Description: Body usually 25-75mm, but can reach 260mm. Bright orange to light yellow or sometimes white. Nudibranch has dark markings between but not on the tubercles (picture). Has finger-shaped oral tentacles, and gills numbering six. This species may produce a lot of sweet, fruity-smelling mucus (photo) when disturbed. Its gills and rhinophores are usually lighter in color than is the dorsum (picture). Gills are white-tipped.How to Distinguish from Similar Species: Archidoris montereyensis has dark markings both on and between the tubercles, plus does not produce much mucus or a strong smell. Its gills and rhinophores are usually darker than the dorsum.
Geographical Range: Kodiak Island, Alaska to Isla Coronados (Baja California). Rare in intertidal in southern part of range
Depth Range: Low intertidal zone and subtidal to 35m
Habitat: Common in low intertidal, on rocky shores, harbor pilings
Biology/Natural History: This is the largest of California nudibranchs. It has a penetrating, fruity odor, which may be used to fend off predators. It feeds on a variety of sponges, including Axocielita originalis, Astylinifer arndti, Hymenamphiastra cyanocrypta, Lissodendoryx firma, Halichondria panicea, Haliclona permollis, and species in the genera Mycale, Zygherpa, Parasperella, and Prianos. It may also ingest quantities of organic detritus. Studies show that individual nudibranchs are conservative in their food habits; they tend to keep eating the same food species, even if they are transferred to other sites. Spawning period varies with location, but extend for several months. The mating is reciprocal; partners may be of vastly different size. This species is a simple organism to study the nervous system and thus has been used for much neurophysiological research.
Sponges which live on the motile scallop Chlamys hastata are less vulnerable to predation by this nudibranch.