Jellyfish Locomotion

Two dichotomies exist within the swim systems of jellyfish—one centered on the mechanics of locomotion and the other on phylogenetic differences in nervous system organization. For example, medusae with prolate body forms use a jet propulsion mechanism, whereas medusae with oblate body forms use a drag-based marginal rowing mechanism. Independent of this dichotomy, the nervous systems of hydromedusae are very different from those of scyphomedusae and cubomedusae. In hydromedusae, marginal nerve rings contain parallel networks of neurons that include the pacemaker network for the control of swim contractions. Sensory structures are similarly distributed around the margin. In scyphomedusae and cubomedusae, the swim pacemakers are restricted to marginal integration centers called rhopalia. These ganglionlike structures house specialized sensory organs. The swim system adaptations of these three classes (Hydrozoa, Scyphozoa, and Cubozoa), which are constrained by phylogenetics, still adhere to the biomechanical efficiencies of the prolate/oblate dichotomy. This speaks to the adaptational abilities of the cnidarian nervous system as specialized in the medusoid forms.