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No description available.

Recent molecular evidence suggests staurozoans are medusozoans that diverged from Medusozoa before the medusa stage emerged. Morphological studies are needed to determine whether this framework can provide insight into medusa evolution. I studied the neuromuscular morphology of two staurozoans, Haliclystus ‘sanjuanensis’ and Manania handi using FMRFamide and α-tubulin antibodies to label neurons, and phalloidin to label muscles. Results indicate that similar to polyps, staurozoans possess one regionally differentiated FMRFamide and α-tubulin immunoreactive (IR) nerve net, and smooth muscles only. Comparisons with other cnidarians indicate that ancestral medusozoans had a marginal circular muscle and muscular manubrium, but lacked the parallel conducting nerve nets, striated muscle, and pacemaker required to coordinate medusa swimming. A possibly light-sensitive concentration of neurons at the base of the primary tentacles suggests that staurozoan primary tentacles are homologous to medusozoan rhopalia. The unique neuromusculature of nematocyst clusters suggests a defensive or predatory function for these staurozoan synapomorphies. / Graduate / 0287 / 0317