FUNCTIONAL-MORPHOLOGY AND SIGNIFICANCE OF THE CIRCULATORY-SYSTEM OF OSTRACODA, EXEMPLIFIED BY VARGULA-HILGENDORFII (MYODOCOPIDA)

Combined high-resolution video-recordings of live specimens, SEM and s erial microtome sections were used to document the morphofunctional as pects of blood (hemolymph) circulation in Ostracoda, exemplified by th e nektobenthic myodocopid Vargula hilgendorfii from Japan. The circula tory system is comprised of a single-chambered dorsal heart (pericardi um, myocardium with two ostia), efferent vessels (aorta and secondary arteries) and an integumental afferent network of sinuses radiating fr om the adductor muscle area to a peripheral channel leading to heart. The heartbeat and the linear velocity of hemolymph in sinuses range fr om 0.5 to 6 times s(-1) and 200 to 1000 mu m s(-1), respectively. Hemo cytes (10 to 17 mu m) of irregular shapes occur within the circulating hemolymph. This typical open circulatory system is found in most myod ocope ostracodes and other crustaceans. It is totally absent in small( mostly < 2 mm) ostracodes such as Podocopa. We conclude that the fluid convection of hemolymph augments the diffusion process of Oz in large r animals. Oxygen uptake is assumed to occur preferentially through th e inner (posterior) surface of the carapace where hemolymph sinuses ar e best developed and in close contact with sea water. Hemocytes may be involved in coagulation processes as in other crustaceans (e.g. Decap oda). Integumental circulation, preserved as anastomosing features in fossil Ostracoda, is known from the early Palaeozoic through to the Re cent.