HOW CRABS HEAR AND SMELL
The way in which crabs hear and smell is almost as curious as the way in which they see, for they have very odd little ears and noses in very odd places.
On its head, as perhaps you know, a crab has two pairs of feelers. We call them the “lesser feelers” and the “greater feelers.” Now if you were to look at the first joint of the lesser feelers through a good microscope, you would find on each a little gland, or bag, containing a very tiny drop of salt and water. These are the crab’s ears. Of course they are not nearly so good as our ears are. Indeed, I do not think that a crab can hear sounds in the air at all. But water carries sounds much more readily than air does, so that if you were to dive into a lake, or into the sea, on a calm, still day you could easily hear the beat of the oars in a boat half a mile away. And the ears of the crab are made in such a way that they can hear sounds in the water quite well, even though they may be deaf to sounds in the air.
Then if you look at the first joint of the greater feelers through the microscope, you will see two other tiny glands. These are the crab’s noses, by which it can smell odours in the water just as we can smell odours in the air. It always seems to find its food by scent, and if one of those basket-like traps which we call crab-pots is baited with a few pieces of decaying fish and lowered into the sea, crabs will smell the bait from quite a long distance away, and come hurrying up to obtain a share in the banquet. And they seem to do so by means of those odd little noses on the lower joints of their greater feelers.
PLATE XXI
THE EDIBLE CRAB
Now let me tell you something about the different kinds of crabs which you may find on the shore.
First of all, of course, there is the Edible Crab. This is the crab which is so largely used for food, and which you may see in any fishmonger’s shop. Sometimes it grows to a very great size, and has claws so big and strong that if it were to seize a man by the wrist he would find it very difficult indeed to set himself free. You will not find crabs as big as this among the rocks, for these giant creatures always live in rather deep water. But one often discovers a crab four or five inches across hiding in a rock-pool, and even he is quite big and strong enough to give one a very sharp nip.
THE EDIBLE CRAB.
It is rather amusing to get one of these crabs out on to the open sand, and then to stand just in front of him. He will at once raise both his great claws and hold them in readiness to strike at you if you attempt to seize him. Then if you walk slowly round and round him he will turn round and round too, so as to keep facing you, over and over and over again. And if you put your hand anywhere near him he will snap at it so quickly that it is really not at all easy to avoid his stroke.
Edible crabs often have their shells covered with barnacles and the tubes of some of the sea-worms. Old crabs, indeed, which no longer change their coats of mail every year, are often so covered with these creatures that one can hardly see their shells at all.
PLATE XXII
THE SHORE CRAB (1)
This is sometimes known as the Green Crab, because it is generally more or less green in colour. But you may often find examples, which are deep brown all over, while others are bright yellow, with black markings upon their backs. It does not grow to nearly such a great size as the edible crab, and although its flesh is quite good to eat there is so little of it that the animal is hardly ever used for food. But it is wonderfully strong, and if you find a green crab hiding beneath a big stone or behind a mass of sea-weed, you must be very careful not to get a nip from its claws.
The green crab spends a great part of its life out of the water, for its gills are made in such a manner that they will keep moist for a very long time. And as long as its gills are damp a crab can breathe quite as easily on land as if it were in the sea. It is very active, and if you go down near the water’s edge while the tide is coming in you may often see it hunting sandhoppers and even flies, creeping up to them very carefully until it is only a few inches away, and then pouncing upon them so suddenly that they have no time to escape. And it is often very troublesome to fishermen, for it will seize their bait with its strong nippers, and pull it off the hooks before a fish is able to take it.
This crab is very easily kept in confinement, and will soon become quite tame, so that it will even come and take food from your fingers just like a dog. But you must be careful to pile up a few stones in the water in which you keep it, so that it may sit upon them and take an airing whenever it feels inclined. And it will even enjoy an occasional run about the room.
