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Opisthobranchia
| The
subclass Opisthobranchia includes gastropod mollusks
that have
bilateral symmetry and a tendency toward reduction
or
loss of the shell. There are nine orders that have
been found in
Hawaiian waters: Acteonoidea, Cephalaspidea,
Thecosomata, Gymnosomata,
Anaspidea,
Sacoglossa, Tylodinoidea, Pleurobranchomorpha and
Nudibranchia. Two
orders, the
Acochlidea and Rhodopemorpha, have not been recorded
from Hawaii.
However, they include small worm-like species that
live interstitially
in sand or in algal turf so could easily have been
missed. For the
number of known species in each group see: table. To
display thumbnail
images of all the Hawaiian sea slugs on one page
for quick
identification, click
here.
|
 Acteonoidea |
 Cephalaspidea |
 Thecosomata |
no photo available Gymnosomata |
 Anaspidea |
 Sacoglossa |
 Tylodinoidea |
 Pleurobranchomorpha |
 Nudibranchia |
|||
Order Nudibranchia
| The order
Nudibranchia
includes species that lack shells and have various
forms of secondary
gills. All are carnivores. It is divided into four
suborders:
Doridacea,
Dendronotacea, Arminacea, and Aeolidacea. Hawaiian
nudibranchs
represent about 57% of the opisthobranch species
found in the islands. |
Doridacea |
 Dendronotacea |
 Arminacea |
 Aeolidacea |
Opisthobranch Look-alikes
| Several
other taxa are often mistaken for opisthobranchs.
The following links
provide a brief treatment of the most common as an
aid to
identification. |
 sea cucumbers |
 flatworms |
 velutinids |
 cowries & relatives |
 onchidiids |
 galeommatids |
 benthic ctenophores |
 polychaetes |
___________________________________________
Opisthobranch relatives
| Several families
usually
listed as prosobranchs and currently placed in the
lower Heterobranchia
(previously Heterostropha) have
been considered part of the Opisthobranchia or
closely related to them
in the past. The following links provide a brief
treatment of some of
these families. |
| |
 Pyramidellidae |
 Architectonicidae, etc |
|
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