Fig. 3.
Siphon, body wall, and cardiac muscles of adult ascidians. a Diagram of an adult Ciona intestinalis, showing the muscle fibers of oral siphon (OS), atrial siphon (AS), and body wall muscles. Illustration adapted from Berrill [25]. b Juvenile Molgula occidentalis, stained with Phalloidin-Alexa Fluor 488 to visualize developing myofibril bundles. Hollow arrowhead: oral siphon muscle rings. Hollow double arrowhead, oral siphon-derived latitudinal body wall muscles; solid arrowhead, atrial siphon muscles; solid double arrowhead, atrial siphon-derived longitudinal body wall muscles; OS, oral siphon; AS, atrial siphon. c Diagram of the heart of an adult Ciona intestinalis. Arrows indicate blood flow in one direction, although ascidian hearts will periodically reverse their beat and pump blood in the opposite direction. Eso, esophagus; en, endoderm; st, stomach.