Anatomy of finfish and shellfish

Unit 12 - Arthropoda

12.2.3.Circulatory System
The circulatory system of a lobster is not very different from that of the white shrimp. In lobsters as in shrimps, the heart lies under the middorsal surface of the cephalothorax just in front of its junction with the abdomen. Three pairs of ostia allow blood that has collected within the pericardium to flow into the heart when the organ relaxes. During contraction of the heart, the ostia close and prevent the blood from flowing back into the pericardium.
From the heart;-the blood flows forward through several arteries to vital organs within the cephalothorax. The blood also flows into the dorsal abdominal artery and its paired branches in each segment. These supply blood to the ven¬trally situated flexor muscles and the dosal1y situated exten¬sor muscles of the abdomen. A sternal artery carries blood to the gonads, then courses ventrally to give rise to the ventral thoracic artery and the ventral abdominal artery. In lobsters, as in shrimps, the ventral thoracic artery carries blood to most thoracic appendages and to the thoracic portion of the ventral nerve cord. In lobsters, but not in shrimps, the ventral abdom¬inal artery extends through the abdomen, supplying blood to the last two pairs of thoracic legs, the ventral nerve cord, the posterior part of the hind gut, and the tail fan.