BODY FLUIDS AND CIRCULATION 



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ctenidia, from which efferent vessels return blood to the auricles. Many of 

 the veins are also contractile, showing peristaltic movements, and venous 

 valves occur which regulate the direction of flow. 



Rate of heart beat is generally slow in lamellibranchs and gastropods, 

 around 10-20 beats per min, and higher in cephalopods, up to 80 beats per 



TABLE 3.3 

 Representative Figures for Heart Frequencies 



min (Table 3.3). Cephalopods are active animals with high respiratory 

 rates, and have need of an efficient circulatory system. Blood pressures are 

 high, due in part to rapid heart beat, and in part to the closed circulation 

 and strength of the cardiac pump; the circulatory volume is certainly 

 small (unknown, but only some fraction of total extracellular fluid). In 



