A Review of the “Open” and “Closed” Circulatory Systems: New Terminology for Complex Invertebrate Circulatory Systems in Light of Current Findings
Figure 1
Schematics of:
(a) a classically defined “open” circulatory system (as seen in may lower
invertebrates), (b) a circulatory system that is highly complex with
capillary like vessels, a partially lined vasculature yet contains vascular
sinuses which classically has been defined as “open” yet should be categorized
as an “incompletely closed” circulatory system. (c) A classically defined
“closed” circulatory system (as seen in mammals and other higher vertebrates) ((c)
adapted from Whithers [1]). (Solid
lines represent defined vessels or a muscular pump or heart. Dashed lines
represent sinus based systems and/or vessels lacking a defined lining. Arrows
represent general patterns of blood flow. Background color is a general
indicator of arterial versus venous hemolymph or blood).
