The circulatory system of Penaeus vannamei Boone, 1931-Lacunar function and a reconsideration of the "open vs. closed system" debate.

The morphology of hemolymph circulatory systems has been studied in many arthropod groups over the past decades. In most cases, however, the focus of these studies has been the vascular system, while its counterpart, the lacunar system, has often been neglected. To further understanding of the interrelationships between these two complementary subsystems, we investigated both, the hemolymph vascular system and the hemolymph lacunar system, of the decapod Penaeus vannamei using 3D-imaging techniques (micro-computed tomography and confocal laser scanning microscopy) in combination with 3D reconstruction. Major parts of the vascular and lacunar system are described. Our insights into their morphology are used to derive functional conclusions for a model illustrating the interrelationships between the two subsystems. The morphology of and the functional interaction between the vascular and lacunar systems are discussed in the context of the debate on "open vs. closed circulatory systems."