The Animal World, A Book of Natural History Part 54

And this plan is also a great advantage to the anemone, which is sure to get plenty of food without any trouble. For when the crab finds the dead body of some small creature, and begins to pull it to pieces, a quant.i.ty of small fragments is sure to float upward in the water. And the anemone catches them with its spreading tentacles and feeds upon them.

THE ROBBER-CRAB

One of the most extraordinary crustaceans is this, which is found in many of the islands in the Indian Ocean. It is like the hermit-crabs in some ways, but the tail is covered with sh.e.l.ly plates, just like the rest of the body; and instead of living in sh.e.l.ls in the sea, it lives in deep burrows on dry land.

But the oddest thing of all with regard to this crab is its food. What do you think it feeds upon? Cocoanuts! That seems impossible, doesn't it? One would imagine that the crab could never get the nuts open. But it manages in this way: First of all, it pulls away the fibers from that end of the nut at which the three eyeholes are situated. With one of its stout claws it then hammers away at one of these till it breaks its way through. And finally, after allowing the milk to run away, it pokes its hind claws, which are very slender indeed, through the opening and picks out the white fleshy part of the nut a little piece at a time.

It is said, too, that this crab sometimes opens a nut by poking the smaller joint of one of its claws into the hole, and then striking it over and over again upon a big stone.

The burrow of the robber-crab is rather a deep one, and is nearly always situated beneath the roots of a tree. And at the end of the burrow is a large chamber, in which the crab piles up a quant.i.ty of cocoanut fiber to serve as a bed.

LOBSTERS

Of course you know the lobster very well by sight; and perhaps you know that until it is boiled it is black, not red. But do you know how it swims? If so, you know that it has two different ways of swimming. When it is not in a hurry it swims slowly forward by means of its swimmerets, of which it has five pairs under the hinder part of its body. But if it is startled or alarmed it swims swiftly backward by means of its tail.

If you look at a lobster's tail, you will see that it is very broad and flat, and that on either side of it are two plates, which are quite as flat, and, if anything, are rather broader. So, when these are spread, the tail looks like a fan. And the animal swims by first stretching out its body almost straight, and then doubling it suddenly with all its force. As it does so, the tail and the tail-plates spread out, and act very much like a broad oar. And the result is that the lobster darts swiftly backward through the water. Shrimps and prawns swim in exactly the same way.

Lobsters are very quarrelsome creatures, and are constantly fighting; and it very often happens that in these battles they pull off one another's limbs. They seem to feel very little pain, however, from such an injury, and before very long new legs begin to grow in place of the old ones, so that in course of time the wounded creatures are as perfect as ever.

Sometimes lobsters will throw off their limbs when they are not attacked at all. They do so, for example, if they are suddenly frightened; and it is said that if a heavy gun is fired near the surface of the water, every lobster for a long way round will shed its great claws in alarm.

You will notice, on looking at a lobster, that one of the great claws is a good deal smaller than the other; and sometimes people think that this is a new claw which is growing in place of one that has been lost, and that it has not yet reached its full size. This, however, is a mistake, for one of the claws is always much bigger than the other; and the reason is that they are used for different purposes. The larger claw is intended as a weapon, and with this the lobster fights. But the smaller one is chiefly employed as a kind of anchor, by means of which the animal can cling to the weeds or rocks at the bottom of the sea.

Lobsters are caught in pots made of basketwork, just as crabs are. But they are not nearly so dainty as crabs, and do not mind whether the bait is fresh or putrid. They are always very much attracted, too, by any object that glitters, and many a lobster has been lured to its death merely by one or two oyster-sh.e.l.ls hung up inside the pot in such a manner as to show the shining pearly interior.

CRAYFISH

The crayfish is a kind of fresh-water lobster, which is found commonly in many parts of the world, and numerously in the central and southern parts of the United States. Most species hide all day long under the projecting edges of big stones, or in holes in the bank, only coming out after nightfall to search for food. The British crayfish is said to be particularly fond of the deserted burrow of a water-vole, and as it sits inside it always guards the entrance with its great claws, striking fiercely at any enemy which may be bold enough to come within reach.

One, at least, of the American kinds sinks its own burrows, in the form of round holes in the soil of damp meadows. These holes go down to water, which the animal cannot live long away from; and a part of the soil dug out is piled about the mouth of the hole in a little tower or chimney, sometimes several inches high.

In Europe crayfish are eaten and regarded as a delicacy when properly cooked; and there is no reason why the American ones should not be equally good, but they are rarely if ever used as food by us. The flesh tastes like that of the lobster, but is more tender.

SHRIMPS AND PRAWNS

These are really only tiny lobsters, and if you examine them carefully you will find that their bodies are made in exactly the same way. They swim, too, by means of their tails, and dart about so swiftly that it is almost impossible to follow their movements. You may often find them in numbers in the pools which are left among the rocks by the retreating tide. But as they are almost colorless until they are boiled, it is very difficult to see them, and they look just like shadows darting to and fro in the water.

You can easily tell a prawn from a shrimp, for the beak which projects in front of its head is covered with sharp points, which are almost exactly like the teeth of a saw. It feeds upon the bodies of the various small creatures which die by millions every day. In this way it helps to keep the water of the sea pure. It feeds in a curious way, tearing off tiny sc.r.a.ps of flesh with the little pincers at the tips of the second pair of legs, and poking them into its mouth one after another. The sides of these limbs are covered with hairs, so that they form little brushes; and with these the prawn carefully cleans its body and limbs, rubbing off every little speck of dirt which may happen to cling to them.

