Skip to main content

The California Sea Hare


The Sea Slug or Sea Hare: A Laguna Beach Local

This is probably the world's first fan page devoted to the California sea hare. No, seriously. When I looked up A. californica online after finding a tidepool full of them, I discovered some fascinating facts about this unassuming animal. Not only does it switch sexes every other day during at least part of its life cycle; it's played an important role in Nobel Prize-winning research in neuroscience!

Not bad for a critter that doesn't even have a spinal cord.

On this page I'll share photos, videos, and basic information about the California Sea Hare, a large sluglike mollusk found snuffling about the tidepools off the coast of California. For beachcombers, tidepoolers and nature lovers, I hope I can give you some appreciation for an animal that doesn't have quite the star power of a clownfish (of Finding Nemo fame) or humpbacked whale. For marine biology students looking for more in-depth scientific information than my Sea Hare factsheet covers, check my links section below: I may not have the level of expertise you're looking for, but I've found a few sites that do!

Video: California Sea Hares - Tidepools at Laguna Beach in Orange County, CA

Sea hare video clips taken by me and my mother (Ann Brundige), 02.27.09.

They're oddly cute, aren't they? Although the hermit crab caught in the slow-motion hit-and-run in the first clip might dispute me, if it had higher brain functions.

All About California Sea Hares - Scientific Name: Aplysia californica


There's dozens of species of sea hares, sluglike marine animals found around the world. The California Sea Hare is a brown or reddish spotted species found all along the coast of California down into Baja.

  • Names: California Sea Hare, California Sea Slug, Aplysia californica
  • Size: Varies. A foot (30 cm) is typical for full-sized adults when stretched out. Those pictured here were closer to 5 to 8 inches.
  • Weight: According to this Aplysia Californica size chart, foot-long California Sea Hares are typically around 100 grams; the ones I saw were closer to 20 grams.
  • Diet: Unlike some sea hare species, Califonia Sea Hares are vegetarians! They eat Coralline Algae (brown or red algae), soft frilly stuff found in rocky tidepools during low tides. In other words, they fill the same role as aquarium fish used to clean up algae and keep tanks scum-free.
  • Color: Dark brown to reddish-brown, sometimes with a yellowish or pink cast, depending on the color of their food. Adults are mottled and well-camouflaged. Young juveniles are pinkish-orange and don't show mottling.
  • Anatomy: They're gastropods, from the Greek for "stomach-foot," which describes most of their body. They have a small bit of leathery shell inside, protecting some of their organs. They have a sucker-like mouth and a pair of small black eyes on the top of their head. But they do most of their tasting/smelling/sensing using their "rabbit ears," the pair of short tentacles behind their eyes that gives sea hares their common name. These tentacles are called "rhinophores." Sea hares use them not only to detect food but also enemies, their surroundings, and other sea hares. (They also have two more tentacle-like "toes" at the leading edge of their foot, on either side of the mouth, which can look like rabbit ears from above).
  • Lifespan: Usually a year. Here's a diagram with videos showing you the life cycle of sea hares at different ages.
  • Reproduction: California Sea Hares are hermaphrodites, meaning they have both male and female parts -- in fact they alternate being male or female on different days! Eggs hatch after 8 or 9 days into microscopic larva, which gradually grow into full-sized slugs, dining on other kinds of red algae as juveniles.
  • Habitat: Shallow tidepools with red algae in the "Low Tide Zone," only exposed during the lowest tides each month. In Orange County, I've noticed bright purple sea urchins during these especially low tides, so if you can see them, start hunting for sea hares in shallow pools with pinkish red algae. You'll also see blue mussels, hermit crabs, and sea anemones in the area (although these also live higher up, so they are not reliable indicators of sea slug habitat).
  • Fun Facts: This kind of animal has been called "sea hare" since antiquity, since some European species are markedly rabbit-shaped. The purple ink of one species was used by ancient scholars in Jerusalem to write sacred texts-- maybe even the Old Testament!

