Aplysia californica

Geographic Range

Sea Hares are marine animals that inhabit coastal regions thick with vegetation. This particular species, Aplysia californica, ranges from Northern California to Baja California. (Grzimek, 1968; Meinkoth, 1981)


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. (Borradaile and Potts, 1963; Grzimek, 1968; Meinkoth, 1981)

Physical Description

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. (Borradaile and Potts, 1963; Meinkoth, 1981; Nichols, 1979)


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. (Borradaile and Potts, 1963; Nichols, 1979)


Aplysia californica lives a predominantly quiet life crawling among the bottom of shallow waters and eating seaweed. Two of its behaviors include head waving and ink secretion.

The patterns of head waving are a complex and important behavioral characteristic that can be used for categorizing the sea hares. The patterns can be quite complex and are not constrained by other body parts (joints, muscles, etc.) and thus exhibit much freedom of movement. In the Aplysia californica there are instances of periodicity of movements, but usually the bouts of head waving are made up of more simple movements. Also, Aplysia californica have an important defensive mechanism in the form of an ink gland that processes and secretes a defensive ink pigment. It obtains the pigment from a diet consisting mostly of red seaweed. When irritated, the ink is released from vesicles stored in membrane-bound vacuoles. (Kuenzi and Carew, 1994; Prince, et al., May 1998)

Food Habits

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. (Buchsbaum, et al., 1989; Meinkoth, 1981; Nichols, 1979)

Economic Importance for Humans: Positive

Aplysia californica are used extensively in studies of behavior, reproduction, and development in such fields as chemistry, biology, and psychology. (Buchsbaum, et al., 1989)

Conservation Status


Sara Sabzevari (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.


Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

native range

the area in which the animal is naturally found, the region in which it is endemic.


2009. "National Resource for Aplysia" (On-line). Rosenstiel School of Marine and Atmospheric Science. Accessed June 22, 2009 at http://aplysia.miami.edu/.

Borradaile, L., F. Potts. 1963. The Invertebrata: A Manual for the use of Students. Cambridge: Cambridge University Press.

Buchsbaum, M., R. Buchsbaum, V. Pearse, J. Pearse. 1989. Living Invertebrates. Pacific Grove, California: The Boxwood Press.

Grzimek, B. 1968. Grzimek's Animal Life Encyclopedia (vol. 3-Mollusks and Echinoderms). New York: Van Nostrand Reinhold Company.

Kuenzi, F., T. Carew. 1994. Head waving in Aplysia californica: 1. Behavioral characterization of searching movements. Journal of Experimental Biology, volume 195, no.0: 35-51.

Meinkoth, N. 1981. The Audubon Society Field Guide to North American Seashore Creatures. New York: Alfred A. Kuopf, Inc..

Nichols, D. 1979. The Oxford Book of Invertebrates. New York, New York: Oxford University Press.

Prince, J., T. Nolen, L. Coelho. May 1998. Defensive ink pigment proessing and secretion in Aplysia californica: concentration and storage of phycoerythrobilin in the ink gland. The Journal of Experimental Biology, Vol. 201, no.10: 1595-1613.