SANDHOPPERS

You can hardly walk along a sand sh.o.r.e when the tide is rising without seeing sandhoppers leaping and twisting about in thousands. If you turn over a bunch of seaweed which has been flung up by the waves just above high-water mark, you are almost sure to find forty or fifty of these odd little creatures hiding under it. In some ways they are rather like shrimps. But they differ from them in having their eyes set on the head itself, instead of on little foot-stalks projecting from it. And they have no carapace, or sh.e.l.ly shield, covering the middle part of the body.

How do these creatures hop? By first doubling up their bodies, and then straightening them out again with a kind of jerk. It is exactly opposite, in fact, to the way in which shrimps and lobsters swim.

Sandhoppers do not follow the retreating tide, but bury themselves in the sand very soon after the waves have ceased to break over them. Even when the surface of the sand is quite dry you can find their burrows by stamping with your foot, when a number of little round holes will suddenly open all round you.

These creatures have wonderfully sharp little teeth, and if you allowed a swarm of them to rest for a little while on your handkerchief you would most likely find that it was full of tiny holes when you took it up. They will eat almost anything, either animal or vegetable, and are quite as useful as the shrimps and prawns in helping to keep the sea-water pure. But they have a great many enemies, for sea-birds, land-birds, crabs, and all sorts of other creatures, destroy them literally in millions.

THE FRESH-WATER SHRIMP

This shrimp is very much like the sandhopper in some ways. You may find it in numbers in almost any small stream or rivulet. It hides under stones, or in little crevices in the bank, darting out now and then to seize one of the tiny creatures upon which it feeds, and then hurrying back with it to its retreat. When it is in the water it travels along by a series of jerks; sometimes swimming with its back uppermost, and sometimes on one side. But if it is placed on dry ground it is perfectly helpless, for its legs are not nearly strong enough to carry it, and the only result of its struggles is to turn it round and round in a screw-like manner without forcing it forward at all.

WOODLICE

These odd little creatures are really crustaceans, although they belong to quite a different group from that about which you have just been reading. They simply swarm in all damp places. Under logs, in heaps of decaying leaves, and under the bark of dead trees, they are always extremely plentiful, and you may also find them in hundreds in cellars and outhouses. There are several different kinds, one of which rolls itself up into a ball when it is touched or alarmed. This is called the pill-woodlouse, or pill-armadillo. Another one is remarkable for the fact that the mother carries her little ones about with her in a pouch underneath her body for some little time after they are born.

BARNACLES

You would hardly think that barnacles were crustaceans, would you? Yet they are; though certainly they are very unlike any of those about which we have been telling. You can find them in countless thousands upon the rocks which are left bare by the tide at low water, and very often the hulls of ships are so covered with them that the vessels have to be taken into dry dock and thoroughly cleaned before they are fit to start upon a voyage.

These animals fasten themselves down to their hold by a kind of foot-stalk, which is firmly attached by a very strong cement. The upper part of the body becomes covered with a sh.e.l.l, consisting of several pieces, or valves; and between these, six odd little limbs can be poked out at will. These limbs are very hairy, and are always waving about, so as to sweep into the mouth any tiny sc.r.a.ps of food which may be floating in the water.

There are a great many kinds of barnacles, some of which look very much like acorns, and grow to a considerable size. These are known as acorn-barnacles. And there is another, shaped rather like a piece of round tube, which burrows into the skin of whales, in which it spends all the remainder of its life! Sometimes it bores its way down so far that it actually reaches the blubber.

The young of these strange creatures pa.s.s through several transformations, just like those of the lobster and the crab. First, there is a nauplius, then a zoea, and then a megalopa, all of which swim freely about in the water, never fastening themselves down until they are ready to pa.s.s into the perfect form.

CHAPTER x.x.xVI

SEA-URCHINS, STARFISHES, AND SEA-CUc.u.mBERS

Next in order to the crustaceans comes a group of animals which live in the sea, and which are known as echinoderms, which simply means spiny-skins. This group includes the sea-urchins, the starfishes, and the sea-cuc.u.mbers.

[Ill.u.s.tration: LIFE ON THE SEA-BOTTOM.

1. Sticklebacks. 2. Carp. 3, 5, 6, 13, 17. Sea-Anemones.

4. Shrimps. 7. Prawn. 8. Fiddler Crab. 9. Starfish.

10. Sea-horses. 11. Edible Mussels. 12. Serpula Worm.

14. Hermit-Crab in Whelk's Sh.e.l.l. 15. Sea-urchins. 16. Rock Crab.

18. Polyzoan (Fl.u.s.tra). 19. Corallines (Gorgonia).]

SEA-URCHINS

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 sh.e.l.ls are so thickly covered with spines that they look just like little hedgehogs which have rolled themselves up into b.a.l.l.s.

When the animal is alive it can move these spines at will, each of them being fastened to the sh.e.l.l by a ball-and-socket joint, just like those which we described to you when we were telling about the vertebrae 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 sh.e.l.l is left quite smooth and bare.