Scyphozoan jellyfish are free-swimming gelatinous organisms whose nervous system
includes a motor nerve net that controls swimming. Swim contractions originate in a network of
distributed pacemakers found in the marginal rhopalia, which are located around the margin of
the bell. Many scyphozoan jellyfish have eight rhopalia, while others have sixteen or more. At
any one time, the fastest pacemaker controls the output of the swim system. The activity of a
single pacemaker is irregular; however, by linking multiple irregular pacemakers the swim
system exhibits regular contractions. Thus, multiple pacemakers are believed to increase the
frequency and regularity of swim contractions. Pacemaker interactions in Chrysaora
quinquecirrha, Stomolophus meleagris, Aurelia aurita, and the ephyra of Aurelia aurita were
investigated using artificial pacemaker networks created from pacemaker ablation experiments.
In all species, with increasing pacemaker number, the frequency and regularity of swimming
increased. Integrate and fire pacemaker models were used to determine if the pacemaker
networks of three species of scyphomedusae were resetting, independent, or semi-independent.
It is concluded that Chrysaora quinquecirrha and Stomolophus meleagris have a resetting
pacemaker networks. In contrast, Aurelia aurita has a semi-independent pacemaker network and
the ephyra of Aurelia aurita has resetting pacemaker network
