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Metachronal exopodite beating in the mysid Praunus flexuosus: a quantitative analysis

The exopodite beating of Praunus flexuosus has been analysed from highspeed photographic records with the use of computer-assisted techniques. Limbs beat with a modified rowing action (figures 2, 3), and follow elliptical paths which facilitate an overlapping sequence of movement (figures 3, 4). Analysis of key temporal parameters indicates that beating occurs within a restricted range of frequencies around 4 Hz (table 1). Each beat cycle is composed of a powerstroke (p. s.), returnstroke (r. s.) and pause (p.), the r. s. being of constant duration in all exopodites (figure 5). P. s. and p show rostrocaudal gradients such that the p. s. is of longer duration and p. shorter in more posterior segments (table 2, figure 6). Ipsilateral phase relations are maintained at around 0.2 (figure 7) with strong coupling between exopodites separated by up to four segments (figure 8). Contralateral phase coupling within segments is also strong, with a dominant antiphase relation (figure 9). However, other stable coupling modes have also been observed (figure 10). The exopodite beat shows some phase interaction with another observed cyclical activity, the baling action of the epipodite on thoracic segment 1 (figure 11). These results are discussed in relation to the properties of other metachronal systems, and particular comparisons are drawn between the performance of exopodites in Praunus and in Homarus larvae (table 3). Possible mechanisms of neuronal coordination are considered.