1. THE SHORE OR GREEN CRAB.2. THE FIDDLER CRAB.
PLATE XXII
THE FIDDLER CRAB (2)
The crabs about which I have been telling you live in the sea, though they often leave it for some little time and run about on the shore. But none of them can swim, and if they are thrown into deep water they just sink to the bottom with their legs sprawling, feeling about for some object to which they can cling. Sometimes, however, if you look into one of the pools which are left among the rocks when the tide goes down, you may see a small crab swimming through the water with some little speed. This is quite sure to be a Fiddler Crab, and if you catch it and examine its hinder legs, you will find that instead of being quite slender, with hooked claws at the tips, as they are in most crabs, they are flattened out into broad, oval plates. And you will also find that these plates have a fringe of rather long hairs growing all round them.
Now these are the paddles with which the crab rows itself through the water, and it is called the “Fiddler Crab” because the movements which it makes with them are rather like those of a man who is playing the violin. You can easily keep it in an aquarium, and a very interesting little pet it makes. But you must remember that it is a very savage little animal, and will certainly do its best to kill any other creatures that you may put into the same vessel. Even if you put two fiddlers together they are almost sure to fight; and the one which wins the battle will kill and eat the one which loses it.
When the Fiddler Crab is alive it is really a very handsome little creature, for its blackish shell is covered all over with soft, short down, looking rather like velvet, while its legs are striped with blue, and its claws are partly blue and partly scarlet.
PLATE XXIII
THE MASKED CRAB (1)
The broad shelly shield which covers the back of a crab is called the “carapace,” and there are certain markings upon it which are rather like the features of a human face. But there is one crab in which these markings are so deep and strong that it looks just as if it were wearing a mask. So it is always known as the “Masked Crab.” It is found on the southern and western shores of England and Wales, and you may always know it if you meet with it, not only because of the face-like markings upon its back, but also because its carapace is a good deal longer than it is broad, whereas in other crabs it is nearly always broader than it is long. Besides this, the great claws are not really “great” at all, for they are very long indeed and very slender, with quite small nippers at the tips, while the greater feelers are quite as long as the claws. So altogether the masked crab is a very odd-looking crab indeed. But if you want to find it you will have to look for it very carefully, for it has an odd way of burying itself in the sand, and only leaving just its feelers and its eyes above the surface.
PLATE XXIII
THE THORNBACK CRAB (2)
This is perhaps the very oddest of all our British crabs.
In the first place, it looks much more like a big spider than a crab; for its body is very small, while its legs are very long and very slender. Indeed, the group of crabs to which it belongs is often called “spider crabs” in consequence. In the second place, its carapace is covered all over with rather long sharp spikes, which project in all directions, so that it strongly reminds one of a tipsy-cake! And, in the third place, the crab nearly always has a number of tufts of sea-weed or sponge growing upon its back.
Perhaps you might think that these come there by accident. But they do not. The crab himself plants them there! If you keep him in an aquarium you may often see him doing so. First of all he turns one of his long claws over his back and scratches away at the carapace, so as to roughen the surface. Then he pulls up a little sprig of sea-weed or sponge and actually plants it on his shell, pressing the rootlets firmly down. And besides the spikes upon the shell there are numbers of tiny hooks, which help to hold it in position. Then the crab plants another piece of weed or sponge in just the same way, and so he goes on planting piece after piece until his back is completely covered.
Now why do you think he takes all this trouble?
Well, the reason is that he does not want to be seen; for he has a great many enemies, and he knows perfectly well that if he were to lie among the sea-weeds or sponges at the bottom of the sea they would be quite sure to notice him as they passed by, and then he would almost certainly be killed and eaten. So he clothes himself with either sea-weeds or sponges, as the case may be, and then feels that he is perfectly safe, and that as long as he keeps quite still even the sharpest eye will fail to notice him. And if you catch one of these crabs which is covered with sea-weeds and put it into an aquarium in which sponges are growing, it will very soon strip the weeds off its back and cover itself with sponges instead; while if you catch one that is covered with sponges, and put it into a tank in which sea-weeds are growing, it will strip off the sponges and cover itself with sea-weeds!
