Abstract
A compendium of the northeast Pacific benthic shelled sea slugs formerly classified in the paraphyletic group “Opisthobranchia” is provided. These include organisms with internal and/or reduced shells. Shell-less groups such as Nudibranchia or closely related benthic shelled clades such as the Pyramidelloidea and the Siphonarioidea are excluded. The Sacoglossa is not represented by any shelled forms in the northeast Pacific and therefore is also excluded. Descriptions include diagnostic characteristics, species abundance information, geographic and bathymetric ranges, and ecological data (if available). Short remarks for most species and higher taxa provide additional information published elsewhere and/or address outstanding taxonomic or nomenclatural issues. Illustrations of the shells and — in some cases — the live animals are provided. Species are arranged based on current classification schemes and a full list of primary synonyms, location of type material (if known), and type localities of all synonyms are provided for each species. Three new species are described in this paper: Microglyphis michelleae new species, Microglyphis sabrinae new species and Bogasonia jennyae new species. Oscaniella purpurea Bergh, 1897 is here designated the type species of Oscaniella Bergh, 1897