California Sea Hares: Nobel Prize Winners!

Helping Neuroscientists for Over Fifty Years

The nervous system is the "wiring" that makes our bodies work. It includes our brains. It just so happens that California Sea Hares have very simple nervous systems and very large neurons (nerve cells), making them perfect subjects for studying neurobiology!

A lot of what scientists now know about the human nervous system, neurons, reflexes, memory, and even complicated behavior like learning grew out of studies of Aplysia californica.

"In 2000, Dr. Eric Kandel won the Nobel Prize in Physiology or Medicine for his research in how neurons are able to form and store memories. For this award-winning research, he used Aplysia from Rosenstiel School's National Resource for Aplysia along with neurons from mice. Other studies of Aplysia have led to drugs now in clinical trial aimed at reversing memory loss in patients with degenerative mental diseases."

~ Source: Aplysia Center Website

In other words, drugs currently being tested to reverse Parkinson's Disease and Alzheimer's have been developed thanks to the humble California Sea Hare!


I'm not a marine biologist. In fact, when I saw these animals in tidepools at Laguna Beach, I didn't know anything about them except that they were sea hares! I Googled "sea hare" and studied a lot of photographs and descriptions on expert websites until I was sure I'd identified my slug. (A pity there's not much of a market for a Roger Tory Peterson Guide to Marine Invertebrates.)

Here's the websites where I found all my information.

  • "Aplysia californica" on the Sea Slug Forum
    The Sea Slug Forum, moderated by marine biologist Bill Rudman at the Australian Museum, is surprisingly fascinating, with lots of information and great pictures. Here's questions and answers submitted to Bill on the California Sea Hare.
  • Tidepool Ecology: Laguna Ocean Foundation
    All about the tidepools of Laguna Beach, with the types of animals and plants typically found there.
  • Tales from Our Tidepools, Treasures Beneath the Sea
    A lecture given by marine biologist Genny Anderson at UC Santa Barbara. Great introduction to tidepooling on the California coast. Near the end of the "Treasures Beneath the Sea" section are two amazing photos of California Sea Hares inking.
  • The Rosenstiel School: Aplysia Facility
    National Institute of Health facility where California Sea Hares are bred and used to study neurological diseases like Alzheimer's and Parkinson's. This incredibly detailed site tells you all about their biology, how to care for (and order!) them, an
Scroll to Continue

California Sea Hare, Laguna Beach

California Sea Hare, Laguna Beach

California Sea Hare, Laguna Beach

More Sea Hare Videos

Here's a couple more videos of sea hares by people with better cameras than mine!

© 2009 Ellen Brundige

Sea Hare Fan Mail

Ellen Brundige (author) from California on May 07, 2014:

@JohnGauman: EEK. Sorry, I didn't realize my guestbook was unmoderated. I will leave that comment up, along with yours. Folks, this page is about admiring and photographing wildlife, not harming it!

JohnGauman on May 07, 2014:

@anonymous: Also, in California (and other places, as well), marine invertebrates (and vertebrates!) are protected! You may not even remove them without a permit!

JohnGauman on May 07, 2014:

@terri-daskalakis: Yikes! These invertebrate animals are protected---and are ILLEGAL TO TAKE WITHOUT A PERMIT!

terri-daskalakis on January 12, 2014:

They taste great with garlic

anonymous on October 11, 2012:

You can come to the Newport Nautical Museum and touch a Sea Hare!

mouse1996 lm on August 21, 2012:

Great information. I've never heard of a sea hare before. They look so interesting. I'd like to see one in person some day.

anonymous on June 30, 2012:

Please know that you can not handle or touch any tidepool animals in Laguna Beach. You can observe all of them, but do not handle them. You will see large signs with the "Tidepool Rules" at the entrance to every beach.

RuralFloridaLiving on June 19, 2012:

Nice lens!

