Right anterior bundle (1) of pedal retractor muscle (PRM). Colourless haemolymph depleted of oxygen (white ‘V’s) leaves foot-head through gaps (2) between bundles of the PRM and enters afferent branchial vessel (3) along the sides of the PRM. Thence it passes through pallial gills (4) to receives oxygen and turn blue (blue ‘V’s) before passing into efferent branchial vessel (5) encircling the animal. Blue haemolymph passes from efferent vessel via large trunk (6) into heart in nuchal cavity (7) near left anterior muscle bundle. Heart pumps the oxygenated haemolymph to the organs of the foot-head. Colourless haemolymph depleted of oxygen again leaves foot-head via gaps between the bundles of PRM. Black mantle roof of nuchal cavity (8). Anterior attachment of mantle to shell (9). Sole (10). Left: L. 34 mm, Anglesey, March 2014. Right: L. 41.6 mm Mersey Estuary, August  2017.