Dendronotus iris (Cooper, 1863)

Common name(s): Giant dendronotus

Synonyms: Dendronotus giganteus
Phylum Mollusca
 Class Gastropoda
  Subclass Opisthobranchia
   Order Nudibranchia
    Suborder Dendronotacea
     Family Dendronotidae
Dendronotus iris captured at 15 m depth, Coffin Rocks
(Photo by: Dave Cowles, August 2005)
Description:  As a Dendronotacean, this species has its anus on the right side (on an anal papilla (photo), dorsal cerata besides the rhinophores, and the clavus of the rhinophores is fully retractable into a sheath.  D. iris has two longitudinal dorsal rows of very bushy cerata which have brick-red, yellow, purple, orange, or white tips.  The gut projects into only the most anterior pair of cerata.  The rhinophores are very large and somewhat similar in shape to the cerata, and the clavus extends from an anterior shelf on them--not obvious at first (photo).  The sheath of the clavus is drawn out into several branched papillae that make it look crownlike.  The large rhinophore stalk has 3-6 bushy projections along its posterior border (photo).  The species has a small oral veil with 4 pairs of oral papillae.  It has a white line around the edge of the foot, but has few or no white dorsal spots (though the gonopore in this individual is ringed in white [photo]).  Can get up to 30 cm long, averages 6-10 cm, and is one of the largest nudibranchs in America.  Color is variable, often a shade of salmon-red or light purple but may be gray or pale as in this individual.

How to Distinguish from Similar Species: D. albopunctatus has a large, wide oral veil and yellowish white spots.  Other Dendronotus, such as D. diversicolor, have no row of bushy projections along the posterior border of the rhinophore stalk.

Geographical Range:  Unalaska Island, Aleutian Islands to Los Coronados Island, Baja California.

Depth Range:  Mostly subtidal, down to 200 m.  Sometimes seen on the surface over deep water, or in eelgrass flats.

Habitat:  Mostly benthic on soft bottoms.

Biology/Natural History:  This species feeds on the tubedwelling anemone Pachycerianthus fimbriatus, and on Nemertean worms.    Besides its radula, it has large jaws for clipping tentacles off the anemone, and leaves the anemone looking as if it has had a bad haircut.  The nudibranchs are sometimes pulled into the tube when the anemone retracts, but do not seem to be harmed by this.  Predators include Pycnopodia helianthoides.  This nudibranch is very active (see movie) and can readily swim by gyrating the body.  Eggs are laid in white strings (photo), often on the tubes of their prey.  The heart of this individual was large, and the heartbeat was easily seen through the dorsal surface (see movie).

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:
  Flora and Fairbanks, 1966 (as D. giganteus)
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:
Behrens, 1991
Harbo, 1999
Johnson and Snook, 1955 (as D. giganteus)
Wrobel and Mills, 1998

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

Web sites:

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

The white-ringed gonopore on the right side, and the anal papilla (light colored, to the right of the gonopore and benind and below the right rhinophore) can be seen in this photo.
Photo by Dave Cowles, August 2005

The rhinophores (left one shown here) have a series of projections on the posterior side.  The clavus is perfoliate, retractable, and projects from an anterior shelf.  It has a crownlike ring of projections around it.
Photo by Dave Cowles, August 2005

The eggs are laid in gelatinous white strands, which are often attached to the tubes of their anemone prey.

This nudibranch is very active, rapidly swirling its cerata around when it crawls or swims.  Click here for a movie of the animal waving its cerata.

The heart of this nudibranch is large and easily seen beating through the dorsal surface.  Click here for a movie of the heartbeat.

At Urchin Rocks

This individual was seen in a high intertidal tide pool at Urchin Rocks, July 2020 (Dave Cowles). Several people reported seeing stranded individuals of this species in the Salish Sea at about that period. Strandings may occur after reproductive aggregations.

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