The California sea hare (''Aplysia californica'') is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

sea slug Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary t ...

in the sea hare family,

Aplysiidae Aplysiidae is the only family in the superfamily Aplysioidea, within the clade Anaspidea. These animals are commonly called sea hares because, unlike most sea slugs, they are often quite large, and when they are underwater, their rounded body sh ...

.Rosenberg, G.; Bouchet, P. (2011). Aplysia californica J. G. Cooper, 1863. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=240765 on 2012-03-31 It is found in the Pacific Ocean, off the coast of

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

in the United States and northwestern Mexico.

Distribution

''A. californica'' is found along the coast of California, United States, and northwestern Mexico (including the

Gulf of California The Gulf of California ( es, Golfo de California), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Bermejo''), is a marginal sea of the Pacific Ocean that separates the Baja Ca ...

). ''Aplysia'' species inhabit the

photic zone The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...

to graze on algae, mainly the intertidal, usually not deeper than .

Description

The maximum length recorded for the California sea hare is when crawling, thus fully extended, although most adult specimens are half this size or smaller. Adult animals can weigh up to . A closely related species, ''

Aplysia vaccaria ''Aplysia vaccaria'', also known as the black sea hare and California black sea hare, is a species of extremely large sea slug, a marine, opisthobranch, gastropod mollusk in the family Aplysiidae.Bouchet, P. (2011). Aplysia vaccaria Winkler, ...

'', the black sea hare, can grow to be larger still. A California sea hare is typically reddish-brown to greenish-brown, but the color varies based on the algae it ingests. Each sea hare houses four tentacles, with two on the head sheltering the eyes, and two on the face surrounding the mouth. The body has two folds, called parapodia, which envelop the gills for protection but enable water to get by. Below the body is a muscle that allows for mobility, almost like a foot. The California sea hare also has an internal shell to protect its organs.

Lifecycle

Like all sea hares, the California sea hare is

hermaphroditic In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have separ ...

, acting as male and female simultaneously during

mating In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. ''Copulation'' is the union of the sex organs of two sexually reproduc ...

. ''A. californica'' is known to form mating chains with up to 20 animals. The eggs are yellow-green, and change after 8–9 days into a brown color before

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e hatch. Mating is most prominent during the summer following the rise of the water temperature to 17 °C. ''A. californica'' has a generation time of 19 weeks: Days 1-37 after hatching from the egg comprise the planktonic stage, days 34-37 are the metamorphic stage, and days 45-80 are the juvenile stage. At about day 30, the larvae move on from the planktonic stage and begin to roost on algae, typically red algae. The larvae eat enough to double their weight every 10 days for the following 3 months while they undergo metamorphosis. Reproductive maturity is reached 85 days after hatching (133 days after deposition of the fertilized eggs). The development of the nervous system lasts for 140 days.Kandel, Eric Behavioral biology of ''Aplysia''. W.H. Freeman and Co., San Francisco. Often times, the California sea hare dies shortly after laying eggs. Cooler temperatures (14-25° C, or 57-77° F) delay spawning and have been shown to extend the lifespan.

Sexual reproduction

At the base of the right anterior tentacle is the aperture from which the penis can protrude. The genital aperture lies at the anterior end of the mantle cavity, a seminal grove arises from it and runs forward to the penis, at the base of the anterior tentacle. Coupling lasts for hours or sometimes for days, although the actual passage of the sperm may take only a few minutes. Egg laying normally has to be triggered by copulation, but it occurs spontaneously in individuals kept in isolation for up to 3–4 months (typically these eggs are unfertilized). Copulation occurs most frequently in the early morning, and only rarely after 12:30 pm. An individual animal weighing 2,600g was recorded to have laid about 500 million eggs at 27 separate times during less than five months.

Feeding habits

Like all ''Aplysia'' species, the California sea hare is

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

. Its diet consists primarily of

red algae Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

such as ''Laurencia pacifica'', ''Plocamium pacificum'', and ''Ceramium eatonianum'', which give the animal its typically reddish or pinkish coloration. Some California sea hares will appear more brown, which helps them blend into their surroundings. ''A. californica'' resembles the food on which it grazes, and cannot be distinguished easily from the seaweed unless the animal is moving. When the sea hares eat algae, they consume toxins, which they store in themselves to repel predators. They can also release these toxins as a purple ink, which will also discourage predators from attacking them.

Predators

Because of the toxins in its body that come from consuming algae, the California sea hare has very few predators. Predators include starfish, lobsters, and the ophistobranch ''

Navanax inermis ''Navanax inermis'', common name the California aglaja, is a large species of predatory sea slug, a marine opisthobranch gastropod mollusk in the family Aglajidae. ''Navanax'' is not a nudibranch, even though it somewhat resembles one; it belo ...

