Sea Hares are marine animals that inhabit coastal regions thick with vegetation. This particular species, Aplysia californica, ranges from Northern California to Baja California.
Biogeographic Regions: pacific ocean (Native )
The California Black Sea Hare is probably the world's largest gastropod. It can weigh up to 35 pounds! It is typically about 16" long (41 cm) and 8" (20 cm) wide and high. Plump and soft, it has winglike flaps around the top of its head on both sides. Aplysia californica can be reddish, brownish, or greenish, spotted with white or dark circles and lines. The colors reflect the type and color of algae they are prone to eat. They feed with a pair of jaws and a grasping radula. On top of their head, two pairs of antennae are found: one low near the mouth and another behind the eyes. A foot used to help in locomotion extends a little farther than the entire length of the animal. The anterior tentacles are much larger and ear-like (thus its common name- the sea hare) than the second pair which are used more for smelling. They also possess winglike flaps called parapodia that are used for swimming. The mantle folds over and covers a thin, transparent, and flexible shell. In its wall are unicellular glands that secrete a purple dye when the animal is handled. The sea hare does possess a developed nervous and digestive system. In its digestive tract there is an alimentary canal in front of the stomach that ends in a crop lined with horny plates for better mastication before digestion of food.
Other Physical Features: ectothermic ; bilateral symmetry
Aplysia californica are marine animals that inhabit coastal regions thick with vegetation. This particular species ranges from Northern California to Baja California. They can usually be found crawling around the seaweed they use as a source of food. The younger generation live in the deeper waters where they are born while the adult generation lives in shallow, sheltered places with low tide.
Inactive when exposed to air to conserve oxygen. Can often lead to desiccation and anoxia.
Aplysia californica are herbivorous and feed on a variety of algae and eelgrass. Their pair of jaws and broad rasp-like radula help crop the seaweed they eat. The color of the particular animal matches the color of the algae or vegetation they feed on the most.
Defense mechanism against California spiny lobster
When attacked by spiny lobsters(P. interruptus), A. califonica release a mixture of ink and opaline as a chemical defense to escape. The amino acids in the ink-opaline stimulate chemoreceptor neurons, resulting in inappropriate behaviors. It also deceives spiny lobsters into focusing on false food or cleaning behaviors. The ink-opaline can inhibit ingestion if eaten by spiny lobsters or force them to groom their antennae or mouthparts.
Life History and Behavior
Life Cycle Phases: Embryonic (10 days), Larval/Planktonic (34 days), Metamorphic (2-3 days), Juvenile (90 days), Adult.
A. californica is hermaphroditic. Armed with a single aperture and duct for the sperm and ova, this species reproduces sexually. They travel to deeper waters to spawn around spring time. Once fertilized, their eggs are laid down in pink, gelatin-like stringed sacs coiled around seaweed or rocks.
Evolution and Systematics
The California sea hare inhibits microbial growth using escapin, a polypeptide.
"Escapin's antimicrobial effects, bacteriostasis and bactericidal, were determined using a combination of two assays: (1) incubation of bacteria on solid media followed by assessment of inhibition by direct observation of zones of inhibition or by turbidity measurements; and (2) incubation of bacteria in liquid media followed by counting viable colonies after growing on agar plates. Native escapin inhibited the growth of Gram-positive and Gram-negative bacteria, including marine bacteria (Vibrio harveyii and Staphylococcus aureus) and pathogenic bacteria (Staphylococcus aureus, Streptococcus pyogenes and Pseudomonas aeruginosa). Escapin also inhibited the growth of yeast and fungi, with different efficacies. Escapin's antimicrobial activity was concentration dependent and did not decrease when stored for more than 5 months at room temperature. Escapin was bacteriostatic and not bactericidal in minimal media (e.g. salt media) with glucose, yeast extract, and a mixture of 20 amino acids each at 50 µmol l-1, but was bactericidal in media enriched with Tryptone Peptone. Escapin was also strongly bactericidal in media with L-lysine at concentrations as low as 3 mmol l-1 and slightly bactericidal in 50 mmol l-1 L-arginine, but not in most other amino acids even at 50 mmol l-1. Escapin had high oxidase activity (producing hydrogen peroxide) with either L-arginine or L-lysine as a substrate and little to no oxidase activity with other L-amino acids. Hydrogen peroxide alone (without escapin or amino acids) was strongly bacteriostatic but poorly bactericidal, similar in this respect to L-arginine but different from L-lysine in the presence of escapin. Together these results suggest that there are multiple mechanisms to escapin's antimicrobial effects, with bacteriostasis resulting largely or entirely from the effects of hydrogen peroxide produced by escapin's LAAO activity, but bactericidal effects resulting from lysine-dependent mechanisms not directly involving hydrogen peroxide." (Yang et al. 2005:3609)
Learn more about this functional adaptation.
