25. In which of the following animals, is open circulatory system found?

(A) Prawn

(B) Earthworm

(C) Toad

(D) Man

Ans. (A) Prawn

The open circulatory system is a system in which fluid in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients and there is no distinction between blood and interstitial fluid. 

Prawns, like all crustaceans and most invertebrates, have an open circulatory system.