A kinematic analysis of tentacle extension in the squid Loligo pealei

High-speed cine recordings of prey capture by the squid Loligo pealei were used to analyze the kinematics of the rapid tentacular strike. The proximal portion of the tentacle, the stalk, elongates during the strike. The non-extensible distal portion of the tentacle, the club, contacts the prey and attaches using suckers. Seven sequences of prey capture filmed at 750 frames s-1 were analyzed frame by frame. The positions of the head, the tentacles and the prey were digitized, and the data were smoothed using quintic natural B-splines and the generalized cross-validation (GCV) criterion. During the strike, the animal swims forward at velocities ranging from 0.7-1.2 m s-1, and as the eight arms are flared, the tentacular stalks elongate. Tentacular extension occurred in approximately 20-40 ms with peak strains in the tentacular stalk ranging from 0.43-0.8. Peak longitudinal strain rates varied from 23-45 s-1. Maximum extension velocities of the stalk were calculated to be over 2 m s-1 with peak accelerations of approximately 250 m s-2. Once the tentacular clubs have contacted the prey, the tentacular stalks are frequently observed to buckle.