Ra. Merz et Dr. Edwards, JOINTED SETAE - THEIR ROLE IN LOCOMOTION AND GAIT TRANSITIONS IN POLYCHAETE WORMS, Journal of experimental marine biology and ecology, 228(2), 1998, pp. 273-290
Many families of polychaete worms have jointed setae in which the join
t is external to the body and is not directly controlled by muscles or
nerves. We assessed the role of these specialized structures in the h
esionid polychaete, Ophiodromus pugettensis, by examining speed, step
length, stride distance, stride frequency and gait transitions in worm
s with and without setal joints. Individual worms were videotaped whil
e they moved over sandy surfaces at a range of speeds. The worms were
then anaesthetized and all their compound setae were trimmed either di
stally or proximally to the setal joints. After two days of recovery t
he worms were videotaped a second time while they again moved over san
dy surfaces at a range of speeds. From the video tapes we analyzed the
ir locomotory performance before and after setal ablation. Animals in
which the setae were shortened but in which the joint was left intact
showed no consistent change in speed, step length, stride distance, st
ride frequency or gait transitions. Animals in which the joint had bee
n removed both changed gaits at slower speeds (walking to undulatory w
alking and undulatory walking to swimming) and showed a significant de
crease in maximum swimming speeds and stride distance. A subset of dat
a containing only cases where the worms were moving at the same speed
in the same gait before and after setal ablation was analyzed. In thes
e instances, after the removal of the joint, the worms had significant
ly smaller stride distances and compensated for this by increasing str
ide frequency. In O. pugettensis, the undulatory walking gait is analo
gous to the trot-gallop transition in quadrupedal mammals because the
animal switches from moving the appendages on a relatively rigid body
to using a combination of body flexion and appendage movement to achie
ve propulsion, however, unlike quadrupedal mammals this transition tak
es place over a wide range of speeds and at different sites on the bod
y as speed increases. These experiments indicate that jointed setae ma
y be important both in allowing a worm to better control setal contact
and traction with the substrate as well as in altering the effectiven
ess of its swimming stroke. (C) 1998 Elsevier Science B.V. All rights
reserved.