Concept
Version 9
Created by Boundless
Open and Closed Circulatory Systems
Closed and open circulatory systems
(a) In closed circulatory systems, the heart pumps blood through vessels that are separate from the interstitial fluid of the body. Most vertebrates and some invertebrates, such as this annelid earthworm, have a closed circulatory system. (b) In open circulatory systems, a fluid called hemolymph is pumped through a blood vessel that empties into the body cavity. Hemolymph returns to the blood vessel through openings called ostia. Arthropods, such as this bee and most mollusks, have open circulatory systems.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"OpenStax College, Overview of the Circulatory System. October 17, 2013."
http://cnx.org/content/m44801/latest/Figure_40_01_01ab.jpg
OpenStax CNX
CC BY 3.0.