Wiktionary
open circulatory system
n. circulation which is achieved primarily from the heart beating and muscle-induced locomotion of the organism, circulation without veins
Usage examples of "open circulatory system".
The thranx organism was exceptionally tough, but very vulnerable to deep cuts and punctures because of their open circulatory system.
Blood and internal fluids gushed forth in a green fountain as the open circulatory system was ruptured.
A hundred-per cent insectoid, hard-shelled, open circulatory system, compound eyes, rigid, inflexible joints .