speckled nudibranch known as a sea bunny.

Izuzuki Diver / Wikimedia Commons

It’s round, and fluffy and has wee wiggly ears. Sort of. These little sea creatures, affectionately dubbed “sea bunnies,” have become social media celebrities. They’re actually sea slugs, and belong to a taxonomical order called the nudibranchs, which is comprised of some 3,000 species.

Nudibranchs are shell-less marine mollusks who shed their shells in the larval stage. Their name means "having naked gills" (from nudi- for "naked" and the Latin "branchae" for gills), referring to their exposed breathing apparatuses.

Nudibranchs can be found in the shallow waters of oceans around the world. They have a regular feeding organ, with which they use for feeding on other invertebrates, with a special taste for sea anemones. They come in myraid shapes and sizes; some are large bottom creepers, while others are tiny with tentacles sprouting from their heads.

Nudibranchs are often wildly colored, with day-glow hues that look like they came straight from a Technicolor dream; think vivid purples, hot pinks, and fluorescent oranges. But some, like the sea bunny, make up for a lack of vibrancy with their cuteness.

The bunny slug species is Jorunna parva, and was first described by the renowned Japanese marine biologist Kikutaro Baba. The fluffy white sea bunnies are primarily found off the coast of Japan. Jorunna parva have also been found in the Indian Ocean and off the coasts of the Philippines.

As for the “ears”—over on Deep Sea News, Dr. Craig McClain explains that those are really rhinophores, organs that help the sea slug sense chemicals dissolved in the water and also detect changes in currents. “In the group of nudibranchs that contains the sea bunnies, the rhinophores are particularly 'fuzzy' allowing for more surface area for this reception to occur on.”

All nudibranchs are hermaphrodites, which means they produce both sperm and eggs but cannot fertilize themselves.

A Jorunna parva nudibranch portrait, Anilao, Philippines.
Portrait of a Jorunna parva. Anilao, Philippines.

Brook Peterson / Stocktrek Images / Getty Images

Jorunna parva have a number of different colorings and are often yellow with black specks and rhinophores. Some can even be a bit greenish. McClain points out that there is some debate in the scientific community over whether or not the different color variations represent separate species.

If there weren't enough reason to swoon over sea bunnies, the fact that these creatures are incredibly tiny adds extra points to their adorableness score. Jorunna parva are less than an inch in length.