Types of intestinal loops in the genus Onchidium. Small black arrows indicate the direction of the intestinal transport, which starts in the blue loop. A blue loop turns clockwise. A yellow loop turns counterclockwise. A green loop is transitional in between a blue loop and a yellow loop. The orientation of the transitional (green) loop is indicated with a red arrow. Details on individuals of O. reevesii, O. typhae, O. stuxbergi can be found in Dayrat et al. (2016) A O. typhae, type II with a transitional loop at 9 o’clock, [1007] B O. typhae, type II with a transitional loop at 8 o’clock (from Dayrat et al. 2016: fig. 5E) C O. stuxbergi, type III with a transitional loop at 3 o’clock (from Dayrat et al. 2016: fig. 11B) D O. stuxbergi, type III with a transitional loop at 1 o’clock, (PNM 041200) E O. stuxbergi, type III with a transitional loop at 8 o’clock, [5605] F O. reevesii, holotype, type III with a transitional loop at 2 o’clock (from Dayrat et al. 2016: fig. 14A) G O. melakense, type III with a transitional loop at 1 o’clock, holotype [5979] (USMMC 00075) H O. melakense, type III with a transitional loop at 5 o’clock, [5978] (USMMC 00076). Scale bars: 3 mm (A, H), 5 mm (B, C, E–G), 4 mm (D).