Hermissenda crassicornis

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Hermissenda crassicornis
Opalescent nudibranch hermissenda crassicornis california point joe 2013.jpg
Closeup of Hermissenda crassicornis off Monterey, California
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
(unranked): clade Heterobranchia

clade Euthyneura
clade Nudipleura
clade Nudibranchia
clade Dexiarchia
clade Cladobranchia
clade Aeolidida

Superfamily: Aeolidioidea
Family: Facelinidae
Genus: Hermissenda
Species: H. crassicornis
Binomial name
Hermissenda crassicornis
Eschscholtz, 1831

Hermissenda crassicornis is a species of small, brightly colored, sea slug or nudibranch, a marine gastropod mollusk in the family Facelinidae.[1]

This species is also commonly known as the "opalescent sea slug."


This nudibranch lives from Kodiak Island, Alaska, to Punta Eugenia, Mexico.

The species has also been observed in Bahia de los Angeles, Gulf of California, and in Japan and along the South East Indian Coast.[2]


Five individuals of Hermissenda crassicornis in a Central California tidepool

It can be found in various habitats, including the intertidal zone of rocky shores, but also in bays and estuaries.


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.

Life habits[edit]

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.


  1. ^ 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
  2. ^ "Hermissenda crassicornis". The Slugsite. Retrieved 17 April 2006. [dead link]
  • Sea Slug Forum, species fact sheet:[1]


  • Behrens David W., 1980, ‘’Pacific Coast Nudibranchs: a guide to the opisthobranchs of the northeastern Pacific’’, Sea Challenger Books, California