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
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.
Some species in this order have vestigial shells.
Hermaeidae photographed subtidally
Hermaea oliviae (MacFarland, 1966)
northern Mexico to southern BC size to 10mm
small size makes it difficult to find. Search for it on
filamentous green algae. The body is decorated with mahogany
(previous name - Aplysiopsis oliviae)
Limapontiidae found intertidallyOlea hansineensis Agersborg, 1923Hansine's Egg Eatersouthern California to southern Alaska size to 13mmThis 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.
Plakobranchidae photographed subtidally photographed subtidallyPlacida dendritica (Alder & Hancock, 1843)
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 (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 Shellintertidal
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 Aglajavery shallow subtidal to 20m on mud bottoms size to 20mmsouthern California to southern AlaskaIt 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
Cylichnidae 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
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.
Gastropteridae all photographed subtidally
Diaphanidae photographed subtidallyDiaphana californica Dall, 1919California Diaphana
intertidal to shallow subtidal size to 5mm
northern Mexico to northern Washington
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.
photographed subtidally Gastropteron pacificum Bergh, 1894Pacific Stomach Wingintertidal to 425m size to 40mmnorthern Mexico to northern Alaska; GalapagosThis 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.) photographed subtidallyMelanochlamys 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.
Order Sacoglossa, Cephalaspidea
& Family Acteonidae