California sea slug

The California sea slug (Aplysia californica) is also commonly called the California sea hare, and this is because the shape of all Aplysia species is reminiscent of the shape of a rabbit or hare. Sea hares (family Aplysiidae) are a kind of shell-less sea snail, a marine opisthobranch gastropod mollusk. This particular species lives in California and northern Mexico.

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The California sea hare can be very large, the maximum recorded length of being 75 cm (30 inches) when crawling and thus fully extended. Most adult specimens are half or less than half that size. A closely related species, Aplysia vaccaria, the black sea hare, can be even larger still.

Like all Aplysia species, the California sea hare is herbivorous. Its diet consists primarily of red and brown seaweed, which gives the animal its typically dark coloration. When it is considerably disturbed, as shown in the photograph on the right, the sea hare is capable of releasing reddish-purple ink (much like an octopus does) from a gland in its mantle cavity.

Life cycle

Like all sea hares, the California sea hare is hermaphroditic, acting as male and female simultaneously during mating. The eggs are yellow, but after 8 to 9 days change into a brown color before hatching into larvae. When this annual animal is laying eggs, it has reached the end of its life. Its lifetime depends somewhat on the temperature of the water: 14-25 degrees Celsius is best, but a somewhat cooler temperature delays spawning and extends its life somewhat.

Laboratory use

Aplysia californica has become a valuable laboratory animal, used in studies of the neurobiology of learning and memory, and is especially associated with the work of Nobel Laureate Eric Kandel. Its ubiquity in synaptic plasticity studies can be attributed to its simple nervous system, consisting of just a few thousand large, easily-identified neurons. Despite its seemingly simple nervous system, however, Aplysia californica is capable of a variety of non-associative and associative learning tasks, including sensitization, habituation, and classical and operant conditioning. Study typically involves a reduced preparation of the gill and siphon withdrawal reflex.

References

• NIH/University of Miami National Resource for Aplysia Facility