what is oragan system organization . and what are haemocoelomates?

Organ system organisation refers to a group of interacting, interrelated, or interdependent organs working together to perform a certain task. Example :circulatory system, respiratory system, nervous system 

 

 

A hemocoel (also spelled Haemocoel) is a series of spaces between the organs of organisms with open circulatory systems, like most arthropods and molluscs. A combination of blood, lymph, and interstitial fluid called hemolymph circulates through the hemocoel.