The open circulatory system is a type of circulatory system in which nutrients and wastes move freely in the body cavity and not blood vessels. This type of circulatory system is found in insects, molluscs etc. In the case of cockroach, the open circulatory system is not of a physiological hindrance as circulatory and respiratory systems are not connected. Respiration mainly takes place by special respiratory organs known as spiracles.
Hence, the correct answer is option “C”- Circulatory and respiratory system are not connected.