On your laboratory test, you are presented with a mollusc that has a closed circulatory system. You know immediately that it must belong to the class .

Cephalopoda

Explanation:

Cephalopods are the mollusk that has a closed circulatory system by simple circulation. The heart is located in the pericardic cavity and it is divided into two auricles and one ventricle. From the ventricle, the anterior aorta goes forward the head and the posterior aorta goes forward the visceral mass. The anterior aorta branches into many branchial arteries. All of them get united again in the head, in one cava vein from where the blood returns to the posterior extreme. This vein introduces into the pericardic cavity and brunches into two renal veins near the nephridium. Each branch penetrates into a nephridial sac and passes through the muscular branchial heart before it enters the gills.  Blood passes from the ventricle to the branchia through many vessels. In the branchia, the blood gets oxygenated again and returns to the auricle. The posterior aorta irrigates the gonads and the mantle, and from the posterior extreme of the body, blood goes forward to the anterior body region through two veins that join the renal veins that flow into gill hearts.      

a covalent bond, specfically triple bond