Are “Sea Bunnies” really cute?

The blue seabunny later in the movie is a different species.

Lately, the sea bunny, which is a nudibranch (sea slug) called Jorunna parva, went viral on the internet. This due to its fluffy appearance with bunny ears and all. However, they might be hiding some peculiar things underneath this fluffy appearance. See this excerpt from a paper dealing with the phylogeny (description of the relations between species of a group) of this group of sea slugs:

The main features of the genus include a dorsum covered with caryophyllidia, low rhinophoral and branchial sheaths, a massive prostate with two sections, an unarmed vagina, a penis occasionally with hooks, an accessory gland with a spine, a labial cuticle (either smooth or with jaw elements), inner and lateral hamate radular teeth, and outermost teeth either smooth or denticulate (Valdés and Gosliner, 2001).

It all sound rather technical, but a few things stand out. Nudibranch are hermaphroditic, which means that they have both male and female genitalia. An unarmed vagina is, I guess, therefore pleasant for all individuals. But a penis with hooks? Luckily, this feature is reserved for other members of this group because J. parva doesn’t have penile hooks (Camacho-García 2008). They do have a copulatory spine, which is stabbed into their partner to hold on to each other during sex. I don’t know about you, but sea slug sex sure doesn’t sound like fun to me.

Picture from
Picture from Crawl Ray.

Showing your true colors

Above, you can see the sea bunny the way it went viral, all white and fluffy with bunny ears. However, most are brownish as in the picture below. I admit it, it does look cuter in white. The sea bunny is covered by tiny rods called caryophyllidia. Although it is unknown what the function of these are, it is certain that the “ears” are used for sensing their environment to find food and mates.

Picture from (Camacho-García 2008).
Picture from (Camacho-García 2008).

A poisonous beauty

Although it looks very cute, this sea bunny is very very toxic. It extracts these toxic compounds from the sponges it eats. So it doesn’t have to worry about being eaten. So is this little “sea bunny” really cute? Yes, as long as you don’t think about what it does “under the sheets” it is a beautiful fluffy sponge eating little slug.


Camacho-García, Y.E. and Gosliner, T. (2008) Systematic revision of Jorunna Bergh, 1876 (Nudibranchia: Discodorididae) with morphological phylogenetic analysis. Journal of Molluscan Studies 74: 143-181.

Valdés, A. and Gosliner, T. (2001) Systematics and phylogeny of the caryophyllidia-bearing dorids (Mollusca, Nudibranchia, Anthobranchia). Journal of the Linnean Society. 136: 535-636.About author