Blog 13 Compare the circulation of a segmented worm a starfish and a grasshopper

Grasshoppers have open circulatory systems, with most of the body fluid filling body cavities and appendages. The one closed organ, the dorsal vessel, extends from the head through the thorax to the hind end. It is a continuous tube with two regions: the heart, which is restricted to the abdomen; and the aorta, which extends from the heart to the head through the thorax. Haemolymph is pumped forward from the hind end and the sides of the body through a series of valved chambers, each of which contains a pair of lateral openings. The haemolymph continues to the aorta and is discharged through the front of the head. Accessory pumps carry haemolymph through the wing veins and along the legs and antennae before it flows back to the abdomen. This haemolymph circulates nutrients through the body and carries metabolic wastes to the malphighian tubes to be excreted. Because it does not carry oxygen, grasshopper blood is green.

The starfish has radial canals that go through all the legs and join in the center to make the water vascular

system that functions as a circulatory system, waste removal and more.

Starfish are almost unique in the fact that, unlike most other animals, they do not have blood but instead use sea water to pump around their bodies. The water vascular system uses cilia and the constantly contracting ampullae to keep things moving. An ionic imbalance causes water to flow into the madreporite, entering the water vascular system. Some of this water is diverted into the periviscerial coelom (the large cavity in which major organs are suspended), where it is circulated by the beating of cilia. Most oxygen enters the starfish via diffusion into the tube feet (with the water vascular system), or the papulae (small sacs covering the upper body surface.There are about 1,800 living species of sea star, and they occur in all of the Earth's oceans. The greatest variety of sea stars are found in the northern Pacific Ocean.

Circulation in a segmented worm is through a series of closed vessels. The two main vessels that can be seen in your dissection are the dorsal and ventral blood vessels. These vessels are the main pumping structures. In the dorsal vessel, blood moves anteriorly. The dorsal vessel is the dark line running along the dorsal surface of the digestive tract. In the posterior third of your worm, carefully cut through and remove about three centimeters of the digestive tract. The ventral blood vessel can usually be seen adhering to the segment of intestine removed. In the ventral vessel, blood moves posteriorly. Segmental branches off the ventral vessel supply the intestine and body wall with blood. These branches eventually break into capillary beds to pick up or release nutrients and, oxygen. Gas exchange occurs between the capillary beds of the body surface and the environment. Oxygen is carried by the respiratory pigment hemoglobin, which is dissolved in the fluid portion of the blood. From these capillary beds, blood is collected into larger vessels that eventually unite with the dorsal vessel. At the level of the esophagus, segmental branches are expanded into five pairs of aortic arches, or what have been called "hearts". They are dark, expanded structures on either side of the esophagus. Although these are contractile, they only function in pumping blood from the dorsal to the ventral vessels.