The "Yellow-Margin Dorid" complex
By Greg Jensen and Karin Fletcher

This week's BOW was a bit of a hassle to put together, but my publisher/coauthor, Greg Jensen, and coauthor, Karin Fletcher, made it happen. This is one of several taxonomic situations that arose while preparing the new revision of Eastern Pacific Nudibranchs. The title of the revision is - Nudibranchs and Sea Slugs of the Eastern Pacific and will be available soon from Mola Marine at

While preparing the description of what had been a single species of white Cadlina with a yellow margin, historically called Cadlina luteomarginata, we realized we had a problem if we expected readers to be able to ID the species because there are now four described "yellow-margin dorid" species that are practically indistinguishable externally. The photo below represents the species complex, but even we can't determine whether the Cadlina in this photo is the true Cadlina luteomarginata or one of the other species.

Photo from Page 87 of Nudibranchs and Sea Slugs of the Eastern Pacific, 2022

The three new look-a-likes were known to be genetically distinct as far back as 2011 (Johnson, R., 2011) but not described or named until 2020 (Korshunova, et. al., 2020).

The photo below shows the group of four in this complex.

Photo from Page 87 of Nudibranchs and Sea Slugs of the Eastern Pacific, 2022

However, too few specimens were examined in the 2020 paper to develop a key for identifying the four species externally so we can only state that there are four described species. Also, since that paper was published there now appears to be a fifth species within this complex as seen in this tree adapted from one generated from BOLD. (The Barcode of Life Data System (BOLD) is an informatics workbench aiding the acquisition, storage, analysis and publication of DNA.)

Our hope is that readers of this BOW or readers of our book take up the challenge and photograph and sequences many more specimens from this complex so that each species may be distinguished externally, if possible, and the true range of these species may be known.


JOHNSON, R. F. 2011. Breaking family ties: taxon sampling and molecular phylogeny of chromodorid nudibranchs (Mollusca, Gastropoda). Zoologica Scripta 40(2): 137-157.

KORSHUNOVA, T., FLETCHER, K., PICTON, B., LUNDIN, K., KASHIO, S., SANAMYAN, N., SANAMYAN, K., PADULA, V., SCHRÖDL, M., MARTYNOV, A. 2020. The Emperor's Cadlina, hidden diversity and gill cavity evolution: new insights for the taxonomy and phylogeny of dorid nudibranchs (Mollusca: Gastropoda). Zoological Journal of the Linnean Society 20: 1-66.

Dave Behrens
Sammamish, WA 98074
July., 2022
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Image courtesy of Greg Jensen

Greg Jensen is an Instructor at the University of Washington's School of Aquatic and Fishery Sciences and teaches Crustacean Biology at the Bamfield Marine Sciences Centre in British Columbia. He is the author of "Crabs and Shrimps of the Pacific Coast" and "Beneath Pacific Tides", and resides in Bremerton, Washington with his wife, dive buddy, and fellow crab biologist Pam and several troublesome turtles.

His books are available through Amazon, or better yet, his website (

Greg's camera equipment: Olympus EM-5 in Olympus housing and Sea & Sea YS-01 strobe; kit lens

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Photo courtesy of Doug Miller

Karin Fletcher and her husband, Doug Miller, have been scuba diving in Puget Sound since 2006. In 2009, they moved to a house on Rich Passage near Bremerton, WA where they dive at least once a week, sometimes while dodging boat traffic. Karin has been tracking nudibranch abundance and diversity in Rich Passage since then and Doug tracks fish and invertebrates for

Karin uses an Olympus TG-5 in an Olympus housing.

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