power strokes by the four or five thoracic legs followed by a tail flap, moving the
animal into the range of inertial drag, and coasting during return of the legs anteriorly,
decelerating it back toward the viscous drag of low Reynolds numbers. In C.
finmarchicus C5, the cycling of escape velocities is zero to 750 cm s−1 in 8 ms,
dropping to ∼380 cm s−1 in the next 4 ms, with acceleration pulsing greatly with the
power stroke of each successive leg (Fig. 8.15).
Fig. 8.15 Dynamics of escape swimming in C. finmarchicus. (a) Velocity build-up and
fall-off as a free-swimming individual rows (cope-pod is from Greek for “oar-foot”)
with sequential rearward sweeps of its five thoracic legs (P5 at the rear first, P4, ... ,
P1), but then must be slowed by drag as the legs return anteriorly, feathered. Setae
open flat on the power stroke, close and trail on the return. (b) The acceleration
sequence showing successive responses to the serial leg sweeps. An escape jump
involves multiple power and recovery cycles.
(^) (From Lenz et al. 2004.)
(^) If this suite of tricks did not work some of the time, then extinction would follow.