title: Underwater flight by the planktonic sea butterfly.
abstract: In a remarkable example of convergent evolution, we show that the zooplanktonic sea butterfly Limacina helicina 'flies' underwater in the same way that very small insects fly in the air. Both sea butterflies and flying insects stroke their wings in a characteristic figure-of-eight pattern to produce lift, and both generate extra lift by peeling their wings apart at the beginning of the power stroke (the well-known Weis-Fogh 'clap-and-fling' mechanism). It is highly surprising to find a zooplankter 'mimicking' insect flight as almost all zooplankton swim in this intermediate Reynolds number range (Re=10-100) by using their appendages as paddles rather than wings. The sea butterfly is also unique in that it accomplishes its insect-like figure-of-eight wing stroke by extreme rotation of its body (what we call 'hyper-pitching'), a paradigm that has implications for micro aerial vehicle (MAV) design. No other animal, to our knowledge, pitches to this extent under normal locomotion.
authors.affiliation: School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355, USA dwmurphy@jhu.edu.
authors.forename: David W
authors.initials: DW
authors.lastname: Murphy
authors.affiliation: School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355, USA.
authors.forename: Deepak
authors.initials: D
authors.lastname: Adhikari
authors.affiliation: School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355, USA.
authors.forename: Donald R
authors.initials: DR
authors.lastname: Webster
authors.affiliation: School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230, USA.
authors.forename: Jeannette
authors.initials: J
authors.lastname: Yen
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D049851:Gastropoda / Q000033:anatomy & histology / Q000502:physiology*; D057446:Hydrodynamics; D013550:Swimming; D014921:Wings, Animal / Q000033:anatomy & histology / Q000502:physiology; D015048:Zooplankton
keywords: Convergent evolution; Insect flight; Pteropods; Swimming; Weis-Fogh mechanism; Zooplankton