Nudibranchs - Cephalaspidea, Gymnosomata, Thecosomata

Order Cephalaspidea
This order is distinguished by the presence of a head shield on the animal. Although several of these species have a shell, they are actually opisthobranchs (sea slugs). They are commonly referred to as Bubble Shells. Many identification books group them with the gastropods to make identifying them easier. Some of the species in this group have a vestigial shell inside the mantle which is not visible.

Rictaxis punctocaelatus (Carpenter, 1864)
Striped Barrel Shell
intertidal to 100m northern Mexico to southermost Alaska size to 20mm
This is infrequently found intertidally in the northwest. It lives on sand and glides just
underneath the surface of the sediment, usually just below eelgrass beds.

These are very small shells and can be difficult to spot. In the right habitat, the shells can generally be found by sifting through the sand at low tide near the water.

photographed intertidally

Haminoea vesicula Gould, 1855
White Bubble Shell
intertidal to shallow subtidal on eelegrass and mud in sheltered bays
northern Mexico to southern Alaska size to 24mm

Acteocina eximia (Baird, 1863)
Pleatless Barrel-Bubble
intertidal to subtidal on sand and mud
shell size to 13mm
from central California to central Alaska
(In some references it is considered a
subspecies of A. culcitella)

Haminoeidae

Haminoea japonica (Pilsbry, 1895)
Oval Bubble Shell
intertidal on eelgrass and sand San Francisco Bay, California; northern Washington to southern BC; Japan size to 35mm
This is found only in the locations where it has been introduced and is often alongside H. vesicula. The shells are very similar. On the live animal, H. japonica has a deeply bifurcate cephalic shield.
(previously called Haminoea callidegenita when found in the eastern Pacific)

Aglajidae

photographed right at the water's edge
Aglaja ocelligera (Bergh, 1894)
Spotted Aglaja
very shallow subtidal to 20m on mud bottoms
size to 20mm
southern California to southern Alaska
It has a vestigial internal shell. This is a small species and while it is normally subtidal, it is possible to find it on a very low tide near the water's edge. This photo was taken when a small group of the animals were spotted at the base of eelgrass in a couple inches of water at low tide.

Haminoea virescens (Sowerby, 1833)
Green Bubble Shell
intertidal on rocky, open coast habitat
Panama to Alaska size to 18mm

Cylichnidae

Acteocina culcitella (Gould, 1852)
Western Barrel-Bubble
intertidal to 46m on sand and mud
shell size to 22mm
from northern Mexico to central Alaska
(previous name - Cylichnella culcitella)

Gastropteridae

photographed subtidally
Gastropteron pacificum Bergh, 1894
Pacific Stomach Wing
intertidal to 425m size to 40mm
northern Mexico to northern Alaska; Galapagos
This is infrequently found intertidally. This species may be readily seen when
it is swimming. When buried in the sediment, it is a small lump in the mud.
(For more insight into this creature,
see Ron Shimek's Blog posting of August 8, 2011.)

Order Thecosomata
The members of this order are planktonic sea slugs. They possess a thin
external shell in most cases. The head is indistinct and the foot and tentacles are
rudimentary. Not all experts agree as to whether or not they are classified under
the opisthobranchs, but we group them here with the other sea slugs.

Order Gymnosomata
The members of this order are pelagic sea slugs. They possess a shell in
the larval stage but discard it at metamorphosis. The foot of the snail has
developed into a wing-like appendage, allowing the animal to swim.

Corolla spectabilis Dall, 1871
Spectacular Corolla or Sea Butterfly
pelagic size to at least 8cm
eastern Pacific Ocean; western Atlantic Ocean; Hawaii; Japan; Mediterranean Sea
This species "flies" through the water. Rather than an external shell, it possesses
a gelatinous internal pseudoconch. It can be very abundant in the water and occasionally the gelatinous pseudoconch can wash up on the beach.

Clione limacina (Phipps, 1774)
Sea Angel
pelagic to 600m size to 80mm
all northern cold and temperate seas, locally - northern Mexico to Arctic
This pteropod species swims through the water and can be very abundant.
It is carnivorous and feeds on other pteropods.

Haminoea vesicula is the most commonly found bubble shell in the Northwest. In sheltered areas, it can be abundant during the spring and summer while laying its eggs. The bright yellow egg ribbons are easy to spot among eelgrass and algae. Haminoea shells are very thin and fragile, and easily broken. For this reason, dead shells are not commonly found.

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.

Nudibranchs (Opisthobranchs)

Order Cephalaspidea, Gymnosomata

& Thecosomata