Helical swimming and body reversal behaviors in Lumbriculus variegatus (Annelida: Clitellata: Lumbriculidae)

Two unusual locomotor behaviors (body reversal and helical swimming) are described and related to postembryonic body size in the freshwater oligochaete, Lumbriculus variegatus (Annelida: Clitellata: Lumbriculidae). Both behaviors occur as responses to tactile stimulation when worms are on smooth substrates that offer little or no traction or protection. Body reversal, evoked by touch to anterior segments, involves a stereotyped sequence of bending movements that effectively reverse head and tail positions in about 0.4 s in newly hatched worms and 0.6 s in juvenile and adult worms. Though little net shift in the body center occurs, reversal may optimize body positioning in preparation for swimming away from predatory threat. In contrast to reversal, swimming is evoked by touch to posterior segments and consists of a rapid, rhythmic sequence of helical body waves (frequency [asymptotically =] 9-11 Hz). Waves alternate between clockwise and counterclockwise helical orientations, with posterior passage of each wave providing forward thrust. Swim velocity and wave velocity increase with body size. Though total distance and duration of each swim episode is short ([asymptotically =] 1-2 body lengths in < 2 s), swimming may be an important means of predator avoidance in the littoral environment of these worms.[PUBLICATION ABSTRACT]