In this Radiate, the disk spreads out, so as to include, or shut in, the rays. On the one hand, there are some star-fish that have the disk very small. They seem to be all rays and no disk.
People who have studied star-fish divide them into six families. I have told you about all but the fifth. The fifth family are of such a queer shape that they are called cucumbers—Sea-Cucumbers. The Chinese like to eat them, and ships are sent out to fish for them. They grow in the shallows, near the islands in tropic seas. We have some also on our coasts.
LESSON XL.
THE STAR-FISH WITH AN OVERCOAT.
There is a very pretty star-fish called the Sea-Egg, or Sea-Urchin. This creature has not five points or rays; it is in the shape of a ball, somewhat flattened.
Fig. 1. Fig. 2. Fig. 3.
Do you say, “Can this belong to the Star-fish Family, when it has no rays?” Well, let us see. Let Figure 1 represent our Ray pattern. Bend the rays up, and the plan looks like Figure 2. Then bend them until the tips touch, and you have the form of Figure 3. The cover of this star-fish, called the sea-urchin, is not tough and skin-like; it is hard and shell-like.
If you look at it, you will see that it has up and down it lines of knobs and dots set in double rows. You will find five double lines of large knobs, and as many lines of small dots between the larger ones.
Do not think that you can see these marks as soon as you find a sea-urchin. By no means! The sea-urchin wears a fine thick overcoat, which hides his shell.