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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 ten orders that have been found in Hawaiian waters:
Acteonoidea, Cephalaspidea, Runcinida, Thecosomata, Gymnosomata,
Anaspidea, Sacoglossa, Umbraculoidea, Pleurobranchomorpha and
Nudibranchia. Two orders, the Rhodopemorpha and Acochlidimorpha have
often been placed in the Opisthobranchia. However, Bouchet, et. al., 2017 places them, respectively, with the Lower Heterobranchs
and marine Pulmonates. Both
include small worm-like species that live interstitially in sand or in
algal turf. 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.
To see a page with 40 commonly seen species, click here. To see a page with 40 common
species (not the same thing at all), click here.
To see a list of recent changes, click
here.
|
 Acteonoidea |
 Cephalaspidea |
 Runcinida |
 Thecosomata |
 Gymnosomata |
 Anaspidea |
 Sacoglossa |
 Umbraculoidea |
 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 58% 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 |
 marginellids & cysticids |
 aceolomorph flatworms |
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 |
| Thumbnails |
Species list |
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