Molecular Biology and Genetics
Barcode data: Aplysia californica
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Aplysia californica
Public Records: 2
Specimens with Barcodes: 2
Species With Barcodes: 1
US Federal List: no special status
CITES: no special status
Relevance to Humans and Ecosystems
Aplysia californica are used extensively in studies of behavior, reproduction, and development in such fields as chemistry, biology, and psychology.
California sea hare
The California sea hare, also known as the California sea slug, scientific name Aplysia californica, is a species of sea slug, specifically a sea hare, a marine opisthobranch gastropod mollusk in the sea hare family, Aplysiidae.
This species is found on the Pacific coast of California, United States, and northwestern Mexico (including the Gulf of California). Aplysia inhabit the photic zone to graze on algae, mainly the intertidial and sub-littoral zones usually not deeper than 18-20 m.
The maximum length recorded for the California sea hare is 75 cm (30 in) when crawling and thus fully extended, although most adult specimens are half this size or smaller. Adult animals can weight up to 7 kg (15 lb). A closely related species, Aplysia vaccaria, the black sea hare, can grow to be larger still.
Because of the toxins in its body that come from consuming algae, the California sea hare has very few predators. Among these, however, is the giant green anemone, which reportedly takes them in large numbers; however, the anemone will capture a sea hare and then proceed to digest only 67-85% of it before regurgitating the remains. This is because the anemone consumes only enough of the sea hare to expose the sea hare's digestive gland and its associated toxins. Once this gland has been exposed, it causes the anemone to reject all of the remaining undigested animal, including parts it would otherwise have taken in as food. Other predators include starfish, lobsters, and the ophistobranch Navanax inermis 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.
Like all sea hares, the California sea hare is hermaphroditic, acting as male and female simultaneously during mating. Aplysia is known to form mating chains with up to 20 animals, thus each animal can serve as male and female at the same time. The eggs are yellow-green, and change after 8 to 9 days into a brown color before larvae hatch. Mating is most prominent during the summer month following the rise of the water temperature to 17 degrees Celsius. Aplysia has a generation time of 19 weeks: Day 1-37 after hatching from the egg planktonic stage, day 34-37 Metamorphic stage, day 45-80 juvenile stage (35 days in total). Reproductive maturity is reached 85 days after hatching (133 days after deposition of the fertilized eggs). The development of the nervous system lasts for a total of 140 days  The life span is assumed to be around a year, yet older animals have been found. Cooler temperature delays spawning and has been shown to extend the lifespan.
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.
Like all Aplysia species, the California sea hare is herbivorous. Its diet consists primarily of red algae like Laurencia pacifica, Plocamium pacificum, and Ceramium eatonianum, which gives the animal its typically reddish or pinkish coloration. Thus Aplysia resembles the food it grazes on and cannot be distinguished easily from the seaweed unless the animal is moving.
Its ubiquity in synaptic plasticity studies can be attributed to its simple nervous system, consisting of just 20,000 large, easily identified neurons with cell bodies up to 1 mm in size. 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.
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- NIH/University of Miami National Resource for Aplysia Facility
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