Close/open shells (Fig. 3-II). Transverse T1w-MRI of a close/open process of the shells of Mytilus galloprovincialis. Images are presented by 2.56 times speed from 215 sec to 256 sec (128 images every 0.32 sec). Slice position is set at the AV valve. A change in area of the water flow during the first open/close process in the mantle cavity is shown in Fig. 3-II.