| 1a |
With an external shell large enough to accommodate all ( or nearly
all) of the animal when it withdraws |
2 |
| 1b |
Either without an external shell, or with a shell that is only partly
visible externally and that cannot accommodate more than a small part of
the animal |
4 |
| 2a |
Shell coiled sinestrally,
but otherwise shaped much like that of Tegula,
Margarites
and other trochid
prosobranchs (pelagic; swimming with oarlike flaps of the much modified
foot) |
Order Thecosomata:
Limacina helicina |
| 2b |
Shell either not coiled or coiled dextrally,
and not shaped like that of a trochidprosobranch |
3 |
| 3a |
Shell either slender and with a whorl,
spire
taller than the body or more or less ovoid, or (in Cyclostremella)
planispiral
and with the diameter greater than the height; aperture
not more than half the height of the shell (except in Cyclostremella) |
Order Pyramidellacea |
| 3b |
Shell either nearly cylindrical and with a short spire
or no visible spire,
or narrowly ovoid; aperture
at least slightly more than half the height of the shell, and sometimes
equal to the height |
Order
Cephalaspidea
(in
part) |
| 4a |
Pelagic; part
of the mantle, just
behind the head, elaborated into flipperlike structures used for swimming |
Order Gymnosomata |
| 4b |
If pelagic, only temporarily so; lateral extensions of the body, if
present, forming sheetlike flaps along much of the length of the foot,
and not primarily for swimming |
5 |
| 5a |
With a single gill, this located on the right side of the body, between
the overlapping mantle
margin and the foot [Notaspidean, also called sidegill slugs, have a series
of feather-like gills on the right side below the mantle. They have
rolled rhinophores. Some such as Tylodina have an external
shell, while in others such as Berthella
the shell forms a thin, inconspicuous plate. Most species are nocturnal.]
[Was identified as Berthella californica in original key] |
Order Notaspidea:
Berthella
chacei |
| 5b |
With or without gills, but not with a single gill located on the right
side of the body between the overlapping mantle
margin and the foot |
6 |
| 6a |
With a gill chamber (its length about one-fifth the length of the body)
located about halfway back on the dorsum,
just to the right of the midline ( with black longitudinal stripes on a
green or yellow-green background) |
Order Anaspidea:
Phyllaplysia
taylori |
| 6b |
Without a gill chamber on the dorsum (none of the species in our region
has longitudinal black stirpes on a green or yellow-green background) |
7 |
| 7a |
Shell present, although it may be small and delicate and partly or
completely hidden by the mantle;
cephalic
shield present; fleshy lateral outgrowths of the mantle
turned up dorsally but overlapping one another only slightly, if at all. |
Order
Cephalaspidea
(in
part) |
| 7b |
Shell absent; cephalic
shield absent; lateral outgrowths of the body, if present, forming
sheetlike flaps along much of the length of the foot, and if turned up
dorsally, overlapping one another to a considerable extent |
8 |
| 8a |
Small (maximum length 3 or 4 mm); living in sand, visceral mass distinct
from head and foot, and extending posteriorly beyond the foot |
Order Acochlidiacea |
| 8b |
Not especially small (commonly more than 3 or 4 mm long, except when
young); not living in sand; visceral mass not distinct from the head and
foot, and not extending posteriorly beyong the foot |
9 |
| 9a |
With a lung, whose opening is on the posteroventral side of the mantle
immediately behind the anus (photo);
eyes at the tips of distinct stalks (photo) |
Subclass
Gymnomorpha,
Order
Onchidiacea:
Onchidella
borealis |
| 9b |
Without a lung; eyes not at the tips of stalks |
10 |
| 10a |
Rhinophores
absent [Sacoglossans are mostly small, greenish herbivores, though some
species feed on opisthobranch eggs. Some have shells, while others
have no shells but have ridges, folds, or papilli on the back. Most
have rolled, tube-like rhinophores] |
Order Sacoglossa
(in part) |
| 10b |
Rhinophores
present |
11 |
| 11a |
Clavus of
rhinophores perfoliate,
or with longitudinal ridges, or with vertical pinnate
plumes beside the clavus |
Order
Nudibranchia
(in
part) |
| 11b |
Clavus of rhinophores
smooth and not distinct form the stalk (in cross-section, the rhinophores
may be solid or rolled into cylinders) |
12 |
| 12a |
Rhinophores
retractile into sheaths |
Order
Nudibranchia
(in
part) |
| 12b |
Rhinophores
not retractile into sheaths |
13 |
| 13a |
Dorsum with elongate
outgrowths, such as cerata |
14 |
| 13b |
Dorsum without
elongate outgrowths. |
Order Sacoglossa
(in part) |
| 14a |
Rhinophores
rolled into cylinders. |
Order Sacoglossa
(in part) |
| 14b |
Rhinophores
solid in cross-section |
15 |
| 15a |
Anus on the midline, just posterior to the rhinophores |
Order Sacoglossa
(in part) |
| 15b |
Anus on the right side of the body |
Order
Nudibranchia
(in
part) |