Nudibranchs

Photo 1:  Triopha catalinae or the Clown Nudibranch.  

 

Seen dock pilings at Friday Harbor, San Juan Island, WA. 

 

Photo by  Michael D. Miller

Life History

 

Nudibranchs, or Sea Slugs, are commonly found in Washington’s marine waters, however these molluscs are also found globally at depths ranging from the intertidal to depths of several hundred meters. 

Nudibranchs have evolved towards a reduction or even a complete loss of an external or internal shell.

While some nudibranchs species exhibit dramatic aposematic coloration other species are highly cryptic.

 

Basic Nudibranch Taxonomy

 

Kingdom:  Animalia

Phylum:  Mollusca

Class:  Gastropodia

             Subclass:  Opistohobranchia

Order Nudibranchia. 

             Suborders:      Doridacea

                                       Dendronotacea

                                       Arminacea

                                       Aeolidacea

 

(Behrens 1991, Kozloff 1993, Levinton 2001)

Species Identification

Rhinosphores and Cerata

 

Photo 2:  Aeolidia papillosa observed in various locations in the San Juan Islands and Fox Island, Washington. 

 

Photo by Steve Gardner, La Jolla, California

Rhinosphores and Gill Rosettes

 

Photo 3:  Diaulula sandiegensis observed at Point Defiance, Tacoma, Washington. 

 

Photo by Michael D. Miller, The Slug Site.

Michael D. Miller

Rhinosphore structures

 

Photo 4:  Tritonia festiva observed in Friday Harbor, San Juan Washington. 

 

Photo by Lisa Hannon

Lisa Hannon, 2007

Cerata Structures

 

Photo 5:   Aeolidiella foulisi  .

 

Photo by Bill Rudman of the Australia Museum. 

Bill Rudman

Anatomy

 

Rhinosphores

 

Wide variability among species — some smooth while others are very elaborate

 

Distal end of rhinosphore shaped like gills or tentacles but really a sensory organ

 

 

Gills

 

Wide species variability—can be found dorsally in cerata structures or gill rosettes. 

 

Some species have gills under the mantle edge.

 

Cerata

 

Act as a defense mechanism

 

Can be a gill structure

 

Also acts as a digestive structure

 

Defenses

 

Aposematic or Cryptic Coloration

 

Mimicry

 

Toxic secretions

 

Stinging nematocysts in cerata — obtained from food sources such as hydroids or anemones

 

 

(Behrens 1991, Miller 2007, Rudmand 2007)

Four Common Washington State Nudibranch Suborders

(Behrens 1991)

Doridacea

· Most common Nudibranch

 

· Gills form a circlet or rosette structure dorsally around the anus or gills can also be found under the mantle

Dendronotacea

· Row of Cerata along edges of notum

 

· Unique rhinosphores—cup like sheath

Arminacea

· Smallest suborder

 

· Gills appear as cerata

Aeolidacea

· Clusters or groups of cerata

 

· Cerata store defensive nematocysts in tips