Posted by: Rob Viens | May 6, 2012

Darwin and the Sea Bunnies

Okay – to be fair on May 6th Darwin actually described a sea hare (not a sea bunny)  in his Zoological Journal. Sea hares are actually just a type of sea slug  – not really at all like a cute little fuzzy bunny (though some might argue that they are still cute.)

Darwin’s single entry in his diary for May 5/6 notes that the days had been wet and soggy:

“These days have quietly glided away; there have been torrents of rain, & the fields are quite soaked with water; if I had wished to walk it would have been very disagreeable” (May 5/6)

But he did seem to get out to the tide pools for a little while, for he includes a description of a little sea hare dated today in his zoological notes. He refers to the specimen as a Aplysia (which is a genus within the family of sea hares known as the Aplysiidae).  All sea hares, in turn, are a type of sea slug – a snail (gastropod) without a shell (though some have a modified internal shell).  For completeness – they belong to the Mollusca family – along with clams, mussels, oysters, octopi, snails, squids, etc.

Aplysia californica (from Wikipedia Commons)

Aplysia californica

Darwin has a fairly detailed description of his sea hare including the following:

General Description and Size –

“Animal with lateral crests unequal; right side nearly orbicular. very large.— measured internally to the back 2 & 3/4 inches wide… crests extend nearly length of whole body…foot broard, length when contracted 4 & ½ inches, I have no doubt when crawling would be 6 inches. (Zoological Journal)

Color –

“…colour, purplish dark brown with whitish marking, & in them minute snow white dots about 1/48th of inch in diameter.— on the edge of crests their markings are larger & more distinct.— Feelers same colour…Mantle purplish, posteriorly forming simple tube … When first taken emitted a little purple…” (Zoological Journal)

Swimming –

“…If the Aplysia uses its lateral crests to swim.— Can this?” (Zoological Journal)

Aplysia faciata (from the Sea Slug Forum)

Aplysia faciata

From what I can tell, this description seems to fit (pretty well) with that of the “Brazilian sea hare” formerly known as Aplysia brasilliana.  Recent studies suggest, however,  that this Brazilian “species” is actually just a local population of the species Aplysia faciata (the mottled sea hare) which is found throughout the Atlantic.

A couple additional reflections on Darwin’s description:

(1)  The lateral crests that he describes are called parapodia, which are common on many Aplysia (though in some cases they are fused together).

Parapodia and rhinophores of an Aplysia dactylomela (from the Sea Slug Forum)

Aplysia dacylomela

(2) The other feature common to the sea hare are the two large rhinophores found on the head (that sort of look like the ears of a rabbit – hence the name sea hare). These rhinophores are sensing organs, allowing the Aplysia to detect chemical “scents” in the water.

(3) Some sea hares can use their parapodia to swim. By flapping them, they can virtually “fly” through the water. And surprisingly, they are quite beautiful swimmers.

Aplysia faciata swimming (posted by tinet07 to YouTube):

(4) Most sea hares have the ability to secrete a purplish ink to help protect them from predators. Some also accumulate toxins from the food they eat in their skin, making themselves toxic (or a least bad tasting).

I think next year our house will have a visit from the Easter Sea Hare – with all this wonderful diversity why restrict ourselves to a mere bunny? (RJV)

PS – For everything you could ever want to know about sea hares and other forms of sea slugs, be sure to visit the Sea Slug Forum. They really are quite beautiful.

PSS – Darwin also saw Aplysia in the Cape Verde Islands (see Colorful Corals and Cuttlefish).


  1. I’m sorry but any post about Aplysia without mention of their reproductive habits is disappointing to say the least! Well, perhaps you are trying to keep this a ‘family-freindly’ blog…..Sea Slug Forum is an awesome resource and for details and a photo or two you might try-

    • Thanks! I just try to pace myself a little since Darwin mentions these guys several times. He found this one half dead on the beach – so I suspect he did not get a chance to observe such “activity”. You’ll have to share sometime…

  2. […] and have several similar characteristics. (See some of Darwin’s encounters with sea slugs in Darwin and the Sea Bunnies and Purple Snails and Blue Slugs.) They are all basically snails without  shells, though the land […]

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