A-z - Animals

Sea Hare: 3 Facts You Won't Believe

Keep reading to watch this amazing video

key point:
  • Native to coastal waters between the Indian Ocean and the central Pacific Ocean, the sea slug is a cute, furry marine slug that resembles a rabbit. They are diverse creatures that can take on all sorts of fantastic forms, dazzling colors and peculiar features.
  • The sea hare is thought to start its life in a shell that is discarded before reaching adulthood. Its coat is made of tiny rods called carnations, some of which end in black knobs that give it a speckled appearance. Its two long tentacles, called rhinoceros, look like rabbit ears. The sea hare's gills are located on the back of the sea cucumber, similar to a tail.
  • Aplysias are born hermaphrodites and are able to produce sperm and egg cells inside their bodies. They still have to find a mate to fertilize their eggs in order to reproduce. Every parent is always the mother of his own children, but the father of other people's children.

The sea hare, scientifically known as Jorunna parva , is a soft-bodied, shellless, marine-based sea cucumber. Although Japanese zoologist Kikutaro Baba first described these cute, furry, wiggly little sea creatures in the 1930s, their popularity on social media rose when people started noticing their striking resemblance to rabbits. They are less than an inch long and are native to coastal waters between the Indian Ocean and the central Pacific Ocean. Its conservation status is unknown, but it is presumably common.

Sea slugs belong to a taxonomic order of sea slugs called nudibranchs (itself a gastropod), and they come in a variety of striking colors, odd shapes, and odd outfits. These are incredibly diverse creatures. Some sea cucumbers move slowly across the ocean floor in search of prey, while others swim across the surface in undulating motions.

The nudibranch itself varies between several different colors, including white, yellow, brown and, less commonly, green. There is some scientific debate about whether these variations represent entirely different species or simply color morphs of the same species. The rabbit-like white and black morphs seem to live mainly around Japanese coastal waters. The rabbit-like gastropods are found in Papua New Guinea, the Philippines, Reunion Island, Seychelles and Tanzania.

Like other slugs, the sea hare is thought to start its life with a shell, then shed it sometime before reaching adulthood. Any actual resemblance to the rabbit, including the white body and long "ears," is purely coincidental, but its appearance is striking nonetheless. The coat is actually made up of tiny rods called carnations, some of which have black knobs at the ends, giving it a speckled appearance. The "ears" are two long antennae, called rhinoceros, with small flaps on either side.

Read more  Coyote Predators: What Do Coyotes Eat?

Another important feature is the gills of the sea hare. They are located on the back of the slug rather than the front, sticking out like a tail. This is a distinctive feature of nudibranchs called dorids. In fact, the word nudibranch literally means nudibranch. While many aspects of the sea slug's physical characteristics and behavior remain a mystery, the sea slug remains a fascinating creature for scientific study and general interest.

#3. The body of the sea hare is basically one big sensory apparatus

sea hare
A nudibranch on a mossy rock. The "ears" of sea hares are actually sensory organs.

©Nual K/Shutterstock.com

As mentioned earlier, the nudibranch is covered in various sensory organs that help it navigate the water. The arrangement of the two antennae-like rhinoceros emerging from the head maximizes the surface area for the sensory receptors. Despite being composed of skin and nerves rather than fur, they appear extra thick and furry, like rabbit ears. These antenna-like structures are used to detect chemicals in the water and the direction of water flow.

The caryophyllales, which cover the body like fur, are also thought to perform some sort of sensory function, though how that is unclear. Given their density around the body, they must be very important to the slug's survival. Combined, they are the main way the slug senses its environment. Slugs have very limited other senses. Eyes can only see light and darkness, nothing else.

#2. sea hares are hermaphrodites

Hermaphrodites, meaning the presence of both male and female sex organs in one entity, are very rare as the primary mode of reproduction in vertebrates. Most reptiles, mammals, birds, etc. have a definite gender.

But gastropods, the sea hare among them, are different. They are hermaphrodites by nature and are able to produce sperm and egg cells inside their bodies. However, this does not mean that sea slugs are capable of self-fertilization. They still copulate sexually by exchanging sperm with another member of the species to fertilize their own eggs. If you think relationships are intricate, the sea hare's family dynamic trumps it. Every parent is always the mother of his own children, but the father of other people's children.