Ellen Brundige (author) from California on April 21, 2012:

@anonymous: Good heavens. I usually delete random links dropped on my pages, but those are very creative and funny! Good job, all of you!

Rose Jones on April 21, 2012:

Really fun lens. And BTW - I visited the three youtube videos (mentioned in the comment below) created by the graduate students about A.californica - very funny. I wish my biology teachers had been like that. I pinned your lens to a new board I created "Cool Critters"

anonymous on December 08, 2011:

Students in my Chemical Ecology class created scientific music videos and these premiered this morning at our 2nd Annual Chemical Ecology Filmfest. Three of the videos focus on A. californica research. Here are the links...


anonymous on November 25, 2011:

Really great, thanks! Helped me heaps while researching Sea hares.

anonymous on November 25, 2011:

Useful for my homework project. Thanks.

Jeanette from Australia on August 14, 2011:

They look so sweet! Just returning to add a little angel blessing and to let you know that this lens has been added to my animal alphabet lens.

Ellen Brundige (author) from California on May 11, 2011:

@anonymous: Oh, I will have to look up that visitor center!

MokaChocolate on May 11, 2011:

How cool! Thanks for introducing me to a new sea critter.

anonymous on April 11, 2011:


Barbara Walton from France on February 01, 2011:

What interesting photos, but anything less like a hare I can't imagine! Fascinating subject.

ShamanicShift on January 30, 2011:

This was a new critter for me -- and I'm circling back today to bestow a SquidAngel blessing!

Heidi Reina from USA on January 17, 2011:

I've seen them in tidal pools but never knew they were "sea hares". Great info, pics and videos. Blessed by a SquidAngel ~

Ellen Brundige (author) from California on January 10, 2011:

@ChemKnitsBlog2: Oh, wow, thanks! That was a fun page.

ChemKnitsBlog2 on January 10, 2011:

Thanks for identifying the unicornfish! I have featured this lens on my fish page.

VideoGameFanatic on January 08, 2011:

Never knew there was something called a sea hare. Thanks for creating this lens and letting us know.

anonymous on January 01, 2011:

Interesting creates, I hadn't heard of the California Sea Hare before. I like to go on site that show pictures of newly discovered living things. There are so many strange but wonderful creatures, I'm just in awe of them all. Creation is inspiring!

Joan Hall from Los Angeles on December 19, 2010:

Hi! I'm adding this to my Animal Instruction Lenses lensography.

Ellen Brundige (author) from California on September 20, 2010:

@eridqua: I really need to stop Squidooing and get out to the beach more. We're very lucky to live here. And sadly, the mess in the Gulf reminds me that something could happen -- you just never know.

Ellen Brundige (author) from California on September 20, 2010:

@percula lm: That's great! They're like living lava lamps, aren't they?

ShamanicShift on September 19, 2010:

Thanks for introducing me to a new, wondrous critter to consider! I have added this to my featured California lenses on my California_ lens.

percula lm on September 19, 2010:

I was just looking at one of your lenses and noticed you had a link to a sea hare lens, and here I am. I have been fascinated with marine life and marine biology since before I can remember. When I was around 20 years old I started in the reef tank world. I had reef tanks for about 8 years. I wanted to mention that sea hares are more and more common in the reef aquarium community. In fact I have had 1 in the past and some friends of mine have owned them too. They are interesting critters to watch, and very easy to keep as pets (as long as you keep the water quality up).

eridqua on September 17, 2010:

Haha. I'm delighted to know there's another person out there that knows what a sea hare is! I grew up here in SoCal and my dad is a major ocean/beach nut. From the time I was a baby he's been teaching me ocean terminology. We love to go explore the tide pools and enjoy the marine life there. Thanks for making this lens. Go sea hares!

Jeanette from Australia on September 09, 2010:

The ocean is so full of amazing creatures. We haven't gone scuba diving for a while now but it's like a completely different world under the water. These are certainly fascinating creatures.

