Mollusks have a circulatory system with one or two hearts that pump blood, and arthropods and most mollusks have an open circulatory system. Given these facts, what kind of circulatory system do arthropods have among the following options:
- open
 - toads
 - closed
 - porous
 - fluid
 - H 2 O
 - tissue
 - koalas


 

 open        