1. THE MASKED CRAB.2. THE THORNBACK CRAB.
The thornback crab often grows to a rather large size. Indeed, next to the edible crab, it is the largest of all the crabs which are found in our British seas, for its carapace is sometimes as much as eight inches long and six inches wide, while its great claws may be fourteen or fifteen inches in length. On some parts of the coast it is used for food, but its flesh is rather coarse and of poor quality.
PLATE XXIV
THE LONG-BEAKED SPIDER CRAB (1)
This crab has an even smaller body in proportion to its size than the thornback, and its legs are so very long and so very slender that they remind one of those of a daddy-long-legs. Its carapace is drawn out in front into a kind of beak, which is quite as long as the carapace itself, and while the crab is alive it is of a most beautiful pink and puce colour. It is not a very common creature, but is sometimes to be found in the rocky pools near low-water mark on our southern coasts, and is covered, very often, with sea-weeds or sponges, just like the thornback.
PLATE XXIV
THE FOUR-HORNED SPIDER CRAB (2)
Perhaps this is the commonest of the British spider crabs. Indeed, it is so plentiful at Bognor, and at other places on the southern coast of England, that when a crab pot is taken out of the water as many as twenty or even thirty of these creatures are sometimes found in it. They are called by the fishermen “sea-spiders,” and are generally so clothed with those odd sea-weeds called “corallines” that you can hardly see any part of their “shells” at all.
In this crab the carapace is drawn out in front into a very long beak indeed, which has four horns upon it, and the whole upper surface is covered with short, sharp spikes and stout hairs.
1. THE LONG-BEAKED SPIDER CRAB.
2. THE FOUR-HORNED SPIDER CRAB.
PLATE XXV
THE PEA CRAB (1)
This is a very odd crab indeed. In the first place it is extremely small. Even when it reaches its full size it is scarcely ever so much as half-an-inch across, while its body is so round that it really does remind one very much of a pea. Only it is not quite the right colour for a pea, for it is creamy yellow instead of green.
And, in the second place, this crab lives in a very odd place—namely, inside the shells of living mussels, or pinnas, or even cockles! What it does there nobody seems quite to know. It does not appear to injure the animal to whom the shell belongs, although it is very fond of the flesh of mussels, and if it finds one of those creatures lying dead will certainly devour it. Perhaps it only creeps inside its shell for the sake of safety. At any rate, it is a very timid little crab, and if you open a mussel and find a pea crab lying hidden inside it, it will tuck up all its legs quite close to its little round body and lie perfectly still for several minutes in the hope that you will think that it is dead.
On some parts of the coast pea crabs are so plentiful, that three out of four mussels are found to have one of these odd little creatures inside it.
PLATE XXV
CRAB CATERPILLARS (2 and 2 A)
I dare say you did not know that crabs have caterpillars, just as insects have. We call these crab caterpillars “zoeas,” and they are not in the least like their parents. There are a great many different kinds, of course, for every crab has its own zoea, just as every butterfly and moth has its own caterpillar, and some of them are not very much like some of the others. But they are always very tiny indeed—they are scarcely as large, in fact, as the smallest grains of sand—and they always have a very long curved horn in front of the body and another one behind, and long waggly tails. And they swim in the oddest way possible—by turning somersaults in the water, over and over again!
These zoeas are very useful little creatures, because they feed upon the tiny scraps of decaying matter which are always floating about in the sea, and so help to keep the water always pure. They belong, in fact, to the great army of what I always like to call “nature’s dustmen”—those little animals whose duty it is to clear away the rubbish from the world. There are millions and millions of these busy little workers on the land, and millions and millions of others in ponds and rivers, as well as in the sea, and so well do they perform their task that both the air and the water are always kept pure.