Nan from London, UK on September 08, 2010:

These are fascinating little creatures. I could sit here and look at the photos over and over.

And is it a coincidence that the captcha is lookpod?


Ellen Brundige (author) from California on August 13, 2010:

@anonymous: I'm not a marine biologist, so I don't know for certain. But that marine biologist in video #5 did take a sea hare out for a while to show a class he was teaching.

I've been hunting around on the net trying to find an expert to ask, but unfortunately the sea slug forum is closed right now!

I would err on the side of caution -- hold them in shallow water to demonstrate, only take them out for a very brief time -- just to make sure. I'm not sure if they can breathe out of the water.

But I doubt they die instantly. Most marine animals can handle being out of the water for a short time, just as we can get by without breathing for a short time.

anonymous on August 11, 2010:

Can sea hares be taken out of the water for short periods of time, no more than 3-4 minutes? I run a sailing camp and there are a bunch of sea hares on the rocks by the dock, I pulled one out of the water, very carefully not to harm it or squash it, to show the kids, and someone mentioned that I had just killed it taking it out of the water for such a short period of time. Is this true?

makeamill on June 18, 2010:

you have a pretty neat article you should check out mine when you get a chance

anonymous on May 16, 2010:

We have one that lives out side our house along the dock. St. Georges Bermuda

Ellen Brundige (author) from California on May 02, 2010:

@nebby: Thanks for visiting! It just goes to show you that there may be unusual things right in our own back yards -- or right offshore.

nebby from USA on May 02, 2010:

This lens is fascinating - I had never heard of California Sea Hares before.

Ellen Brundige (author) from California on April 15, 2010:

@LabKittyDesign: Ack! No, that was Greekgeek's brain on the fritz. Thanks for catching it!

LabKittyDesign on March 01, 2010:

Cool lens! But is spinal "chord" a typo (or a Brit spelling)? Or is this a Nudibranchia thing?

Kathy McGraw from California on January 17, 2010:

I enjoy the tidepools at Swamis in Encinitas. There is so much to see, and your tips on using caution when handling are good. *Blessed* by an Angel

Ellen Brundige (author) from California on November 03, 2009:

[in reply to Joe] As long as you handled them gently, you probably saved them! They can't live out of the water too long. Don't worry about the ink -- the animal does that to say "put me down!" but it's not a sign of injury, just alarm. Good job!

anonymous on June 27, 2009:

I went to malibu today and I saw a bunch lying on the sand. Not sure if they were alive or dead but I ended up taking 4 of those back to the water. One was releasing a purple ink...

I hope I was able to save them.

Ellen Brundige (author) from California on March 31, 2009:

[in reply to kiwisoutback] Probably because they're in the pools that are only uncovered in an especially low tide. Basically, if you see that pink crunchy stuff (algae) and/or those lovely purple sea urchins, usually past the first banks of black mussels, you've hit the sea hare area. (Also look for the occasional massive, pudgy orange starfish on rocks.) Pools with just hermit crabs and sea anemones are uncovered by regular tides.

Kiwisoutback from Massachusetts on March 24, 2009:

Strange! I've never seen of these. I'm headed to Long Beach in May, I'll see if I can spot one. Thanks for the education!

Dianne Loomos on March 01, 2009:

I enjoyed reading about the sea hare. Lensrolled to my snail lens.

Ellen Brundige (author) from California on March 01, 2009:

[in reply to spirituality] Yep! Sea hares seem to have evolved from a primitive form of snail; the bit of shell that's left inside of them is vestigial, like an appendix.

religions7 on March 01, 2009:

A leathery shell? Must be an ancient type of snail then :)

Jimmie Quick from Memphis, TN, USA on February 28, 2009:

Quite a fascinating creature. You've dug out so many neat tidbits about this fellow. I like him!

The sea hare deserves a blessing as well. So, voila, there it is!

Related Articles