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Closed Circulatory System (Mammalian)
Mammalian hearts are a part of a closed circulatory system. This means the blood is closed within vessels throughout the body at all times and is pumped for circulation and oxygenation. In this system, blood is pumped through vessels, such as ventricles, veins and arteries, throughout the entire body by the force of the heart. The blood never travels to areas of the body that have no blood vessels.
Open Circulatory System (Crustacean)
The open circulatory system, characteristic of crustaceans, differs greatly from the closed system present in mammals. This system pumps blood to the cavities of the body, surrounding tissues and organs with nutrient- and oxygen-rich blood. When the heart relaxes, it fills with blood through the ostia, large pores that open when the heart is in a relaxed state. Within the heart, the blood is oxygenated and then pumped out to refill the crustacean's inner cavities.
Myogenic Heart (Mammalian)
Mammalian hearts are myogenic. This means that the heart contracts spontaneously. A myogenic heart does not require a command from the nervous system and contracts automatically. In other words, the contraction is initiated by the heart muscle itself without any electrical stimulation from the nerves.
Neurogenic Heart (Crustacean)
Unlike mammals, crustaceans have neurogenic hearts. A neurogenic heart requires stimulation from the nervous system to contract. For this to happen, the crustacean heart's external wall is coated with a cluster of neurons that produce a rhythmic output to generate the heartbeat. In other words, without nervous stimulation the heart would not contract.