Another very interesting fact about zoeas is that they form the chief food of no less a creature than the Greenland whale. No doubt you know that whales are of two kinds—those which have teeth, and those which have none. Those which have teeth feed upon fishes, and giant cuttles, and could easily swallow a man. But the whales which have no teeth have throats so small that they would almost certainly be choked if they tried to swallow a herring! So they have to feed on very small creatures indeed, and are very fond of zoeas, which often swim about in such vast shoals that the water of the sea is quite thick with them. And they catch them in a most curious manner.
You have heard, of course, of the very useful substance which we call “whalebone;” and no doubt you know that it has nothing to do with the bones of the whale at all. It is found in the mouths of those whales which have no teeth, and hangs down in great plates from the gums of their upper jaws. Very soon these plates split up; and then each part splits up again; and so on, over and over again, till at their lower ends they form a kind of thick fringe of close, matted hairs.
Now it is by means of this fringe that the whale catches the zoeas. When it meets with a shoal of these little creatures it opens its huge mouth wide, and swims through them. Then it nearly closes its jaws, and lets down the whalebone plates, so that the hairy fringe forms a kind of strainer all the way round. It then squirts out the water from its mouth through this fringe, which allows the water to pass through it, but keeps back the zoeas; and when it has got rid of all the water it closes its mouth completely and swallows the zoeas, a few thousand at a time, after which it opens its jaws again, and swims through the shoal once more.
Doesn’t it seem strange that the biggest animal on earth should feed on some of the very smallest?
PLATE XXV
CRAB CHRYSALIDS (3 and 3 A)
When the caterpillar of an insect has reached its full size it throws off its skin and appears as a chrysalis, or pupa. And the caterpillar, or zoea, of a crab does exactly the same thing. It casts its skin, and appears in quite a different form. Only we do not call it a chrysalis, as a rule. We call it a “Megalopa.”
1. PEA CRAB (life-size).
2. CRAB CATERPILLAR (enlarged).3. CRAB CHRYSALIDS (enlarged).
2A. ” ” (life-size).3A. ” ” (life-size).
The word “megalopa” means “a creature with big eyes,” and it is given to the crab chrysalis because it has eyes which are enormously big in proportion to the size of the head. They are set on long footstalks, which project on either side, so that the head looks rather like a hammer. Then the long curved horns which the zoea had are to be seen no longer, and the carapace is shaped much more like that of the perfect animal, while the great claws begin to show, and the legs increase in length. The tail, however, is still quite free, like that of a lobster, and the little animal still swims by turning somersaults in the water, and lives on the same tiny scraps of decaying matter on which it fed as a zoea. After a few weeks it throws off its skin once more, and appears in the world as a perfect crab.
PLATE XXVI
HERMIT CRABS (1 and 2)
If you go down among the rocks when the tide is out, and hunt about in the pools, you may often find the shell of a whelk in which a small crab is living, with one of his great claws carefully guarding the entrance. This is a Hermit Crab, and a very curious little creature he is. For, in the first place, his long tail is quite free, like that of a lobster, instead of being fastened down to the lower surface of his body; and in the second place, it is quite soft, without any shelly covering at all. His body and limbs are covered with armour, just like those of other crabs, but his tail has none at all.
The consequence is that the hermit crab always has to take the very greatest care of his tail. He is so dreadfully afraid that one of his many enemies will come up behind and give it a nip when he isn’t looking! So he protects it by tucking it away into the empty shell of a whelk. He never leaves this shell, but drags it about with him wherever he goes. And if you take hold of him and try to pull him out, you will find that you cannot do so without injuring him very badly. For at the end of his tail he has a pair of strong pincer-like organs, with which he holds on so firmly that it is very difficult indeed to make him let go.
Indeed, the only way to get a hermit crab out of his dwelling is to put him, shell and all, into the spreading arms of a big sea anemone. That frightens him almost out of his wits, for the arms of the anemone at once come closing in, and he knows quite well that if he stays where he is he will very soon be swallowed. So he skips out of the shell and scampers away as fast as he possibly can, leaving the empty shell in the anemone’s clutches.
