Figure 8

The bidirectional crawling and motion model. (a) The fins and girdle muscles. (b,c) Forward and backward crawling, red lines mean abducted fin, blue lines mean adducted fin, red line with arrows means protractor ischia, and blue line with arrows means retractor ischia.(d,g) Forward and backward crawling model. (e,h) Force analysis during forward and backward crawling. (f,i) Forward and backward mode of swing car. Purple lines trace the movement of the anterior-most point on the head; the black dashed lines trace the movements of the rotating fins; the solid blue lines trace the movements of the resting fins; the thick blue thick lines show the spine, which constrained the relative motions of the pectoral and pelvic suckers. The spine model was a bending bar of almost constant length. The figure is drawn by Jinrong Wang.