Mapping the whole-body muscle activity of Hydra vulgaris

As a cnidarian, Hydra has an anatomically simple neuromuscular system that can offer evolutionary insights on the functional design of animal body plans. Using calcium imaging to map the activity of the entire epitheliomuscular system of behaving Hydra, we find seven basic spatiotemporal patterns of muscle activity. Patterns include global and local activation events with widely varying kinetics of initiation and wave-like propagation. The orthogonally oriented endodermal and ectodermal muscle fibers are jointly activated during longitudinal contraction. Individual epitheliomuscular cells do not have dedicated roles in muscle activity but participate in multiple patterns, even with very different kinetics. This multifunctionality of epitheliomuscular cells in basal metazoans could enable a structurally simple tissue to implement a varied behavior output.