In this clade, the foot of the gastropod has developed into wing-like flapping appendages (parapodia) and larval sea angels discard their embryonic shells a few days after hatching.

The lack of a heavy shell for gymnosomes allows them to hover on the upper water surfaces for longer periods, along with a streamlined body that reduces the drag coefficient.

[3] Sea angels are gelatinous, mostly transparent, and very small, with the largest species (Clione limacina) reaching 5 cm.

[2] Their lifestyles have coevolved with those of their prey, with their feeding strategy adapting to the morphology and consistency of the thecosome shell.

Tracing the wingtip showed a ‘figure-of-eight’ trajectory and stroke plane orthogonal to the caudal-rostral axis, this pattern was observed in some aerial insects, small birds, and sea butterflies such as hummingbirds and Limacina helicina.

[7] Furthermore, Clione antarctica, defends itself from predators by synthesizing a previously unknown noxious molecule, pteroenone.

Local population density of C. antarctica may reach extraordinary levels; up to 300 animals per cubic metre have been recorded.

Also, the increment in the angle of attack along with low Reynold number for sea angels resembles the fluid dynamic forces acting on insects such as Drosophila.

[8] Gymnosomes slowly beat their wing-like parapodia[2] in a rowing motion[9] to propel their "perfectly streamlined"[9] bodies through the upper 20 m of the water column.

[11] Clione antarctica Pneumodermopsis spe Spongiobranchaea australis Pneumoderma violaceum (19 species in 13 genera) The other suborder of pteropods, Thecosomata, is superficially similar to sea angels, but are not closely related; some authorities include both Thecosomata and Gymnosomata as separate branches of the order Pteropoda, whereas others list them as distinct orders within the subclass Heterobranchia.