Nudibranchs (Opisthobranchs)

Order Nudibranchia

Suborder Aeolidina & Arminina

Suborder Arminina
This is the smallest suborder of nudibranchs and includes the remaining Nudibranchia
which don't quite fit into the other categories.


Suborder Aeolidina
This group has clusters or rows of long, finger-like cerata.
Many are prey specific which creates fluctuations in their
populations and locations as they follow their prey.

 Flabellina verrucosa
photographed intertidally
Flabellina verrucosa
(Johnson, 1832)

Red-gilled Nudibranch
intertidal to 300m          size to 10cm
northern Washington to southern Alaska and
circumboreal, Sea of Japan and North Atlantic
This species is infrequently found intertidally.

Flabellina trophina Flabellina trophina
photographed subtidally
Flabellina trophina
(Bergh, 1894)

Long-mouthed Aeolid
subtidal to 65m          size to 50mm
central Oregon to southern Alaska; Sea of Japan

This species has a pronounced pointed snout and the cerata are
continuous along its back instead of in clusters.
(synonym - Flabellina fusca)
Flabellina trilineata
photographed subtidally
Flabellina trilineata (O'Donoghue, 1921)
Three-lined Aeolid
intertidal to 50m          size to 36mm
northern Mexico to southern Alaska
This is infrequently found intertidally.  It is distinguished
by it's orange tipped cerata and rhinophores and by the
three white lines extending the length of the body.
(previous name - Coryphella trilineata)

Cerberilla mosslandica
photographed subtidally
Cerberilla mosslandica

McDonald and Nybakken, 1975
Moss Landing Aeolid
subtidal          size to 9mm
southern California to southern BC
This species burrows in soft sediments.

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This page last revised: 11-17-2012
Hermissenda crassicornis Hermissenda crassicornis Hermissenda crassicornis
                photographed subtidally                                    photographed intertidally                             photographed subtidally
Hermissenda crassicornis (Eschscholtz, 1831)
Opalescent Nudibranch *
intertidal to 37m     northern Mexico to central Alaska; Sea of Japan     size to 8cm
This species is occasionally found intertidally.  It has a distinctive bright orange stripe on its head.
Aeolidia papillosa Aeolidia papillosa Aeolidia papillosa
 all photographed intertidally
Aeolidia papillosa (Linnaeus, 1761)

Shag-Rug Nudibranch *
intertidal to 900m          northern Mexico to central Alaska; Sea of Japan; circumboreal;
and southern South America on both coasts               size to 10cm
This species is occasionally seen intertidally.
 It has the unique characteristic of storing the stinging cells, from the anemones it feeds on, in its cerata for its own defense.

Janolus fuscus Janolus fuscus Janolus fuscus
                  photographed intertidally                      photographed subtidally
Janolus fuscus (O'Donoghue, 1924)
White-and-Orange Tipped Nudibranch
intertidal to 30m          size to 25mm
southern California to southern Alaska; Sea of Japan
This is infrequently found intertidally. Look in tidepools or shallow water.
Dirona albolineata Dirona albolineata Dirona albolineata
     photographed intertidally                photographed subtidally
Dirona albolineata MacFarland, 1905
Frosted Nudibranch *
intertidal to 37m          size to 18cm
southern California to southern Alaska; also Japan & Siberia
It is occasionally found intertidally. Look in tidepools under plants.
 The cerata can be white, salmon or purplish in color.
Armina californica Armina californica all photographed subtidally                                     attacking sea pens
Armina californica
(Cooper, 1963)

Striped Nudibranch
intertidal to 230m on sandy bottoms          Panama to northern Alaska          size to 7cm
This species is infrequently found intertidally in the northwest.

Cuthona concinna
photographed subtidally
Cuthona concinna

(Alder & Hancock, 1843)
Neat Aeolid
subtidal          size to 15mm
southern BC to northern Alaska; circumpolar
This is a very plain species
and may be cream to yellow.
(previous name - Trinchesia concinna)

Catriona columbiana
photographed subtidally
Catriona columbiana

(O'Donoghue, 1922)
British Columbia Aeolid
intertidal to subtidal          size to 20mm
southern California to southernmost Alaska;
South Africa; New Zealand; Japan
This species is very infrequently seen
intertidally.  It feeds on the hydroid Tubularia.
(synonyms - Catriona alpha, Cratena spadix)

Click on photo to enlarge.  Scale line in photo equals 1cm unless otherwise specified.
* Species which are the most commonly encountered nudibranchs on the beach.

Those in the order Nudibranchia are the true sea slugs.  The adult forms have a complete absence of a shell and have externally exposed respiratory organs.  

Dirona pellucida
photographed subtidally
Dirona pellucida
Volodchenko, 1941

Translucent Dirona
intertidal to subtidal          size to 12cm
central Oregon to northern Alaska;
Sea of Japan to Russia

This is infrequently found intertidally.  
White speckling on the lower body
distinquish it from D. albolineata.
(synonym - Dirona aurantia)

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