Editing Sea butterfly (section)

=== Swimming kinematics ===
Molluscan pteropods develop their feet into a pair of wing-like parapodia in the growing phase. These 'wings' are highly flexible, as the orientation of the muscles is different, and they have a [[hydrostatic skeleton]] filled with a pressurized fluid. Thus, the high bending-angle supports the parapodia to diminish the [[Drag (physics)|drag forces]] generated by the classic "[[Insect flight|clap-and-fling]]" maneuver; additionally, it aids in carrying the extra weight of a shell and ascending the water column for the [[diel vertical migration]].<ref>Karakas, F., Maas, A. E., & Murphy, D. W. (2020). A novel cylindrical overlap-and-fling mechanism used by sea butterflies. Journal of Experimental Biology, 223(15), jeb221499.</ref>

The power-stroke for ''L. helicina'' starts with a sharp rotation of it is body accompanied by an increase in swimming speed; it then rotates its shell in the opposite direction to initiate the recovery-stroke and swims upward, with a speed less than the power phase. There is a drop in overall speed between power and recovery strokes, which develop a [[Sawtooth wave|sawtooth]] trajectory in the [[sagittal plane]]. The hyper-pitch of the round shell of ''L. helicina'' diminishes the rotational drag and the moment of [[inertia]]; the extreme shell rotation also assists in raising the wingtips at the end of each stroke to create a figure-eight pattern, common for [[Pterygota|flying insects]]. In contrast, flying insects and shell-less pteropods encounter higher resistance forces that limit the body rotation.<ref>Murphy, D. W., Adhikari, D., Webster, D. R., & Yen, J. (2016). Underwater flight by the planktonic sea butterfly. Journal of Experimental Biology, 219(4), 535-543.</ref>  

Sea butterflies range from the tropics<ref name=ParraFlores2009/> to the poles.<ref name=Seibel2007/>
They are "[[holoplankton]]ic"—they spend all their lives floating amongst [[plankton]], rather than remaining planktonic during their [[larva]]l stage.{{efn|Compare the sea butterflies unusual whole-life residence in the [[plankton]] with the more common behavior of most other [[marine (ocean)|marine]] gastropods, whose [[veliger]] larvae are part of the [[meroplankton]], but who leave the plankton once they reach adult form.}} Thus, thecosomans are most common in the top {{Convert|25|m}} of the ocean—in terms of diversity, species richness, and abundance—and become scarcer with increased depth.<ref name=ParraFlores2009>
{{cite journal
 |author1 = Parra-Flores, A.
 |author2 = Gasca, R.
 |year = 2009
 |title = Distribution of pteropods (Mollusca: Gastropoda: Thecosomata) in surface waters (0–100&nbsp;m) of the Western Caribbean Sea (winter, 2007)
 |journal = Revista de Biología Marina y Oceanografía
 |volume = 44  |issue = 3  |pages = 647–662
 |doi = 10.4067/s0718-19572009000300011  |doi-access = free
}}
</ref>

Occasionally, thecosomans swarm in large numbers, and can sometimes be found washed ashore in [[flotsam]], especially along the coastline of [[eastern Australia]].