Circulatory System
Malacostracans have a more complex open circulatory system than do other crustaceans. The single-chambered heart is enclosed in a pericardial sinus and is located dorsally, above the gut. It is elongate and tubular with several holes (ostia) for return flow in primitive forms (orders Leptostraca and Stomatopoda and the superorder Syncarida), but it is short and boxlike with one to two ostia and located in the thorax in advanced forms (decapods). The blood, or hemolymph, is pumped to the head through an aorta and to the gills and locomotor appendages through lateral and ventral arteries. Veins are lacking, and the blood returns to the heart via a series of sinuses.