Book Review: Eastern Pacific Nudibranchs:

A Guide to the Opisthobranchs from Alaska to Central America

Review by Hans Bertsch

Research Associate, California Academy of Sciences

192 Imperial Beach Blvd., # A

Imperial Beach, CA 91932


Behrens, David W., and Alicia Hermosillo. 2005. Eastern Pacific Nudibranchs: A Guide to the Opisthobranchs from Alaska to Central America. Sea Challengers, Monterey, CA. vi + 137 pp. ISBN 0-930118-36-7

            Everyone loves nudibranchs. Or so it seems to those of us who dive, snorkel, tide pool, surf the web, or are concerned about oceans’ biodiversity. Truly beautiful, biologically intriguing, they deserve to be treated beautifully and intelligently. Dave Behrens and Ali Hermosillo totally fulfill this demanding task for excellence in their new book, Eastern Pacific Nudibranchs: A Guide to the Opisthobranchs from Alaska to Central America.

A Sense of History: Context and Comparisons

            This book is actually the 3rd edition in a series: Pacific Coast Nudibranchs: A Guide to the Opisthobranchs of the Northeastern Pacific (Behrens, 1980; Sea Challengers, Los Osos, CA. 112 pp.), and Pacific Coast Nudibranchs: A Guide to the Opisthobranchs, Alaska to Baja California, 2nd edition (Behrens, 1991; Sea Challengers, Monterey, CA. vi + 107 pp.). Each of the editions demonstrates the current state of our knowledge regarding the cold, temperate and tropical waters of the northeast Pacific. Both the 1st and 2nd editions covered the area from Alaska to the tip of the Baja California peninsula; this 2005 volume covers most opisthobranchs occurring from Alaska to Central America. These works also show the research progress in and our increased understanding of the opisthobranch biota in these NE Pacific faunal zones.

            In the 1st edition, 162 species were listed, including 14 unnamed species. The 2nd edition presented 217 species, with 27 unnamed species, and species names were assigned to 13 of the previously 14 unidentified species.

            Behrens & Hermosillo now report 314 opisthobranch species as occurring in the area covered, with 37 of them unnamed. Over 3/4s of these undescribed species (29 out of 37) are reported from the additional southern region covered in this book. Obviously, this demonstrates both the paucity of our knowledge of the southern Pacific Mexican coast opisthobranch fauna, and the recent long-term in-depth studies being conducted by Ali Heremosillo and colleagues. Of the 27 species in Behrens, 1991, 16 appear with correct binomials in the 3rd edition. Footnote

            The prefaces to the three editions end with passionate clarion calls for knowledge, conservation and appreciation of nudibranchs and all life forms with whom we share this Blue Planet. Each preface provides historical contexts to opisthobranch research along the Pacific coasts of Canada, the U.S., and Mexico. Bertsch (1980) divides these study efforts into precise time spans, based on individuals. Terrence Gosliner (1991 and 2005) updates the recent increases of knowledge about opisthobranch biodiversity and biogeography, anatomy, phylogeny, and natural history. It can properly be said that the period 1980–2005 represents the 6th era following my original designations. This explosion in understanding is due in no small measure to Dave Behrens’ incredibly excellent and challenging prior editions of Pacific Coast Nudibranchs.

Into the 21st Century

            Probably no other major taxon of marine organisms in the NE Pacific has been studied as greatly as the opisthobranchs. This is evidenced not just in descriptions of new species, but also in the multitude of field and laboratory studies. This book is the “go-to” source for a summary of, and introduction to, our current knowledge.

            Dave Behrens (now joined by Ali Hermosillo) continues to set new and higher standards for precise, comprehensive, informative and perfectly illustrated field guides to faunal regions. Following a synecdochic tradition of other field guides (e.g., Hawaiian Nudibranchs by Bertsch & Johnson, and Nudibranchs of Southern Africa by Gosliner), this book’s title is Eastern Pacific Nudibranchs, but the taxonomic coverage extends to members of the more-inclusive opisthobranch taxon. Sea slugs, or even babosas del mar (in Spanish), doesn’t quite reflect the audacious evolutionary responses and beauty of these “butterflies of the sea.” Besides, everybody knows nudibranchs—it is a fine word!

            This is, understatedly, a fine book, tersely and brilliantly written. It must be used. More prosaically, it is an essential part of the scholarly repertoire for all interested in and concerned about nudibranchs, molluscs, and marine faunal biodiversity—in short, all known and unknown biota.

            Nudibranchs provide a microcosm of evolution, the guiding law of biology. For example, they have been used in neuro-physiology, biochemistry and pharmacology, adaptive radiation, cladistics, vicariance and dispersal biogeography, introduced non-native species, functional morphology, and protective, warning and mimetic coloration and shapes.

            This book can be divided into 2 major sections: introductory information and species descriptions.

Introductory Information:

            This section summarizes major features of opisthobranch form and function: a) body form and coloration, reduction of the shell; economic or commercial uses such as medical research (nerve functioning and active antibiotic or chemotherapeutic compounds), underwater diving and photography, and sustenance by indigenous peoples; b) feeding and the radula, correlating tooth structure taxonomically and with generalized prey preferences; c) sensory organs and the rhinophores; d) respiration (both the cerata and the gill), and the defensive uses of the cerata which store nematocysts obtained from prey cnidarians, and autotomize; e) opisthobranch reproduction—mutual cross-fertilization by copulating hermaphrodites, spawn, and egg development which can be incomplete (free-swimming planktotrophic or lecithotrophic veliger larvae) or complete (fully-developed juveniles hatch from the eggs); f) collection (with emphases on ecological searching on prey items and habitat conservation by carefully replacing rolled rocks to their original positions), preservation, and identification; g) biogeography and NE Pacific faunal provinces, incorporating my ideas on the provincial level transition (“ecotonal”) zone along the southern Pacific coast of the Baja California peninsula; and, h) nomenclatural rules and systematics.

            The authors present detailed instructions on how to use this book. They give tips for identification based on external characteristics of shape and color, and the use of the radula for more accurate confirmation of the species’ identity. Especially useful, and superbly illustrated with Dave Behrens’ exquisite black and white line drawings, are the pictorial glossary and the pictorial key to the orders and suborders of Opisthobranchia.

Species Descriptions:

            The heart of the book (fully almost 90%) is the 314 species descriptions. Each species is illustrated by at least one foudroyant color photograph. Multiple pictures show significant color variations within that species. Some are portrait-style “tub shots,” but even more overwhelming are the in situ photographs with their egg mass (e.g., Mexichromis porterae, Roboastra tigris, and Anteaeolidiella indica) or on their prey item (e.g., Corambe steinbergae, Onchidoris bilamellata, and Lomanotus vermiformis).

            Each species has a clear, precise, accurate, “cookie-cutter” text. Genus, species, author and year, and a vernacular “common” name are followed by 5 features: identification (body shape and color), radula (rows and teeth formula given when present or if known), natural history (often food preference, but sometimes depth range, activity time, or chemical secretions), size (in mm, the worldwide standard), range, and etymology. The word origins are especially fascinating, including both the obvious (Platydoris macfarlandi) and the obtuse (Glossodoris sedna).

            A bibliography providing an excellent entry into the relevant literature and a family and binomial taxa index conclude this outstanding book.

            Behrens & Hermosillo, 2005, is a full book. There is not a wasted word nor illustration. It is scientifically accurate, and artistically beautiful!

            This book can (and should) be ordered from Sea Challengers Natural History Books: