Key to Suborder Aeolidacea

Taken primarily and modified from  Kozloff, 1987, 1996  p. 255 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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1a	Each ceras with a sail-like ridge on its posterior side (the ridge begins near the base and runs for much of the length of the ceras) (length up to 2 cm)	Fiona pinnata
1b	Cerata without a sail-like ridge on the posterior side	2
2a	At least a few rows of cerata located anterior to the bases of the rhinophores	3
2b	None of the rows of cerata located anterior to the bases of the rhinophores (some may be at the same level as the rhinophores, however)	7
3a	Longest cerata more than half the length of the body; cerata usually oriented approximately at right angles to the anterior-posterior axis of the body; foot proportionately broad (usually less than 3 times as long as wide), tapering to a point at the tail	Cumanotus beaumonti
3b	Longest cerata less than one-third the length of the body; cerata usually oriented approximately parallel to the anterior-posterior axis of the body; foot relatively narrow (usually more than 4 times as long as wide), bluntly rounded at the tail	4
4a	Anterolateral corners of foot projecting as acute pedal tentacles (photo); body covered with gray to brown spots, these being most dense on the cerata (some specimens, especially from floats, lack pigment); usually with a prominent triangular white patch just anterior to the rhinophores; hepatic diverticula not clearly visible within the cerata of pigmented specimens; usually associated with anemones, especially Metridium and Anthopleura; length often attaining 5 cm	Aeolidia papillosa
4b
5a
5b
6a
6b
7a	Anterolateral corners of foot elongated, forming rather prominent tentacles	8
7b	Anterolateral corners of foot broadly rounded or somewhat triangular, but not forming prominent tentacles	13
8a	Basic body color purple; rhinophores and cerata bright orange for their entire length	Flabellina iodinea
8b	Basic body color not purple, usually translucent white or grayish; rhinophores and cerata not orange for their entire length (they may, however, be partly orange)	9
9a	With an orange band beginning just anterior to the rhinophores and passing between them, reaching the first group of cerata (a similar orange band may be present on the cardiac region); orange areas usually bordered by broad, opaque white or luminous blue dorsomedial lines that begin on the oral tentacles and continue to the tip of the tail; tips of cerata usually orange or chrome yellow, but with some white at the extremity. (Modified--All nudibranchs with this description were called Hermissenda crassicornis in the Kozloff key)	19
9b	Without orange bands on the dorsum; white lines on the dorsum, if present, not like 9a above--narrow and often interrupted; tips of cerata may be opaque white, but rarely orange	10
10a	With a dorsomedial white line (this may be interrupted or restricted to the tail region) or with 3 white lines, 1 dorsomedial and 2 lateral	11
10b	Without longitudinal white lines (rhinophores pale yellowish green distally; oral tentacles with opaque white dots)	20
11a	With 3 narrow white lines: 1 dorsomedial, running from the tip of the tail to just anterior to the rhinophores where it divides, 1 branch going to the tip of each oral tentacle; 1 on each side of the body just ventral to the cerata, beginning at the level of the first group of cerata and joining the dorsomedial line posterior to the last group of cerata.	Flabellina trilineata
11b	With a dorsomedial white line, this interrupted and often restricted to the tail region, but without lateral white lines	12
12a	Oral veil, between the oral tentacles, usually projecting dorsally as a blunt, triangular, median  papilla; tail short, blunt, extending just beyond the last group of cerata; pedal tentacles long; hepatic diverticula slender (less than one third the diameter of the cerata); white dorsomedial line extending from the tip of the tail to the most posterior group of cerata only; distal one-fourth of each ceras opaque white	Flabellina fusca
12b	Oral veil, between the oral tentacles, rounded, not projecting dorsally; tail long, slender, acute, extending one-third to one-half the total body length beyond the last group of cerata; pedal tentacles short; hepatic diverticula at least three-fourths the diameter of the cerata; white dorsomedial line extending from the tip of the tail to the rhinophores, although often interrupted; only the tips of the cerata opaque white.	Flabellina verrucosa
13a	Surface of cerata usually smooth; cerata may be held down on the body; cerata usually not inflated (or only slightly inflated), although in some species they may be rather flat, tapering from a wide central portion to a bluntly rounded tip; cerata not readily shed; hepatic diverticula, before ending the cerata, forming a neat symmetrical pattern, usually in transverse rows running across the body	14
13b	Surface of cerata slightly bumpy; cerata usually held erect; cerata cylindrical and slightly inflated in the central portion; cerata often shed when the animal is disturbed; hepatic diverticula, before entering the cerata, forming an irregular network	17
14a
14b
15a
15b
16a
16b
17a	Body pale translucent yellow-green with small specks of bown, black, and white; hepatic diverticula (including those in the cerata) greenish; usually with fewer than 15 cerata; associated with hydroids of the genus Obelia (E. olivaceous in Kozloff key)	Eubranchus rupium
17b	Body translucent white, sometimes with rust-brown splotches on the dorsum and cerata, and with small white spots on the cerata, rhinophores, and oral tentacles; hepatic diverticula not greenish (usually reddish or yellowish-brown); usually with more than 15 cerata; not associated with hydroids of the genus Obelia.	18
18a	With opaque white pigment on the tips of the cerata and often on the dorsum anterior to the region of the heart; hepatic diverticula red or reddish tan, giving the animal as a whole a reddish color; usually associated with the hydroid Sertularella tricuspidata	Eubranchus sanjuanensis
18b	With splotches of rust-brown pigment, as well as with opaque white pigment on the tips of the rhinophores and cerata and in a ring near the middle of each ceras (distal to the white ring is a subterminal ring of rust-colored spots; there is also a ring of rust-colored spots near the middle or beginning of the distal quarter of each oral tentacle and rhinophore); hepatic diverticula brown, sometimes with yellow spots; associated with the hydroid Plumularia lagenifera. Note: may have oral tentacles.	Eubranchus rustyus
19a	With a longitudinal white line running from the base to near the tip of the anterior side of each ceras. Found from Point Reyes, CA through Alaska	Hermissenda crassicornis
19b	Without a longitudinal white line running from the base to near the tip of the anterior side of each ceras. Found from Bodega Bay, CA south to the Sea of Cortez	Hermissenda opalescens
20a	Rhinophores pale yellow-green distally, cerata with subterminal band of rich brown. Hepatic diverticula within cerata deep olive to brownish-green.	Flabellina pricei
20b	Cerata cylindrical, inflated near the end, usually less than 15. Hepatic diverticula form an irregular network before entering the cerata and are green to olive-green within the cerata.  Body translucent yellow-green with small specks of brown, black, and white. Associated with hydroids of the genus Obelia. (Added to Kozloff key)	Eubranchus rupium

  Aeolidia papillosa
  Eubranchus rupium
  Hermissenda crassicornis
Hermissenda opalescens