Taken primarily from Kozloff, 1987, 1996 p. 254 (Copyright 1987, 1996, University of Washington Press. Used in this web page by permission of University of Washington Press)
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| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 1a | Without cerata: dorsum with several white longitudinal ridges on a pinkish brown background (these ridges converge anteriorly toward the rhinophores) (on sandy substrata) | Armina californica |
| 1b | With cerata; dorsum without white longitudinal ridges | 2 |
| 2a | Cerata slender, circular or only slightly oval in cross-section, and approximately the same diameter over most of their length; without a prominent oral veil. | 3 |
| 2b | Cerata leaflike (broad in the middle and tapering toward both ends), distinctly flattened in cross section; with a prominent oral veil on the head | 4 |
| 3a | Body whitish, translucent, without blue spots on the dorsum; with an irregular dorsomedial red band (this may be interrupted) running from in front of the rhinophores to near the last pair of cerata; crest between the rhinophores distinctly red; terminal portions of cerata with a proximal orange band followed by a transparent colorless band and finally by an opaque white tip | Janolus fuscus |
| 3b | Body whitish, translucent, with small (visible with magnification) blue spots scattered over the dorsum; without a dorsomedial red line; crest betewen the rhinophores sometimes pale orange but not red; terminal portions of cerata with a proximal orange band succeeded by white, or with an orange band succeeded by white bands and finally by blue bands | Janolus barbarensis |
| 4a | Body orange, with white splotches on the dorsum (with white lines on the eges of the cerata, but not around the foot and oral veil, or between the rhinophores) | Dirona aurantia |
| 4b | Body not orange, and without white splotches on the dorsum | 5 |
| 5a | Cerata smooth, each bordered by a white line; body usually whitish, translucent (some specimens are mauve, and occasionally the cerata are pinkish); with white lines around the edge of the foot and oral veil, as well as between the rhinophores | Dirona albolineata |
| 5b | Cerata usually roughened, each with a pale red spot, but not bordered by a white line; body light brown to greenish gray, with small yellowish, greenish, and pink dots; without white lines around the edge of the foot and oral veil, or between the rhinophores (not likely to be found north of Oregon) | Dirona picta |
Armina californica
Dirona
albolineata
Dirona aurantia