The Animal World, A Book of Natural History Part 55

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 sh.e.l.l 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 sh.e.l.l 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 sh.o.r.es of North America, because these sh.o.r.es 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 s.n.a.t.c.h 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-gla.s.s, you will see that they are shaped just like wine-gla.s.ses, each having a kind of fleshy cup at the end of a slender stem. And at the end of the cup is the sucker.

In the very middle of the lower part of the body of a starfish is its mouth. This is generally rather large, for the animal feeds chiefly on sh.e.l.l-bearing animals which it swallows whole, sh.e.l.ls and all. Then, when it has digested the bodies of its victims, it turns their empty sh.e.l.ls out again through its mouth. That is an odd way of feeding, isn't it? But sometimes it feeds in an odder way still, for when it finds a creature which is too big to be swallowed, it will actually turn its own digestive organs out of its mouth, wrap them round its victim, hold them there until it is digested, and then drag them in again and go off to look for another victim!

Starfishes eat a great many oysters in this way. So many do they destroy, indeed, that they are the very worst foes with which oyster-fishers have to deal, and the damage done by them in one single oyster-bed on the coast of North America is estimated at no less than fifty thousand dollars every year.

There are a great many different kinds of starfishes. One, for example, has twelve rays instead of five, and looks very much like a live sunflower. This is called the sun-star. Another has its five rays all joined together by webbing, very much like the toes on a duck's foot, and is known as the bird's-foot star. It is a very handsome creature, for while the greater part of its body is bright yellow, it has a broad band of crimson running all the way round the outer margin, and another stripe of the same color down the outer edges of each ray, while the membrane between them is fringed with yellow hairs. But you are not very likely to find it, for it lives in rather deep water, and is hardly ever caught except by means of that useful net which is called a dredge.

Odder by far than any of these, however, are the brittle-stars, which owe their name to their extraordinary habit of breaking themselves to pieces! They nearly always do this if they are touched or alarmed. In fact, they are so ready to do so that it is very difficult indeed to obtain a perfect brittle-star for a museum. The creature just gives a kind of shudder, and its five rays all drop off and break up into little pieces, all that is left of the animal being just the central disk. But it does not appear to suffer any pain, and loses hardly any blood.

And before very long new rays grow in the place of the old ones, so that in a few weeks' time the starfish is just as perfect as ever!

The brittle-stars have five very long and very slender rays, which are generally fringed on either side with yellow hairs. And these rays are hardly ever still, but twist and writhe and curl about so actively that they really look almost like so many centipedes! It is by no means so numerous as the fivefinger, and is so easily broken that it is hard to find a whole one on the beach.

Very curious, too, is the basket-star, which at first sight does not look like a starfish at all. The reason is that, close to its body, each of the five rays divides into two. Then each of the branches divides into two again, and each of those into two more, and so on over and over again, till sometimes there are more than eighty thousand little arms altogether!

The basket-star catches its prey by means of these wonderful rays, which it wraps all round it in the form of a circular basket. It is not at all a common creature, and is only found in deep water.

But perhaps the oddest of all these creatures is the rosy feather-star, which actually grows on a stalk while it is young, and looks just like a flower with its petals spread. The stalk, which is fastened down to a rock at the bottom of the sea, is made up of a great number of tiny joints, and grows longer and longer. And when it reaches its full length the animal breaks itself free and swims away, leaving the stem behind.

The rosy feather-star lives in rather deep water, from which it is sometimes brought up by means of the dredge. It can crawl about on the ground by means of its sucker-like feet, and can swim through the water with some little speed. And very often, to save itself trouble, it will cling by means of its rays to a piece of floating wood, and allow itself to be carried for long distances by the waves.

In Great Britain these may often be found near sh.o.r.e, but the American feather-stars all live in very deep water. They are all that remain of a large cla.s.s of such animals which abounded in the very ancient seas, whose fossil remains are called stone-lilies.

SEA-CUc.u.mBERS

These are really relations of the starfishes, although they do not look in the least like them; for they closely resemble the vegetable after which they are named. In front of the slit at one end of the body, however, which serves as a mouth, there is a feathery tuft. This consists of delicate little tentacles, or feelers, by means of which the animal fishes for its food, and which can be drawn back inside the body when it is not hungry. And if it were not for this tuft one really might almost mistake the animal for a grayish-white cuc.u.mber.

We saw just now that the brittle-star breaks off its own rays at the slightest alarm. But the sea-cuc.u.mber, in this way, is even odder still, for if it eats anything which disagrees with it, as it sometimes does, it turns all its digestive organs out of its mouth, cuts them off, and allows them to float away! Then for three or four months it is very little else than a bag of empty skin, with just a slit at one end and a tuft in front of it. But at the end of that time new digestive organs begin to grow in the place of the old ones, and very soon the sea-cuc.u.mber is as perfect as ever!

Isn't that a remarkable way of curing indigestion?

Some of the sea-cuc.u.mbers grow to a very great size. One indeed, when fully grown, is nearly six feet long. And in China they are largely used as food, under the name of trepang, and are looked upon as a great dainty.

CHAPTER x.x.xVII

MOLLUSKS

The cla.s.s of the mollusks is a very large one, for at least fifty thousand different kinds of these creatures are already known, while new ones are constantly being discovered. They may be described as soft-bodied, boneless animals, which are enclosed in a tough muscular skin called the mantle. And they are divided into five orders, the first of which includes the singular creatures known as squids, or cuttles.

