Opisthobranch of the Week is <i>Diaulula sandiegensis</i>

Diaulula sandiegensis Complex

Image courtesy of Tabitha Lindsay

The use of molecular tools (particularly DNA sequence data) has facilitated the discovery of previously difficult to recognize species. In the Eastern Pacific several new species of nudibranchs have been recognized during the last few years using these techniques. In most cases we thought these new species were just color variations, for example Hermissenda opalescens was considered a synonym of Hermissenda crassicornis and Doriopsilla fulva was considered a synonym of Doriopsilla albopunctata. However these species pairs are genetically distinct. It was only when the molecular data became available that we were able to recognize external traits to distinguish these species. Species that can only be recognized after DNA data is available are called pseudocryptic.

Now we report a new example of pseudocryptic species pairs, the common, widespread, and well-known species Diaulula sandiegensis is a complex of two species. Behrens & Valdes (2001) studied this species in detail across its entire range, using anatomical information and concluded there was only one species. However, a new study using molecular information as well as ecological and reproductive behavioral data concluded that Diaulula sandiegensis is actually two species that overlap in range along the North Eastern Pacific coast. These two species are pseudocryptic and can be distinguished externally.

The first species, Diaulula sandiegensis is found from the outer coast of northern Baja California, Mexico, to Barkley Sound, British Columbia, Canada; however it is rare from northern California to Washington, only to become common again subtidally in Washington and British Columbia. This species is recognizable because it lacks dark spots on the mantle margin.

The second species, Diaulula odonoghuei has a large geographic range across the North Pacific, from Korea, Japan and the Russian Far East to the Pacific coast of North America southwards to Bodega Bay in northern California. This is the dominant species intertidally from Alaska to Fort Bragg, California, and can be recognized because it has dark spots on the mantle margin.

The photographs above illustrate the color variation in both species. A-B, Diaulula odonoghuei; C-D, Diaulula sandiegensis.

And stay tuned, there will be more Eastern Pacific surprises coming up!

References:

BEHRENS,D.W.& VALDES,A.2001.The identityof Doris(s.l.)species Macfarland,1966(Mollusca,Nudibranchia,Discodorididae):a persistent mystery from California solved. Proceedings of the California Academy of Sciences,52:183-193.

Dr.Angel Valdes
Department of Biological Sciences
California State Polytechnic University
3801 West Temple Avenue
Pomona, California 91768-4032
Send Angel email at aavaldes@cpp.edu

From left to right, Terry Gosliner, Angel Valdes, Dave Behrens La Jolla, Calif.

Send Dave email at davidwbehrens@gmail.com