Hermissenda crassicornis
(Eschscholtz, 1831)

Order: NUDIBRANCHIA
Suborder: AEOLIDINA
Family: Glaucidae

DISTRIBUTION

West Coast of North America from Kodiak Island, Alaska to Baja California, Mexico. NW Pacific - Japan and Sth Korea (Behrens & Hermosillo, 2005; Sea Slug Forum records).

PHOTO

UPPER: Monterey Bay Aquarium, California.
LOWER: Egg ribbon, Los Angeles, California.
PHOTOS: Daniel L. Geiger.

The body is translucent clear with a very characteristic pattern of white or bluish-white lines, yellow-orange patches and bluish white dusting. The upper half of both the oral tentacles and the rhinophores are dusted with white. A opaque white line runs from the tip of each oral tentacle down the posterior edge of the dorsal surface of the tentacle to the head. Here it splits in two, one branch running up to join its partner from the other oral tentacle to run down the dorsal midline to the posterior tip of the body. The other branch runs along the edge of the mantle, with breaks between the ceratal clusters. The white lines running between the rhinophores join just behind the rhinophores, then separate again in the interhepatic space behind the first ceratal cluster. They join again about halfway down the body to run as a single line to the posterior tip of the body. There is a bright orange median line [sometimes white yellow or red] which runs from between the rhinophores, forward about halfway across the head. A shorter line of the same colour lies in the interhepatic space between the two white lines. There is also a white line running along the edge of the foot. There is some colour variability in this species, the white lines in particular, can appear quite blue, and sometimes they are a broad faint band, other times there can be a thin intense white line with a broad band of white dusting running alongside. The ceratal colour can also vary. Usually the digestive gland is a shade of brown and the cerata are tipped with white and may have a subapical band of orange. One variety has a white line up each ceras. In others, the ceratal color is faded, forming bands of white and brown. The rhinophores range from almost smooth to slightly wrinkled. In some cases quite distinct rings can be present. It grows to about 50 mm.

References:
• Avila, C. (1999) Chemotaxis in the nudibranch Hermissenda crassicornis: does ingestive conditioning influence it behaviour in a Y-maze? Journal of Molluscan Studies, 64: 215-222
• Avila, C., Tyndale, E., & Kuzirian, A.M. (1998) Feeding behaviour and growth of Hermissenda crassicornis (Mollusca: Nudibranchia) in the Laboratory. Mar. Fresh. Behav. Physiol., 31: 1-19.
• Behrens, D.W. (1980) Pacific Coast Nudibranchs. A guide to the opisthobranchs of the northeastern Pacific. Sea Challengers. Los Osos, California.
• Harrigan, J.F. & Alkon, D.L. (1978). Larval rearing, metamorphosis, growth and reproduction of the aeolid nudibranch Hermissenda crassicornis (Eschscholtz, 1831). Biological Bulletin, 154: 430-439.
•Longley, R.D. & Longley, A.J. (1981) Hermissenda: agonistic behaviour or mating behaviour? The Veliger 24(3):, 230-231.
•Rutowski, R.L. (1983): Mating and egg mass production in the aeolid nudibranch Hermissenda crassicornis (Gastropoda: Opisthobranchia). Biological Bulletin, 165(August): 276-285.

Authorship details
Rudman, W.B., 2003 (August 2) Hermissenda crassicornis (Eschscholtz, 1831). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/hermcras

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