Key to Order Nudibranchia

[Nudibranchs have exposed, unprotected gills.  Adults have no shell (the larval shell is lost).]

Taken primarily from  Kozloff, 1987, 1996  (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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1a	Anus, partly or completely encircled by gills, located on the midline of the dorsum, one-half to three-fourths of the body length from the anterior end	Suborder- Doridina (In part)
1b	Anus not located on the midline of the dorsum ( it is either on the right side, on the dorsum near the right side, or at the posterior end of the body; if gills are present, they are not arranged in a partial or complete circle around the anus)	2
2a	Anus at the posterior end of the body, on the midline, in a deep groove in the mantle between the foot and the edge of the dorsum; dorsum without any outgrowths other than the rhinophores	Suborder- Doridina (In part)
2b	Anus on the right side of the body, or on the dorsum near the right side; dorsum usually with outgrowths (simple or branched cerata, or gills) in addition to rhinophores ( if dorsal outgrowths are not present, the dorsum has several white longitudinal ridges on a pinkish brown background)	3
3a	Without dorsal outgrowths other than the rhinophores; dorsum with several white longitudinal ridges on a pinkish brown background (Suborder Arminacea in original key)	Suborder Cladobranchia,  Superfamily Arminacea: Armina californica
3b	With dorsal outgrowths (cerata or gills) in addition to the rhinophores; dorsum without white longitudinal ridges	4
4a	Clavus of the rhinophores partly or fully retractile into the sheath; dorsal outgrowths either club-shaped cerata (with rings of prominent tubercles), paddlelike or bushy cerata, or bushy gills (as a rule, there are 4 to 10 cerata or numerous gills arranged in each of 2 dorsolateral longitudinal series) (Suborder Dendronotacea in original key)	Suborder Cladobranchia,  Superfamily Dendronotacea
4b	Clavus of rhinophores not retractile into a sheath (each rhinophore stands free; it has no sheath); dorsal cerata cylindrical, lanceolate, or leaflike, usually numerous (more than 20) and usually arranged in transverse rows	5
5a	Anus on a conspicuous papilla near the right side of the posterior third of the dorsum, usually among the posterior third of the cerata (Suborder Arminacea in original key)	Suborder Cladobranchia, Superfamily Arminacea (in part)
5b	Anus on an inconspicuous papilla near the right side of the anterior half of the dorsum, usually among the anterior third of the cerata (Suborder Aeolidacea in original key)	Suborder Cladobranchia, Superfamily Aeolidacea

  Suborder Aeolidacea
  Armina californica
  Suborder Arminacea
  Suborder Dendronotacea
  Suborder Doridina