Jet propulsion at the smallest size scales: Kinematics and fluid dynamics of swimming Siphonophores

Siphonophores (Cnidaria: Hydrozoa) inhabit pelagic waters where representative species occupy depths ranging from the surface to the abyss. Locomotion by siphonophores is achieved by nectophore muscular contractions, which generate vortex ring wakes similar to jet-propelled medusa and squid. Using high-speed video analysis, we compare the kinematics and characterize wake structures of two different species of siphonophores during straight and turning swimming. By extracting the kinematics of individual nectophores, we quantify the formation time (T*) to characterize the jet wake. We show the T* generated by swimming physonect siphonophores are larger than other jet-propelled swimmers.