Intertidal Invertebrates of the Monterey Bay Area, California

Compiled & photographed by Gary McDonald, Long Marine Laboratory, University of California, Santa Cruz

Hermissenda crassicornis (Eschscholtz, 1831)
Opalescent Nudibranch
Mollusca: Gastropoda: Opisthobranchia: Nudibranchia: Aeolidina: Facelinidae
Geographic Range: Kodiak Island, Alaska, to Bahia de Los Angeles, Baja California, Mexico; Japan. Synonyms: Hermissenda opalescens, Phidiana crassicornis.
Back to: .Aeolidina Back to: Intertidal Invertebrates of the Monterey Bay Area
Carmel Pt., Monterey Co., CA; 23 Nov 2007; 20mm total length.

Description: Ground color translucent greyish-white. A median band of brilliant cadmium orange occurs between oral tentacles and passes between rhinophores (where it is narrowest), to anterior of cardiac region; an opalescent blue line occurs dorsally on either oral tentacle, becoming broader & bifurcating proximally, inner portion of blue line extends between rhinophores, on either side of orange line, and continues dorso-medially to tip of tail; outer portion of these blue lines extend dorso-laterally to tip of tail. A narrow, opalescent blue line extends posteriorly along dorsal margin of foot, from foot corners to tip of tail. Cerata in 5-11 groups, tipped with white, with a subterminal band of cadmium orange, cores usually light burnt umber to deep brown, but variable depending upon food source. Occasional individuals may have cerata with reddish-orange tips, & a bluish-white band longitudinal on anterior surface of each ceras (more common in northern part of range). Rhinophores weakly perfoliate, with 8-24 lamellae, clavus opalescent white to very pale blue. May be distinguished from the much rarer Emarcusia morroensis which has smooth rhinophores and lacks opalescent blue lines on body
Size: Typically about 25mmm in length, but may exceed 70mm.
Notes: Feeds on a variety of hydroids.

Pigeon Pt., San Mateo Co., CA; 18 Feb 2008; 39mm total length.
Pigeon Pt., San Mateo Co., CA; 18 Feb 2008; 39mm total length
Pigeon Pt., San Mateo Co., CA; 26 Oct 2007; 55mm total length.
Carmel Pt., Monterey Co., CA; 25 Nov 2007; ~20mm total length.
Carmel Pt., Monterey Co., CA; 9 Apr 2008; 25mm total length.
Scott Cr., Santa Cruz Co., CA; 9 May 2008; 45mm total length.
Asilomar, Monterey Co., CA; 4 June 2008; 3mm total length.
Carmel Pt., Monterey Co., CA; 9 Apr 2008; 20mm total length.

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