large dorid (up to 8 cm)
nudibranch. Anus is on the midline about 1/4 from the
and is surrounded by 6 gills which are fully retractible.
pale gray (photo)
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
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
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.
intertidal, surge channels
Feeds on Halichondria,
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
neurons involved produce pedal peptides which elicit an increase in the
rate of beating of cilia on the foot, resulting in crawling.
and Carlton, 1975
et al., 1980
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,
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,
Authors and Editors of Page:
Dave Cowles (2005): Created original page