Muscle organization of the cubozoan jellyfish Tripedalia cystophora Conant 1897.

The musculature of the cubomedusa Tripedalia cystophora was investigated using immunohistochemical staining with an anti-actin antibody and histochemical staining with fluorescent phalloidin. The subumbrella is lined with a sheet of circular, striated muscle that is interrupted at the perradii, and by the nerve ring. The sheet is continuous with circular, striated muscle of the velarium, which turns radially on each face of the four velarial frenula. Perradial strips of smooth muscle run radially from just above the level of the rhopalia into the manubrium and lips. The strips give off perpendicular offshoots that run a short distance in parallel with the circular swim muscle. Musculature of the tentacles and pedalia is longitudinal and limited to the oral side of the pedalia. The pedalial muscle connects with bundles of smooth muscle that runs circularly from the tentacle base well into the subumbrella. The arrangement of striated muscle in the frenula suggests that these structures may function in directional nozzle formation of the velarium during turning. In addition, the perpendicular branching of the radial strips and the circular extensions of pedalial muscle may function in hinge formation to aid bending of the pedalia and tentacles into the subumbrella during feeding and protective responses.