Biology/Natural History: It is one of the most abundant nudibranchs in Califonia. It eats hydroids, but the diet also includes small sea anemones, bryozoans, colonial ascidians (Aplidium solidum, botryllids), annelids, small crustacea, tiny clams, dead animals of any sort. Will eat other Hermissenda. In the Puget Sound, Hermissenda is the main predator of the sea pen Ptilosarcus gurneyi. Mating animals are most often found in southern California in winter, but are found year around in the Puget Sound (Washington). The egg string resembles linked pink sausages. They are commonly attached to algae and to blades of eelgrass. Each egg case usually contains one egg, but can contain up to four. Many studies have been carried out on Hermissenda, but the main area of focus is the eye. It has five cells, each about 75 um in diameter, which are large enough to receive a recording electrode. Within the cells it is suspected of containing symbiotic fungi. Hermissenda is an aggressive creature. When two individuals encounter fights will break out, which involves lunging and biting. Encounters most likely to induce a fight are those of mutual head on contact. The individual whose head is closest to the others tail or side will usually get the first bite in, this also means that they usually come out the winner. The copepod Hemicyclops thysanotus is often found adhering to the dorsal surface of Hermissenda.
The nudibranch Phidiana hiltoni may attack this nudibranch (Goddard et al., 2011)
- Behrens, David W., 1991. ; PacificCoast Nudibranchs, 2nd ed. ; Sea Challengers, Monterey, CA. ; ISBN0-930118-17-0. ; Paperback, 107 pp. ; This excellent paperbackhas color photos and brief descriptions of the nudibranchs, anaspideans,notaspideans,, sacoglossans, and cephalaspideans found along the Pacificcoast, some of which possess a shell. ; Includes a glossary with diagrams,and a pictorial key to opisthobranch suborders. http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Annotated_Bibliography.html#Behrens+1991
- McDonald,Gary R. and James W. Nybakken, 1980. ; Guide to the Nudibranchsof California. ; American Malacologists, Inc. ; Paperback (largepage size), 72 pp. ; ISBN 0-915826-08-9. ; Contains photos anddescriptions of many nudibranchs, primarily from California but also includingmost species from Alaska to Oregon. ; Also includes a key and glossary. http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Annotated_Bibliography.html#McDonald+and+Nybakken+1980
Hermissenda crassicornis are commonly found in areas of the West Coast of North America from Kodiak Island, Alaska to Baja California, Mexico. They are benthic organisms that can be found crawling on rocks, seaweed, and various other substrates on the ocean floor.
Biogeographic Regions: nearctic (Native )
The Hermissenda crassicornis is one of the most beautiful of all the invertebrates. Its length is 3 and 1/4 inches long, on average, and its width, 3/8 inches. The distinctive colors of the H. crassicornis are bluish-white with an orange line down the middle of its back. The margins have pale electric blue lines. These colors are mainly carotenoids and carotenoproteins. There are two pair of tentacles (rhinophores) located on the top of the head. The first pair has blue lines, and the second pair is bluish with raised rings. In the middle, there are numerous finger-like projections, called cerata, in two clusters on each side of the back. These projections are brilliantly colored in bright orange with a white tip on each ceratum. The coloration of the H. crassicornis serves as a great identification factor for the species.
Unlike most other Mollusks, the H. crassicornis lack a shell, mantle cavity, and original gill.
Other Physical Features: ectothermic ; bilateral symmetry
H. crassicornis can be found around tidepools, and on rocks, pier pilings, and mudflats. It can also be found from low-tide line water to water 110 feet deep.
(Pearse,et al 1989)
Depth range (m): 1 - 1.3
Depth range (m): 1 - 1.3
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Habitat: Common in spring and summer, varied habitats, usually found in rocky pools, marina floats, pilings, and mud flats.
Hermissenda crassicornis feed on a wide variety of animals, such as hydroids, sponges, corals, and many other types of invertebrates. In some instances, they can become cannibalistic, eating other nudibranchs. The H. crassicornis will fight each other, struggling to bite chunks of tissue from each other.
Studies have been done that indicated that H. crassicornis locates its food by chemotaxis. This study also looked at the most profitable food items for H. crassicornis The feeding experiments demonstrated that a diet of Turbularia resulted in a higher growth rate in the H. crassicornis than any of the other organisms used in the experiments, such as Ciona viscera or mussels. These last two organisms are most likely used for maintenance diets.
(Tyndale, et al 1994)
Life History and Behavior
Hermissenda crassicornis is a hermaphrodite, possessing both male and female organs. Self-fertilization is a very rare occurance among the H. crassicornis. Most mate, and then lay their eggs near their food source. The H. crassicornis can lay a wide range of eggs on a strand, containing from a few to a million. The maturation of the egg is highly influenced by temperature and can take as little as 5 days or as long as 50 days. The development of the egg is most favorable in warm temperatures. The egg develops into a larval stage called a veliger that floats around on the ocean floor until environmental conditions cause the veliger to settle and develop into adult form.
Recent experiments have determined that the H. crassicornis produce long-term planktotrophic velliger larva. They are unable to metamorphosize for at least three weeks. The best time for inducing metamorphosis is at approximately day 41 to 50 in an egg mass. This varies, however, within the different egg masses. Studies show that this is most likely due to the gradual aquisition of metamorphic competence.
(Avila 1998, Nordin 1996)
Relevance to Humans and Ecosystems
Hermissenda crassicornis is a great subject for study on the cellular level. H. crassicornis has been used as a biomedical research model for many physiological properties, such as learning and memory studies. It has also been used as a model for lead toxicity studies. In these studies, lead significantly reduced the ability for H. crassicornis to undergo associative conditioning and effected the ability for H. crassicornis to aquire associative learning. The behavioral studies can be related to identifiable cells in the ganglia of the head.
(Tyndale, et al 1994, Kuzirian, et al 1996)
This species is also commonly known as the "opalescent sea slug."
The species grows to be about 50 mm, or about 2 inches. The color of this nudibranch varies from one locality to another, but it is always easily recognizable by the orange stripe along its back.
It is often confused with the Caloria Indica, though differs from it by the having a larger number of branches, creating a dense, fur-like pattern.
This slug has been also used in several studies about Beta thymosins.
This nudibranch feeds on hydroids and other marine organisms such as ascidians and sea anemones. It sometimes attacks other nudibranchs, and will eat smaller specimens of its own species. It is host to the ectoparasites Halicyclops thysanotus Wilson C.B., 1935 and Hemicyclops thysanotus Wilson C.B., 1935.
- Rosenberg, G. (2011). Hermissenda crassicornis (Eschscholtz, 1831). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=367883 on 2012-06-03
- "Hermissenda crassicornis". The Slugsite. Retrieved 17 April 2006.[dead link]
- Sea Slug Forum, species fact sheet:
- Behrens David W., 1980, ‘’Pacific Coast Nudibranchs: a guide to the opisthobranchs of the northeastern Pacific’’, Sea Challenger Books, California
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