Fig. 8.

Two modes of swimming in Aglantha digitale. (A) Video frames of an escape swim elicited by a glass probe used to disturb vibration receptors at the base of the tentacles. Time (ms) after stimulus is shown at the bottom of each frame. (B) Video frames at 0.1 s intervals of a single slow swim. Frames were captured at 1/300 s. (C) Changes in bell diameter over time. During an escape swim (top) the jellyfish bell contracts uniformly along its length; during recovery the base diameter (closed circles) recovers more rapidly than the mid-bell diameter (open circles). Data measured from individual video frames including those in A. During a slow swim (bottom) the change in diameter at the base of the bell (closed circles) is significantly less than that at the mid point (open circles). Data measured from individual video frames including those in B. Lines through the data drawn according to an equation for the performance of a damped oscillator: x=A₀exp^−bt(sin 2πt/τ), where x is the reduction in bell diameter, A₀ is the maximum diameter change in an un-damped system, b is the damping coefficient, t is time and τ is the period of the swim. Mid-way up the bell the values for A₀ are 0.675 (fast swim), 1.0 (slow swim); b is 0.0038 in each case; τ is 480 ms (fast swim), 1750 ms (slow swim). At the base of the bell, the values during the slow swim are 0.18 (A₀), 0.0038 (b), 1250 (τ). Temperature, 10°C. Data from R.W.M., unpublished results.