KING, A.J.*; ADAMO, S.A.; Dalhousie University, Halifax, Canada: Pulling for the greater good – elements of cuttlefish ventilatory and circulatory systems work together to circulate blood or to aid crypsis.

Cephalopod blood is ~ 30% more viscous than human blood, and their hearts make up only 0.1 to 0.3% of their body weight (vs. 0.6% in mammals). Regardless, they have high pressure, closed circulatory systems, similar to those of mammals. How do cephalopods compensate for elevated blood viscosity and low heart masses to achieve cardiac outputs that in some cases approach those of human athletes? Most large blood vessels in the cuttlefish, Sepia officinalis, are contractile. Using non-invasive ultrasound, we found that the vessels around the three hearts contracted in a coordinated way with them (61/63 observations, 8 animals). This coordination could reduce the work needed from the hearts to move blood from the venous return, through the gills, to the systemic arteries. Additionally, the hearts, main arteries, and main veins of cephalopods are enclosed in the muscular ventilating structure, the mantle. While contractions of the mantle were not synchronized with those of the heart (63/64 observations, 7 animals), they are almost simultaneous with the contractions of the main venous return vessel (25/25 observations, 6 animals). This synchrony could use the pressures created by the mantle during ventilation in two ways, first to help move the large volumes of blood in the venous return vessel; second to help increase the blood’s pressure as it returns to the systemic heart. When startled by sudden overhead movement, contractions of the mantle, as well as contractions of the systemic heart and main venous return vessel slowed (12/12 trials, 3-31 s) and stopped (6/12 trials, 3-10 s), while the animal simultaneously assumed a motionless, flattened posture. This complete immobility, both inside and superficially, may help cuttlefish avoid predation.