Physiology of Finfish and Shellfish

2.2.26. Circulation -Hemalymph flow

In crustaceans, hemolymph flows from the heart to the body, then to the gills and back to the heart. The beating heart may be seen by flexing the abdomen downward and looking beneath the dorsal carapace of the cephalothorax. Contraction of the heart pumps hemolymph through seven arteries include the ophthalmic (cephalic, median, anterior aorta), the paired antennal, and the paired hepatic arteries.

The major arteries branch to varying degrees to form vessels with increasingly small diameter. The smallest vessels often with lumen diameters of less than 8 mm, have been called capillaries. We propose that they be called arterioles, because they appear to be important in the distribution of hemolymph rather than the exchange of metabolites between hemolymph and tissues. Deoxygenated hemolymph from the sinuses and the capillaries eventually merges in the sterna sinus. Hemolymph then enters the offerent branchial sinuses of the gills. Then it flows through all over the body.