An analysis of swimming behavior in the portunid crabCallinectes sapidus

The swimming behavior of a portunid crab was analysed using high‐speed cinematography. The posture adopted for sideways swimming includes the rigid extension of trailing legs 1–4 and the cyclic beating of the modified 5th‐legs. There is also beating of leading legs 2–4. The 5th‐legs beat in near synchrony at approx. 4/sec while legs 2–4 beat in a normal walking gait at approx. 2/sec. There is no significant phase coupling between legs 2–4 and the 5th legs. Amputation of single walking‐legs (2–4) causes the remaining 2 legs to beat alternately and phase relationships now appear between remaining walking‐legs and the 5th‐legs. Amputation of single 5th‐legs cause no changes in walking‐legs and bilateral amputation effects are also absent. These results lead to the postulation of neural control systems to account for the observed behavior.