Diaulula sandiegensis (Cooper, 1862)

Common name(s): Ring-spotted dorid, San Diego dorid

  Doris sandiegensis, Discodoris sandiegensis
  Dialvia sandiegensis
Phylum Mollusca
 Class Gastropoda
   Subclass Opisthobranchia
    Order Nudibranchia
      Suborder Doridacea
       Family Discodorididae
Diaulula sandiegensis, Balboa Island, Ca
(Photo by: Dave Cowles, May 1999)
Description:  A large dorid (up to 8 cm) nudibranch.  Anus is on the midline about 1/4 from the posterior end and is surrounded by 6 gills which are fully retractible.  Usually pale gray (photo) but may be yellow or white or even orange or dark brown.  Its characteristic blackish-brown rings which are up to 1.5 cm diameter and often surrounded by a white ring make it easy to recognize.  On this species the rings (occasionally spots) are found only on the central part of the dorsum and not near the mantle margins. The rings usually number around 4 to 41 (mean 10). They increase in size but not in number with age. However, recently a separate species, considered by Kozloff to be a variant of this species, has been recognized (Lindsay et al., 2016). Dorsal surface of D. sandiegensis is firm, and the spicules in it feel gritty. See below for how to distinguish the two species.

How to Distinguish from Similar Species: The large dark rings make this dorid easy to distinguish. However, what formerly was considered a variant of this species is now recognized by molecular and morphological criteria as a separate species, Diaulula odonoghuei. D. odonoghuei has mainly spots (occasionally rings) on both the central part and the edges of its dorsum. The spots in D. odonoghuei both grow and increase in nunber with age, and range in count from around 23 to 234 (mean = 76). It is also similar to another species, Discodoris heathi, which also has spots instead of rings.  

Geographical Range: Vancouver Island south to Puerto Penasco, Mexico

Depth Range: Low intertidal and subtidal to 35 m.  Lindsay et al. (2016) state that this species is almost exclusively subtidal in the Pacific Northwest but is often intertidal from northern California south.

Habitat: Rocky intertidal, surge channels

Biology/Natural History: Feeds on Halichondria, Haliclona, Myxilla, and Petrosia sponges.  The egg ribbon is narrow, white, attached in an oval spiral under rock ledges by one margin.

According to Baltzley et al., (2011), many gastropods, including this species, have a special network of pedal ganglia in their foot which assists in crawling.  The two main neurons involved produce pedal peptides which elicit an increase in the rate of beating of cilia on the foot, resulting in crawling.

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Dichotomous Keys:
Kozloff 1987, 1996
Smith and Carlton, 1975

General References:
Kozloff, 1993
Niesen, 1994
Morris et al., 1980

Scientific Articles:
 Baltzley, Michael J., Allison Serman, Shaun D. Cain, and Kenneth J. Lohmann, 2011.  Conservation of a Tritonia pedal peptides network in gastropods.  Invertebrate Biology 130: 4 pp. 313-324

Lindsay, Tabitha, Julie Kelly, Anton Chichvarkhin, Sean Craig, Hiroshi Kajihara, Joshua Mackie, and Angel Valdes, 2016. Changing spots: pseudocryptic speciation in the North Pacific dorid nudibranch Diaulula sandiegensis (Cooper, 1863) (Gastropoda: Heterobranchia). Journal of Molluscan Studies 82:4 pp 564-574. doi:10.1093/mollus/eyw026

General Notes and Observations:  Locations, abundances, unusual behaviors:

This species is sometimes cream or even yellow.  Notice how the rings are found on the central part of the dorsum but not on the margin.
Photo by Dave Cowles, Balboa Island, May 1999

This individual, from 10 m depth near Northwest Island, WA, is the color pattern I more typically see.  The lack of rings near the margin fit the definition of D. sandiegensis, which is nearly exclusively subtidal at these latitudes according to Lindsey et al., (2016). However, it was found well inland from the open coast, in a more protected area which Lindsey et al., (2016) suggested was the domain of D. odonoghuei. Photo by Dave Cowles, July 2005

Authors and Editors of Page:
Dave Cowles (2005):  Created original page