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Rictaxis punctocaelatus Rictaxis punctocaelatus

Order Cephalaspidea
Many species in this order have a shell, and are commonly referred to as Bubble Shells.  A few only have vestigial shells which are hidden inside the mantle.  Many identification books group the Bubble Shells with the gastropods to make identifying them easier.  

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.

This family is still under study and is not yet
assigned to one of the Opisthobranch orders.

Order Sacoglossa
  Some species in this order have vestigial shells.

Hermaea oliviae
photographed subtidally

Hermaea oliviae (MacFarland, 1966)
Olivia's Sapsucker
northern Mexico to southern BC          size to 10mm
Its small size makes it difficult to find.  Search for it on filamentous green algae.  The body is decorated with mahogany colored lines.
(previous name - Aplysiopsis oliviae)

Olea hansineensis
found intertidally
Olea hansineensis Agersborg, 1923
Hansine's Egg Eater
southern California to southern Alaska     size to 13mm
This specimen was found feeding on Haminoea vesicula eggs.
This species is very small and hard to spot.
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.

Elysia hedgpethi
photographed subtidally

Haminoea vesicula Haminoea vesicula Haminoea vesicula
                                                              photographed intertidally, with eggs               photographed intertidally
Haminoea vesicula Gould, 1855
White Bubble Shell

intertidal to shallow subtidal          northern Mexico to southern Alaska          size to 24mm
This is the most commonly found bubble shell in the Pacific Northwest.  It lives on eelegrass and mud in sheltered bays.  It can be very abundant during spring and summer while laying its eggs.  The bright yellow egg ribbons are easy to spot.  The shells are thin and fragile and break easily once the animal dies.  For this reason, dead shells are not commonly found.

Placida dendritica
photographed subtidally
Placida dendritica (Alder & Hancock, 1843)
Branched Sapsucker
central Mexico to Alaska          size to 8mm
Its small size makes it difficult to find.  The light colored body is marked with branching greenish lines.

Acteocina eximia
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)

Haminoea japonica Haminoea japonica
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)

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Aglaja ocelligera
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.
This page last revised: 3-16-2014
Haminoea virescens

Acteocina culcitella
Acteocina culcitella (Gould, 1853)
Western Barrel-Bubble
intertidal to 46m on sand and mud  
shell size to 22mm
from northern Mexico to central Alaska

(previous name - Cylichnella culcitella)

Elysia hedgpethi Marcus, 1961
Hedgpeth's Sapsucker
intertidal to shallow subtidal          size to 35mm
northern Mexico to southern BC
It is infrequently seen intertidally.  It is
well-camouflaged on the dark plants it prefers.

Gastropteron pacificum Gastropteron pacificum Gastropteron pacificum 
all photographed subtidally


Diaphana californica
photographed subtidally
Diaphana californica Dall, 1919
California Diaphana
intertidal to shallow subtidal          size to 5mm
northern Mexico to northern Washington
This is rarely found intertidally, partly due to its small size.  The shell is extremely thin and is similar in shape to the other bubble shells, but with a flat apex.  The animal is white.

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

Gastropteron pacificum
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.)

Melanochlamys diomedea
photographed subtidally
Melanochlamys diomedea (Bergh, 1893)
Diomedes' Aglaja
intertidal to113m          size to15mm
southern California to Alaska
It has a vestigial internal shell.  It is very similar in appearance to Aglaja ocelligera, but without the white spots.  It is light cream with brown and black mottling which can completely hide the cream color.
(previous names - Aglaja diomedea, Aglaja nana, Aglaja ezoensis)

 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 Sacoglossa, Cephalaspidea

& Family Acteonidae