1. THE HERMIT CRAB IN WHELK-SHELL.
2. THE HERMIT CRAB OUT OF SHELL.
The poor little animal is now perfectly miserable. He has no protection for his tail, you see, and goes hunting about everywhere for some other shell into which he can tuck it. After a while, perhaps, he finds that of a periwinkle. It is not of much use, of course, for it is so small that he can only get just the tip of his tail into it. Still, it is better than nothing, and he goes crawling about with the periwinkle shell on the end of his tail, like a thimble on the tip of one’s finger, in search of a bigger one. By-and-by he discovers one. Then he whips his tail out of the old shell and into the new one so quickly that you can hardly see how he does it, and goes off to look for a bigger shell still. And in this way he will change his dwelling perhaps half-a-dozen times before he is really satisfied.
Sometimes you may find a hermit crab with a sea anemone fastened to the edge of the shell in which he is living. That seems strange, doesn’t it, when you remember how terribly afraid the little animal is of anemones. But in such a case the anemone never interferes with the hermit crab, and the crab never interferes with the anemone, while both of them benefit by the arrangement. The crab benefits, because no fish will ever touch him so long as an anemone is attached to his whelk-shell. There are plenty of fishes which would be quite ready to gobble him up, whelk-shell and all, if it were not for this creature. But fishes know quite well that sea anemones can sting, and therefore never think of devouring them, no matter how hungry they may be; so that so long as an anemone is guarding the whelk-shell in which he lives, the hermit knows that he is perfectly safe. And the anemone benefits, because it gets a share of the crab’s meals. When a hermit crab finds the dead body of some small creature at the bottom of the sea he pulls it to pieces and devours it; and as he does so a quantity of tiny scraps are sure to come floating upwards, and are seized by the outspread arms of the anemone. So the crab gets the big pieces, and the anemone gets the little ones; and both are perfectly satisfied.
CHAPTER V
LOBSTERS AND THEIR KIN
PLATE XXVII
THE LOBSTER
YOU are not at all likely to catch a lobster for yourself, for these creatures live in deep water, and are only to be taken by means of proper lobster-pots. But I must not pass the animal by without mentioning it at all, for at any rate you will be quite sure to see it on the slab of every fishmonger’s shop.
Of course you know that a lobster is not red until it is boiled, but is nearly black all over. And of course you know, too, that one of its great claws is always a good deal larger and stouter than the other. Sometimes people think that the reason of this is that at some previous time the animal had lost one of his claws through some accident, and was growing a new one, and that the new limb had not yet had time to reach its full size. However, this is not the case, for one claw of a lobster is always a good deal bigger than the other; and the real reason is that the two claws are used for different purposes. The larger claw is a weapon, with which the animal fights, while the smaller one is an anchor, with which he clings to the weeds which grow on the rocks at the bottom of the sea. And very often one is quite twice as big as the other.
Now I wonder whether you know how a lobster uses his tail. He employs it in swimming, and if you look at it you will find that it is made of several broad, flat plates, which can be spread out very much like the joints of a fan. You will notice, too, that these joints have a fringe of hairs growing all round them. Now when a lobster swims he just stretches his body straight out, and then doubles it suddenly up. As he does so the plates of the tail spread out, and form a kind of very broad and powerful oar, which strikes the water with such force as to drive the animal swiftly backwards. With a single stroke of its tail, indeed, a lobster can dart to a distance of forty or fifty feet, and that so quickly that even the swiftest fishes could scarcely overtake him.
Sometimes, however, a lobster swims forwards; and he does this by means, not of his tail, but of five pairs of odd little organs underneath the tail, which we call “swimmerets.” They spring from either side of the soft hinges by which the joints of the tail are fastened together, and each consists of two thin oval plates fringed with long hairs. So each swimmeret really consists of two tiny paddles, and by waving them to and fro in the water the lobster manages to travel along with some little speed.
