The Contribution of the Branchial Heart to the Accessory Branchial Pump in the Octopoda

The octopus circulatory system is atypical of the molluscs, with a medially situated ventricle generating high arterial blood pressures (Johansen & Martin, 1962; Wells, 1979). Using free-moving Octopus dofleini, Johansen & Martin (1962) demonstrated the presence of an accessory branchial pump, boosting the venous blood pressure, between the anterior vena cava and the afferent branchial vessel. Traditionally it has been assumed that the branchial hearts are responsible for this increase in the venous pressure, although there is no direct physiological evidence to support this idea. Within the published literature, however, there are several observations which indicate an additional source of pressure generation. The present paper draws these observations together and re-examines the possible locations of the accessory branchial pump.