You may sometimes find these animals hiding in the pools which are left among the rocks when the tide goes out; and you can recognize them at once by the long, fleshy tentacles, or arms, which spring from the upper part of the head. Some of them have ten of these arms, and are called decapods; the rest have only eight and are known as octopods. And the lower surface of each arm is furnished with a row of circular suckers, the grip of which is so powerful that the tentacle may even be torn in two without causing it to release its hold. Indeed, if quite a small cuttle were to seize you with one of its arms, you would not find it at all easy to make it let go again without killing it.

The cuttles employ these suckers for two purposes. In the first place, they use them in walking. When a cuttle is crawling along at the bottom of the sea it pushes one or two tentacles forward, takes firm hold of a rock or a large stone with the suckers underneath them, pulls up the body, and then thrusts them forward again. And in the second place, they use them in catching their prey. Quite large victims are often seized by cuttles, and when once the deadly suckers have fastened upon them there is no hope of escape. In spite of their struggles one tentacle after another comes closing in, till they are completely surrounded by the long, slimy arms, soft almost as jelly, yet strong as steel. Then they are pushed down against the sharp, strong beak, by which they are quickly torn in pieces.

On the upper part of the head of the cuttle there is another curious organ known as the siphon, which consists of two tubes lying side by side together, like the barrels of a double-barreled gun. This organ is used in three different ways.

First, it is used in breathing. The cuttles, like the fishes, breathe water, by means of gills. These gills lie inside the head, and the water pa.s.ses down to them through one of the siphon-tubes, and then out again through the other.

Next, it is used in swimming. When cuttles are not in a hurry they crawl along by means of their long tentacles, as we told you just now. But if they are startled, or alarmed in any way, they fold all their tentacles together in a straight line, fill both the siphon-tubes with water, and then squirt it out again as hard as they possibly can. The result is, of course, that they are driven rapidly backward by the recoil, just like the dragonfly grub, of which we have read.

But the third use of the siphon-tubes is the most curious. If you discover a small cuttle hiding in a rock-pool, you will very likely find that the water all round it suddenly grows dark as night, just as if a quant.i.ty of ink had been poured into it. The fact is this. Inside its body the cuttle has a bag filled with a quant.i.ty of a deep-black liquid called sepia. This bag is surrounded by strong bands of muscle, and opens into the siphon-tubes. So, you see, when the animal suddenly contracts the muscular bands, the sepia is squirted out through the siphon into the water, which is immediately darkened for some little distance all round. And under cover of the darkness the animal escapes.

The eggs of the cuttle are laid in a very curious way, for they are fastened by little stalks to a stem of seaweed, so that they look very much like a bunch of grapes. Fishermen, indeed, nearly always speak of them as "sea-grapes."

The cuttles which are found in the British seas are always quite small.

But in some parts of the ocean these creatures grow to a giant size.

Fragments of the tentacles of an enormous cuttle, for instance, have been found lying on the coast of Newfoundland; and by careful calculation it was shown that if the animal to which they belonged had stretched them out at right angles to its body, they would actually have measured more than eighty feet from tip to tip!

These huge creatures seem to form the princ.i.p.al food of the spermaceti-whale.

THE CHAMBERED NAUTILUS

This animal is a near relation of the cuttles. It lives in a sh.e.l.l, which cannot increase in size. The mollusk itself grows, however, and soon becomes too big to live in its home; so it forms a second and larger compartment outside the first one. Time after time this happens, till at last the sh.e.l.l consists of about thirty-six chambers, only the outside one being inhabited by the nautilus.

This sh.e.l.l is often more than a foot in diameter. But if you were to see it when it is first taken out of the sea you would never think that it was a sh.e.l.l at all. Indeed it looks much more like a big shapeless lump of blubber, for the animal covers it entirely with its muscular mantle, so that the sh.e.l.l itself is completely concealed.

Very little is known of the habits of the chambered nautilus, for it lives at the bottom of the sea, at a depth of two or three hundred fathoms. It is found in various parts of the Indian and Pacific oceans.

GASTROPODS

A great many well-known creatures belong to this large group, first upon the list being the slugs. We need not describe these animals, but perhaps you will be surprised to hear that they have sh.e.l.ls! These sh.e.l.ls are very small, however, and are entirely covered over by the mantle, so that they cannot be seen unless the body is dissected.

Slugs have the most wonderful power of stretching out and drawing up their bodies. You may see one of these creatures crawling about on a damp evening, and measuring fully five inches in length. But at the slightest touch it begins to contract, and in a few seconds it is just a shapeless lump, scarcely half as long as it was before. The odd little tentacles are drawn back into the head, and the head is drawn back into the body so that if you did not happen to know what it was you might easily mistake it for a pebble.

On the right-hand side of a slug's body, as it crawls along, you will notice a rather large and almost round hole. This is the entrance to the breathing-organs, which lie just behind the head and underneath the mantle.

During the daytime slugs remain in hiding, lying behind the loose bark of dead trees, or under logs and large stones, or in heaps of decaying leaves. And if the weather is very hot and dry they do not come out even at night, for they very soon die if they are deprived of moisture. But on warm, damp evenings they travel for long distances in search of food, which is almost entirely of a vegetable character. In Europe every gardener knows what injury they do to gardens there, but in America the slugs are practically harmless.