Sea Star Pre-Lab Activity

Kindom – Animalia Phylum – Echnidermata Class (see next slide please)

Sea Star Classes Similarities aside, the differences between them have led to the division of the phylum into five living classes.  So, while they are all cousins, we can call various sorts of them either Asteroids, Ophiuroids, Crinoids, Echinoids, or Holothuroids.                              

Catching and Holding Their Food Echinoderms also share a unique body system called the water-vascular system, which no other group of animals possess. This is a complex system of muscles, canals, pouches, bladders, tubes, and suckers that allow Echinoderms to move around and to eat.

Catching and Holding Their Food (cont.) You can't see it on the inside of an Echinoderm without opening it, of course, but if you take an up close look at any Sea Star , you’ll immediately see that they have lots and lots of suction cup-tipped “tube feet” that emerge from the grooves on their undersides. Through coordinated movement of these tube feet, the owner can move about surprisingly quickly.

Catching and Holding Their Food (cont.) They can also grab hold of a seemingly impenetrable clam and open its shell wide enough to make a meal of it, or climb right up the side of your aquarium. Likewise, other Echinoderms use their tube-feet, or similar extensions of the water-vascular system to capture planktonic foods, or to burrow through substrates, etc. Again, it doesn't matter what they look like, they all have a W. V. S.

Greek Echinoderms mean "spiny skin" in Greek. Many, but not all, echinoderms have spiny skin.

Water Vascular System Sea stars and their relatives, called echinoderms, have a unique method of movement called a water vascular system. This is a network of “plumbing” running through the body designed to bring water to and from the tube feet. Water enters the water vascular system through the sieve plate (also called the madreporite) on the top surface of the body. On this sea star it is an orange or red spot on the top surface, often mistaken for an eye.

Water Vascular System (cont.) Water entering the sieve plate goes into a structure called a stone canal which carries the water into the interior. Here the water is collected in a water ring which encircles the main body. Branching from the water ring, into each arm, is another “pipe” called a radial canal. Water in the radial canals finally reach the tube feet, where it is used to control the stretching of the feet and the suction cup on the ends.

Water Vascular System (cont.) The tube feet, known as ambulacrae, are set into a groove on the underside of the arm called an ambulacral groove. To move, the starfish fills the foot with water, stretching the foot out. When the suction cup touches the surface of an object the center of the cup is raised slightly creating a vacuum and causing the foot to stick. Pushing the center of the cup back out (using water pressure from the tube foot) “pops” the suction cup off the surface again.

Don’t forget to clean your dissecting instruments and tray when finished, please! Let’s Dissect!!! : )