'' which will take juveniles. When it is considerably disturbed, the sea hare is capable of releasing two different kinds of ink from different locations within its mantle cavity, much in the way an octopus does. One ink is reddish-purple and comes from what is called the purple ink gland, while the other is milky white, comes from what is called the opaline gland, and contains the aversive chemical opaline.

Protective mechanisms

Inking provides protection from

spiny lobster Spiny lobsters, also known as langustas, langouste, or rock lobsters, are a family (Palinuridae) of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are also, especially in Australia, New Zealand, Ireland, So ...

s, a major predator of sea hares, by means of three mechanisms: chemical deterrence, sensory disruption, and

phagomimicry Phagomimicry is a defensive behaviour of sea hares, in which the animal ejects a mixture of chemicals, which mimic food, and overwhelm the senses of their predator, giving the sea hare a chance to escape. The typical defence response of the sea har ...

. The typical defence response of the sea hare to a predator is the release of chemicals such as free amino acids, ink from the ink gland, and opaline from the opaline gland. Chemical deterrence involves the release of toxic chemicals that are noxious to predators and rapidly dissuades them from feeding. Ink creates a dark, diffuse cloud in the water that disrupts the sensory perception of the predator by acting as a screen or decoy. The opaline, which affects the senses dealing with feeding, causes the predator to instinctively attack the cloud of chemicals as if it were indeed food.

Laboratory use

''A. californica'' has become a valuable

laboratory animal Animal testing, also known as animal experimentation, animal research, and ''in vivo'' testing, is the use of non-human animals in experiments that seek to control the variables that affect the behavior or biological system under study. This ...

, used in studies of the

neurobiology Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...

learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, value (personal and cultural), values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machine learning, machines ...

and

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...

, and is especially associated with the work of

Nobel laureate The Nobel Prizes ( sv, Nobelpriset, no, Nobelprisen) are awarded annually by the Royal Swedish Academy of Sciences, the Swedish Academy, the Karolinska Institutet, and the Norwegian Nobel Committee to individuals and organizations who make out ...

Eric Kandel Eric Richard Kandel (; born Erich Richard Kandel, November 7, 1929) is an Austrian-born American medical doctor who specialized in psychiatry, a neuroscientist and a professor of biochemistry and biophysics at the College of Physicians and Surge ...

. Its ubiquity in

synaptic plasticity In neuroscience, synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity. Since memories are postulated to be represented by vastly interconnected neural circuit ...

studies can be attributed to its simple

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes th ...

, consisting of just 20,000 large, easily identified

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s with cell bodies up to 1 mm in size. Despite its seemingly simple nervous system, though, ''A. californica'' is capable of a variety of nonassociative and associative learning tasks, including

sensitization Sensitization is a non-associative learning process in which repeated administration of a stimulus results in the progressive amplification of a response. Sensitization often is characterized by an enhancement of response to a whole class of stim ...

habituation Habituation is a form of non-associative learning in which an innate (non-reinforced) response to a stimulus decreases after repeated or prolonged presentations of that stimulus. Responses that habituate include those that involve the intact org ...

, and classical and

operant conditioning Operant conditioning, also called instrumental conditioning, is a learning process where behaviors are modified through the association of stimuli with reinforcement or punishment. In it, operants—behaviors that affect one's environment—are c ...

. Study typically involves a reduced preparation of the gill and siphon withdrawal reflex. Sequencing of its whole genome was approved as a priority by

National Human Genome Research Institute The National Human Genome Research Institute (NHGRI) is an institute of the National Institutes of Health, located in Bethesda, Maryland. NHGRI began as the Office of Human Genome Research in The Office of the Director in 1988. This Office transi ...

in March 2005. The draft genome is available on the

UCSC Genome browser The UCSC Genome Browser is an online and downloadable genome browser hosted by the University of California, Santa Cruz (UCSC). It is an interactive website offering access to genome sequence data from a variety of vertebrate and invertebrate spec ...

.aplCal1 at UCSC Genome Browser Gateway
/ref>

References

* Beeman R.D. (1963) ''Notes on the California species of Aplysia (Gastropoda: Opisthobranchia).'' The Veliger 5(4): 145–147. * Bebbington A. (1977) A''plysiid species from Eastern Australia with notes on the Pacific Ocean Aplysiomorpha (Gastropoda, Opisthobranchia).'' Transactions of the Zoological Society of London 34: 87-147 * Turgeon, D.D.; Quinn, J.F.; Bogan, A.E.; Coan, E.V.; Hochberg, F.G.; Lyons, W.G.; Mikkelsen, P.M.; Neves, R.J.; Roper, C.F.E.; Rosenberg, G.; Roth, B.; Scheltema, A.; Thompson, F.G.; Vecchione, M.; Williams, J.D. (1998). ''Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks''. 2nd ed. American Fisheries Society Special Publication, 26. American Fisheries Society: Bethesda, MD (USA). . IX, 526 + cd-rom pp.
NIH/University of Miami National Resource for Aplysia Facility