California Opisthobranchs

Having learned to dive in the Marshall Islands, where the annual water temperature varies from 26 to 29 degrees C (79 to 85 F), I found it difficult to make the transition even to Hawaii, although I did dive there frequently for a number of years. Starting to dive in California was an even more difficult step. I made several dives when visiting friends there in 1979 and in the early 80s, then moved to the central coast for a couple of years starting in 1986. I have to admit the colder water and far more involved logistics of diving made this period my dryest two years since starting diving in 1967, but I still managed to make a number of trips out to the Channel Islands off Santa Barbara. My thin tropical blood protested time and time again, but what kept drawing me back out to struggle into the quarter-inch wetsuit and hood were the large and colorful nudibranchs that could be found on every dive. In 2017 we relocated to California and are back to diving at the Channel Islands off Ventura and Santa Barbara, so these pages are once again being updated.

The following is by no means a complete listing of the species of opisthobranch mollusks from the waters of California. These are simply some of the animals we happened to see on our limited number of dives primarily around the islands of Anacapa, Santa Cruz, Santa Rosa, and San Miguel. There are other web sites that cover all these species in much greater depth. In particular, Mike Miller's Slug Site and the Australian Museum's Sea Slug Forum by Bill Rudman have all of these species and many more. The pages below all have links to Slug Site or Sea Slug Forum pages on these animals, and I recommend you go there for more information. There is also printed literature available on these wonderful creatures; the premiere reference on California nudibranchs was David Behrens' Pacific Coast Nudibranchs, now expanded to Eastern Pacific Nudibranchs by David Behrens and Alicia Hermosillo.

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Felimare californiensis

Felimare porterae

'Felimida' macfarlandi


Cadlina flaveomaculata

Cadlina limbaughorum

Cadlina luteomarginata

Cadlina modesta


Conualevia alba


Diaulula sandiegensis

Jorunna pardus

Peltodoris mullineri

Peltodoris nobilis

Thordisa bimaculata


Doriopsilla albopunctata


Ancula gibbosa


Limacia mcdonaldi

Polycera atra

Triopha catalinae

Triopha maculata


Aegires albopunctatus


Armina californica


Tritonia festiva


Dendronotus frondosus


Flabellina iodinea

Flabellina trilineata


Cuthona divae


Austraeolis stearnsi

Hermissenda opalescens

Phidiana hiltoni


Bulla gouldiana


Aglaja ocelligera

Navanax inermis

Navanax polyalphos


Aplysia californica

Aplysia vaccaria


Berthella californica

Berthellina ilisima

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