Euopisthobranchs: Body Cavities

Abstract

Like in other mollusks, Euopisthobranchia possesses two different mesodermal body cavities that are discriminated by their lining. The pericardium is a secondary or coelomic body cavity, lined by an endothelium consisting of epithelio‐muscle cells, podocytes, and lining cells. The pericardium surrounds the heart that consists of a single auricle and the ventricle. Both are lined by an extracellular matrix only. The epicardium and myocardium are exclusively formed by the endothelium of the pericardium. A renopericaridal duct drains the pericardium and connects it to the kidney. The term renopericardial system expresses this structural relation. Since heart, aorta, arteries, veins, blood sinuses, and the large periintestinal hemocoel are lined by an extracellular matrix only, they form the primary body cavity of Euopisthobranchia. Since hemolymph flows inside this cavity and course and position only of parts of the primary body cavity are fixed, this cavity represents the semi‐open circulatory system of euopisthobranchs. The gonad may represent another secondary body cavity in Euopisthobranchia.