Neuronal control of swimming in jellyfish: a comparative story

The swim-control systems of hydrozoan and scyphozoan medusae show distinct differences despite similarity in the mechanics of swimming in the two groups. This dichotomy was first demonstrated by G.J. Romanes at the end of the 19th century, yet his results still accurately highlight differences in the neuronal control systems in the two groups. A review of current information on swim-control systems reveals an elaboration of Romanes' dichotomy, but no significant changes to it. The dichotomy is used to suggest that cubomedusae are more closely aligned with the scyphomedusae, and to highlight areas of future research that could be used to look for common, possibly primitive, features of medusan conduction systems.