Fig. 2. Kinematic identification of the two most frequently observed elements of the larval locomotor repertoire, scoots and routine turns. (A) Example of a scoot, showing the low bend angle and forward trajectory of the larva. (B) Example of a routine turn, demonstrating the large bend angle and reorientation of the larva prior to forward swimming. (C) Histogram of bend amplitudes for 4199 movement events. The histogram was fitted as the sum of two Gaussians (solid black line: for peak 1, µ=16.9, =7.9; peak 2, µ=59.6, =20.1). (D) Scatter analysis of bend angles against bend amplitudes for 1681 movement episodes confirms spontaneous motor events do not form a behavioral continuum, but can be distinguished by selecting thresholds for bend amplitudes and angles. Red dotted line indicates the amplitude and head bend angle thresholds used to distinguish scoots from turns. (E–J) Kinematic analysis of the two types of movement events distinguished in D (672 scoots, 1009 turns) verifies that this method identifies motor patterns with distinct properties. Kinematic distributions for trajectory (E), displacement (F), head bend angle for the second sinusoid, equivalent to the `counterbend' for turns (G), bend amplitude for the counterbend (H), swim yaw (I) and swim rhythm (J) show highly significant differences (independent sample t-test with unequal variances, P<10^–10).