Internal Anatomy
As echinoderms, starfish possess a hydraulic water vascular system that aids in locomotion. This system has many projections called tube feet on the starfish's arms which function in locomotion and aid with feeding. Tube feet emerge through openings in the endoskeleton and are externally expressed through the open grooves present along the oral surface of each arm.
The body cavity also contains the circulatory system, called the hemal system. Hemal channels form rings around the mouth (the oral hemal ring), nearer to the aboral surface and around the digestive system (the gastric hemal ring). A portion of the body cavity called the axial sinus connects the three rings. Each arm also has hemal channels running next to the gonads. These channels have blind ends and there is no continuous circulation of the blood.
On the end of each arm is a tiny simple eye which allows the starfish to perceive the difference between light and darkness. This is useful in the detection of moving objects. Only part of each cell is pigmented (thus a red or black colour) and there is no cornea or iris. This eye is known as a pigment spot ocellus.
Read more about this topic: Starfish
Famous quotes containing the words internal and/or anatomy:
“I believe that there was a great age, a great epoch when man did not make war: previous to 2000 B.C. Then the self had not really become aware of itself, it had not separated itself off, the spirit was not yet born, so there was no internal conflict, and hence no permanent external conflict.”
—D.H. (David Herbert)
“But a man must keep an eye on his servants, if he would not have them rule him. Man is a shrewd inventor, and is ever taking the hint of a new machine from his own structure, adapting some secret of his own anatomy in iron, wood, and leather, to some required function in the work of the world. But it is found that the machine unmans the user. What he gains in making cloth, he loses in general power.”
—Ralph Waldo Emerson (1803–1882)