Figure 1. An abbreviated phylogeny of the Nudipleura Clade within Opisthobranchia.

The Nudipleura clade consists of the monophyletic clades Nudibranchia and Pleurobranchomorpha. Within Nudibranchia is the clade Cladobranchia, which consists of Dendronotida and Aeolida. Nudibranchia also includes the clade Doridoidea. The genera studied here are in bold. Genera in green boxes are genera that include species that produce rhythmic, dorsal-ventral flexions, in turquoise boxes are genera that produce rhythmic, left-right flexions, and in red boxes have not been observed to produce rhythmic body flexions. Larger boxes indicate monophyletic clades.