You can find a good many of these creatures when you go to the seaside, by hunting about on the beach at low water. In some places on rocky coasts sea-urchins are very common. Sometimes they are known as sea-eggs, and in many countries they are actually boiled and eaten as food, just as we eat the eggs of fowls and ducks. And their shells are so thickly covered with spines that they look just like little hedgehogs which have rolled themselves up into balls.
When the animal is alive it can move these spines at will, each of them being fastened to the shell by a ball-and-socket joint, just like those which we described to you when we were telling about the vertebræ of the snakes. But after it has been dead for a few days they are nearly always knocked off by the action of the waves, so that the shell is left quite smooth and bare.
By means of these spines a sea-urchin can bury itself in the sand at the bottom of the sea in a very short time, only just a little funnel-shaped pit being left to show where it is hiding. And in some of the larger kinds they are really formidable weapons, for they grow to a length of eight or ten inches, and are so sharp and strong that they can actually pierce the sole of a stout shoe. Besides this, they have poison-glands connected with them, so that they can easily inflict a really serious wound.
In the shell of a sea-urchin are a number of little holes, through which the animal pokes out most curious sucker-like feet when it wants to climb about over the rocks. By means of the suckers on the upper part of the shell it often clings to small stones, which it sometimes gathers up in such numbers as to conceal itself entirely from sight.
Just inside the mouth of the urchin are five very large chisel-like teeth. These are formed just like the front teeth of the rodent animals, and grow as fast as they are worn away.
Sea-urchins are not numerous on the Atlantic shores of North America, because these shores are not rocky except in the cold north. One small flat kind, however, occurs in the deep waters off this coast, and its cases are often cast up on the beaches and are called sand-dollars. On the Pacific coast, however, sea-urchins are common and well known; and the Indians of the northwest coast boil them and eat them greedily.
Starfishes
More plentiful on both coasts, and extremely numerous and harmful in all the bays and sounds from Florida to Maine, are the starfishes, or fivefingers, as the oystermen call them. But although they are so abundant, very few people seem to know what curious creatures they are.
The starfish has hundreds of little sucker-like feet, just like those of the sea-urchin. You cannot see these, as a rule, because the starfish keeps them tucked away inside its skin. But when it wants to use them it can poke them out in a moment.
If you want to look at these odd little feet, the best way to do so is to take a live starfish, put it at the bottom of a pool of sea-water, and then wait patiently for ten minutes or a quarter of an hour. By the end of that time you are almost sure to see that the animal is slowly moving. Then snatch it out of the water, turn it upside down, and you will see hundreds of little white objects waving about on the lower surface of its body. These are its feet, and if you look at them through a good strong magnifying-glass, you will see that they are shaped just like wine-glasses, each having a kind of fleshy cup at the end of a slender stem. And at the end of the cup is the sucker.