Dialula sandiegensis (Cooper, 1862)

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

  Discodoris sandiegensis
  Dialvia sandiegensis
Phylum Mollusca
 Class Gastropoda
   Subclass Opisthobranchia
    Order Nudibranchia
      Suborder Doridacea
       Family Discodorididae
Dialula 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.  Its characteristic blackish-brown rings which are up to 1.5 cm diameter make it easy to recognize.  Dorsal surface is firm, spicules in it feel gritty.  Kozloff (1996) key says the rings usually are surrounded by a white ring but I have not often seen that.

How to Distinguish from Similar Species: The large dark rings make this dorid easy to distinguish. However, it is very similar to another species, Discodoris heathi, which has spots instead of rings.  In my observations, spots seem to grade into rings.

Geographical Range: Alaska south to Puerto Penasco, Mexico

Depth Range: Low intertidal and subtidal to 35 m.  Mostly intertidal in the north, subtidal in the 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

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

This species is sometimes cream or even yellow.  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.  Photo by Dave Cowles, July 2005

A pair at Cape Flattery.  Photo by Dave Cowles

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