It was pretty certain we should find a starfish down near low-water mark, and here is a fine one.
Starfishes are among the oddest of sea-animals; for one reason, because they have so many legs. Perhaps you did not know they had any legs at all; certainly you can see none when you pick up a dead specimen on the beach. The fact is that a starfish keeps its legs inside its body, where there are a lot of organs protected by its hard, limy hide; and when it wants to use them it pokes them out through little holes on its under or grooved side, and fills them with water.
You would like to see its legs, no doubt. Very well; you shall. This starfish is still alive: we can easily see that, for when we pick it up its rays stand stiffly out; but if it were dead they would be quite soft and flabby, and would hang down. So we will put it into a shallow pool of clear sea-water, and see what happens. There! did you notice that it moved one of its rays? See, the one in front is being slowly pushed forward. Now the rays behind are being drawn up; and now that they have taken a fresh hold the front one is being pushed forward again. The starfish is really walking! What will it do when it comes to a stone? Why, walk over it! What will it do when it comes to rock? Why, climb up it! Now take the starfish out of the water. Turn it over on its back. There! do you see? On the lower surface of every ray are hundreds of little fleshy objects waving about in the air. Those are its "feet," or at least its means of walking; and each has a sort of cup at the end which acts as a sucker. By means of these the starfish can cling tightly to the surface of a stone. So by using first the little sucker-legs on one or two of its rays, and then those on the others, the starfish is able to crawl about quite easily.
The starfishes live upon animal food—mainly other mollusks, which they kill in a very curious manner. When, in crawling about, they come upon a whelk or clam or oyster, they creep over it and clasp it in their five arms in a murderous embrace from which there is no escape. Even if the creature can move off, its captor clings to it with its hundreds of tiny suckers, and rides along with it like that Old Man of the Sea in Sindbad's story.
Now if you look again at our specimen you will see on its under side, a small pit in the center of its body, closed by five points. This is the mouth, and the points are sharp. As soon as the starfish has a grip upon its victim the mouth opens and there is gradually pushed out a strong membrane which is the creature's great loose stomach. This envelops the animal, shell and all, or as much of it as possible, and soon begins actually to digest the flesh. When the meal is finished the starfish draws back its stomach and leaves only the empty shell of its prey.
These voracious starfish are a worse enemy to the cultivated oysters than are the drills; and, having an abundance of food on the thickly planted beds, they become extremely numerous, so that it costs the owners of the beds much money each year to gather them off the beds by means of a sort of great rake called the tangles. Otherwise the oysters would soon be wholly destroyed. The men used simply to tear to pieces what they caught and throw them overboard again; but they soon learned that this was worse than useless, because each half, or even a single arm, would not only go on living but would reproduce all the missing parts; so that in trying to kill one starfish they had brought to life two or perhaps even five, which was very discouraging. Nowadays, therefore, all captured starfishes are brought ashore and left there, and often are made use of by being ground up with oyster-shells, fish-bones, etc., into an excellent fertilizer.
What is that greenish-gray object covered all over with spikes? It is clinging in a little hollow of the rock, half hidden in seaweed of the same color.
Ah! that is a sea-urchin, and although it looks so very unlike them it is really a kind of first cousin to the starfishes. Here is a dead one from which the spines have been knocked off. Just look at it carefully, and you will see that it is very much like a starfish rolled up into a ball. See, you can trace the five rays quite easily, and if you look at it through a strong magnifying-glass you will find that its surface is pierced in hundreds of places with tiny holes through which it can poke out little sucker-feet, just as the starfishes do.
Look again at the shell from which the spines have been knocked away. Do you see that it is covered all over with little pimples? Now on every one of these pimples a spine was fastened by a kind of ball-and-socket joint, the pimple being the ball, and the socket lying inside the base of the spine; and by means of special muscles the animal could move the spines about, just as though it were a kind of hedgehog. In fact, this is the reason why it is called sea-urchin, for urchin is an old name for hedgehog. So, when a sea-urchin crawls about, it does so partly with its sucker-feet, and partly with its spines as well.
Sometimes, however, these creatures use their sucker-feet for quite a different purpose. They poke them out as far as they can from among their spines, and then take hold of little stones, small pieces of broken shell, and other bits of rubbish which they find at the bottom of the sea, and cling to them very tightly. The consequence is that you cannot see the animal at all, for it is quite concealed by this curious covering, and unless you were to take it out of the water, you would never have the least idea what it really was.