Gymnosomata (often referred to as "sea angels") includes specialized pelagic predators that lack shells
and use an expanded portion of the foot for swimming. Most have
elongate bodies. Recently, some sources have recombined them with the Thecosomata under the Pteropoda (known as "sea butterflies").
Little is known about the Hawaiian fauna. In addition to Cliopsis krohni, four other species have been
recorded from the north Pacific near Hawaii.
Thliptodon diaphanus (Meisenheimer, 1903) in the family Clionidae
was photographed off Kona, Big Island by Boz Johnson during a black
water dive. The photo, posted to the Blackwater Photo Group on Dec. 28,
2021, can be seen here.
Three other species have been collected in the general vicinity of Hawaii based on the range maps in Pelagic
Molluscs on the Marine
Species Identification Portal:
(Rang, 1825) in the family Hydromylidae
Pelseneer, 1887 in the family Notobranchaeidae
(Gegenbaur, 1855) in the family Pneumodermatidae