Cord muscle is present in polyps and strobilae of C. quinquecirrha but absent in P. noctiluca. Figures are oriented oral end down with lateral views unless otherwise noted. Muscle structures are stained with BODIPY Phallacidin (A, B, C, E, G) or alexa-fluor phalloidin (D, H), and generated on a confocal microscope, except (D), which was imaged on a multiphoton microscope. (A) A Chrysaora quinquecirrha polyp newly emerged from a podocyst, showing three visible polyp cord muscles (pcm) extending from the foot (ft) to the oral disk (od). (B) Large polyp showing six cord muscles (pcm) running from the foot (ft) to the oral disk (od). (C) Polyp cord muscles (pcm) in strobilae are centrally located and appear as stripes running along the oral-aboral axis. Aborally, these cord muscles are thick and well formed, growing thin orally as ephyrae mature and degrading completely after ephyrae detach. (D) Oral view of a developing ephyra cut from a strobila, showing three of the four polyp cord muscles (pcm) around the immature ephyra mouth, developing ephyra muscle (em) around the margin near the rhopalial lappets (rl) and rhopalia (r), and oral myoepithelia (ome) bundles radiating from the corners of the mouth. (E)
Pelagia noctiluca at the four-prong stage showing no evidence of cord-like muscle on the oral-aboral axis. (F) Diagram of the same four-prong stage showing the endoderm (end, blue) and ectoderm (ect, green). (G) Oblique view of a P. noctiluca cone larva (compressed laterally) with small arm buds forming, and actin-rich bundles of developing ephyra muscle (em) around the circumference of the future mouth. No cord-like muscles are present. (H) An oral view of a more mature P. noctiluca showing no evidence of cord-like muscle around the mouth but with developing rhopalia. * = Mouth. All scale bars are 100 μm.