The function of parapodial setae in a nereidid polychaete moving on two different substrata

Active polychaetes of the family Nereididae possess a large number of compound setae originating in seta-bundles at the distal end of the parapodium. Here we investigate the functional role of the setae in Nereis diversicolor by comparing the locomotor performance of neuropodial seta-ablated worms with normal (control, non-ablated) worms moving on sand and mud. No differences between worms walking on sand and mud were found, except that they were more submerged in the latter substratum. On both substrata, a similar decrease in forward speed and increase in wave speed and slip were found in seta-ablated worms. However, this was not associated with any changes in gait, since both amplitude and wavelength were similar for seta-ablated and control worms. This suggests that the setae are not adapted to a specific habitat. The same parameters were compared between seta-ablated and control worms swimming over the substratum, but no significant differences were found, indicating that the setae are not as important during swimming as previously thought.