Read more  Cockroach Boric Acid: How Effective Is It?

The hermaphrodite reproductive strategy is very common among gastropods and other invertebrates, which must have provided them with some advantage. One possible theory is that it arose due to limited mate selection for slow-moving, immobile animals such as slugs and snails. Therefore, it is very advantageous to mate with anyone the sea hare meets without worrying about the sex of the other person. But the downside of this strategy is that sea slugs also need to expend a lot of extra energy, because it's actually quite expensive to keep producing egg and sperm cells throughout their lifetime.

We don't actually know many details about the mating process of the sea slug, but it's thought to perform a short courtship dance followed by the actual copulation for a few minutes. The nudibranch has a long spine that penetrates its mate, so the two stay connected until the sperm exchange is over. This is considered as painful as it sounds.

All mating opportunities are concentrated in the short life cycle of sea hares, which may last from a few months to a year. This means that nudibranchs must mature quickly and breed as often as possible. Their well-developed sense organs help them locate other sea hares in the wild. Unfortunately, their social behavior is also not well understood in terms of the extent of their existence.

sea hare
The nudibranch is a species of sea slug called Jorunna parva. Most are less than an inch (2.5 cm) long and are found throughout the Indo-Pacific from South Africa to the central Pacific.

© sutapat.t/Shutterstock.com

#1. Aplysia has a strong toxin that may have some benefits in cancer treatment

After losing its protective shell early in its life cycle, the sea hare has only one defense mechanism to keep it from being eaten. Fortunately, it's a very good toxin: a potent toxin called macrolide B. What's particularly interesting is that sea slugs don't produce this toxin themselves. Instead, it acquires the toxin by consuming the sponge during its natural feeding process. Sea slugs are apparently immune to the toxin, but predators are not.

Read more  10 Amazing Mountains in Georgia

Once the unpleasant experience of eating a nudibranch is made, a predator will think twice. Fortunately, this toxin may have interesting pharmacological applications. Scientists already know it has an unusual ability to limit the spread of cancer cells in the body. So far, this has limited clinical application. Scientists are still trying to figure out how to use these toxins to develop effective drugs to prevent cancer from metastasizing throughout the body.

Are sea hares good pets?

While some saltwater aquarium owners attempt to keep several species of nudibranchs as pets, this is a very challenging task and is only recommended for experienced aquarists. The reason is that sea slugs have big appetites, and they need a very limited variety of prey. Unfortunately, it's easy to inadvertently starve them to death. As far as nudibranchs are concerned, they are not approved as pets because they are poisonous and a threat to other creatures in the aquarium habitat.


Sea hares may bear a slight resemblance to rabbits, but that's where the resemblance ends. These are saltwater sea cucumbers that prey on other sea life, especially sponges. Considering that their diet of sea sponges also makes them poisonous to other animals, you definitely don't want to try cuddling with nudibranchs. These toxins may one day play a role in the fight against cancer, but that's a long way off. These adorable critters are best kept to themselves and enjoyed from a distance.

Sea hare attributes:

1. highly toxic
2. hermaphrodite
3. covered by sensory organs


  • 10 Incredible Slug Facts Learn all sorts of interesting facts about slugs in this inspiring article.
  • Slugs vs. Snails: 3 Key Differences Explained You might think that the only difference between a slug and a snail is that they don't have a shell. Read on to learn all the differences.
  • Are Spiders Insects? It's easy to mistake spiders for insects, but there are some key differences.

More from AZ Animals

featured image

sea hare
sea hare

© phiseksit/Shutterstock.com

about the author

Krishna is a lifelong animal owner and advocate. She owns and operates a small farm in upstate New York where she lives with three dogs, four donkeys, a mule and a cat. She holds a BA in Agricultural Technology and has extensive experience in animal health and welfare. When not working with her own animals and tending her farm, Krishna is helping other animal owners with behavior or management issues and teaching regenerative farming practices to nearby farmers.

Thanks for reading! Have some feedback for us? Contact the 10hunting.com editorial team.