Anatomy of finfish and shellfish

Unit 13 - Mollusca

13.3.6. Blood Vascular System
The circulatory system is well formed and of the closed type. It is unique in that it has two types of hearts. At the base of each gill is a rounded organ, the branchial heart. They receive venous blood of the body through larger veins or venae cavac. Each gill heart pumps blood to the gill of its side. The oxyge¬nated blood from the gills is collected in an auricle on each side. The two auricles join the single ventricle of the systemic heart, which sends arterial blood to all parts of the body by three aortae. In the tissues the arterial capillaries join the venous capillaries, which finally form the larger veins leading to the branchial hearts.