Meet the ‘bunny rabbits’ of the sea

The sea bunny is one of the most interesting and adorable marine creatures in the ocean. But beneath the fluffy facade lurks an extremely toxic mollusc with super senses.

The adorable sea bunny captured the hearts of its native Japan after its discovery

The sea bunny, Jorunna parva, was first discovered off the coast of Japan in 2014. It became something of an internet sensation, particularly in Japan, when a video showing off its striking resemblance to a bunny rabbit went viral. However this tiny impostor is actually a sea slug, also known as nudibranchs, and apart from appearance couldn’t really be any further from its namesake. The mini-mollusc is actually quite common and can be found throughout the Indo-Pacific from Japan all the way down to South Africa. Whilst most of the images you see online will be a rabbit white colour it is actually far more likely that you will encounter an orange or yellow one in the wild. They very rarely grow larger than an inch in length making them even more adorable and one of the smallest nudibranchs. They are also quite short lived only surviving for a couple of months

Ears, tail and fur

Although the sea bunny shares a lot of its distinguishing traits with the cute household pet, their functions couldn’t be any different. It’s little ‘ears’ are actually rhinophores which are sensory organs that detect chemical scents in the water column. Therefore they are actually more like feathery tongues than actual ears. They help the bunnies locate their food and also their mates which they are very effective at doing over large distances. The black specks in its ‘fur’ are called caryophyllidia which are less understood but also believed to play a sensory role. Sea bunnies do not have any eyes or visual system and so rely solely on their ‘ears’ and ‘fur’ to navigate their surroundings. The bunny’s tail is in fact actually its gills and so it quite literally breathes through its backside.

Despite looking like a rabbit the sea bunny actually has no ears, fur or tail

A toxic taste

Unlike real rabbits the sea bunnies do not have to spend any time worrying about predators. Like all other sea slugs from the same group, known as dorids, the sea bunny incorporates the toxins from its prey into its own body making it deadly for any other mollusc or crustacean to eat them. They acquire the poison from various sea sponges and can only eat them thanks to a specialized digestive system that separates out the dangerous chemicals from the rest of the sponge. Some of the toxins isolated by sea bunnies may even have medicinal properties and are now also being trialled as cancer drugs.

The more common yellow sea bunny. Bright colourisation is an indication that it is toxic and should not be eaten

Mating un-like bunnies

The sea bunny like all nudibranchs are actually hermaphrodites meaning they have both male and female sex organs. They mate by both exchanging sperm with one another to fertilize their eggs. Therefore they are both mother to their own children and the father of someone else’s and both their offspring are direct siblings. They have relatively long copulatory spines which they spike into each other to keep them together like a tether until the exchange is complete. Because of their short lifespan and isolated behaviours mating is not guaranteed and must be taken advantage of when the opportunity arises. This is also why it is so important they have such a well-developed sensory system to be able to locate one another.

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