THE LOBSTER.
These swimmerets are used for another purpose as well, however, for the mother lobster always glues her eggs to the hairs with which they are fringed, and carries them about with her for some little time. Haven’t you noticed, when you have had shrimps for tea, that a good many of them had clusters of eggs underneath their bodies? Well, if you had put one of those shrimps under a microscope, and examined it very carefully, you would have found that every one of the eggs was firmly glued down to one of the hairs on its swimmerets, where it would have remained until it was hatched. And lobsters carry their eggs about with them in just the same way.
PLATE XXVIII
THE PRAWN (1)
If you go down among the rocks when the tide is out, and look into the shallow pools which have been left among them by the retreating waves, you are quite sure to see numbers of shadowy forms darting to and fro through the water. A good many of these will be prawns, and if you catch one or two of them in a small net, and examine them carefully, you will find that they are very much like tiny lobsters. Indeed, if you could magnify a prawn to the size of a lobster, or reduce a lobster to the size of a prawn, it really would not be very easy to tell the one from the other.
But you will be surprised to see how different live prawns look from the dead ones which you may see in a fishmonger’s shop. The fact is that, like the lobster, they change colour when they are boiled. When they are alive, indeed, they hardly have any colour at all, and are nearly transparent. That is why it is so difficult to see them in the water. And if you keep them in an aquarium, all that you can see of them, very often, as they dart to and fro is just their glowing eyes, which gleam in the water like tiny balls of fire.
There are two facts about prawns which I am sure you will be interested to know.
The first is that they are extremely useful little creatures, for they feed upon the bodies of the various small animals which die in the sea, and so prevent them from becoming putrid and poisoning the water. And the second is that they always take the greatest possible care to keep themselves clean. If you take a few live prawns home, and put them in an aquarium, you may often see them performing their toilets. Their front legs are covered with stiff little hairs which stand out at right angles, so that these limbs really form a pair of brushes. And with them the prawn will clean its body most diligently, rubbing itself all over until every little speck of dirt has been removed. And if any object should cling to its body which these tiny brushes cannot rub away, it will pull it off by means of the strong little pincers on the second pair of legs.
Do you want to know how to tell a prawn from a shrimp?
Well, all that you have to do is to look in front of its head. There, projecting from the edge of the “carapace,” or shield which covers the back, you will see a long spike, something like a beak. Just put your finger upon this, and feel the edge. If it is set with sharp little teeth, like those of a saw, the animal is a prawn. But if the spike is perfectly smooth, it is a shrimp.
PLATE XXVIII
THE ÆSOP PRAWN (2)
This is a much prettier creature than the common prawn, for its transparent body is covered with scarlet lines, while its long thread-like feelers have rings of the same colour round them at regular distances apart. It is called the “Æsop” prawn because it has a big hump on its back, just like the writer of the famous fables.
If you want to catch an Æsop prawn you must look for it in the summer, for it always spends the rest of the year in deeper water. But as soon as the weather becomes really warm it travels up and down with the tide, and you may find it in plenty in the pools which are left among the rocks at low-water.
PLATE XXVIII
THE SHRIMP (3)
I told you that a good many of the shadowy forms which you may see darting to and fro in the rock-pools are those of prawns. The rest are quite sure to be shrimps, which are very much more common. Indeed, in most of the rock-pools you will find at least ten shrimps for every prawn. But they are very difficult to see, for they are partly transparent when they are alive, so that they are scarcely visible when they are swimming. And when they are resting at the bottom of the pool their speckled bodies look almost exactly like the sand on which they lie. Besides this, they have a way of nearly burying themselves, by scooping out a kind of furrow with their hind limbs, sinking into it, and then covering themselves with sand by means of their feelers. So the fishermen often call them “sand-raisers.”
1. THE PRAWN.2. THE ÆSOP PRAWN.3. THE SHRIMP.
PLATE XXIX
THE SANDHOPPER (1 and 1 A)
Commoner even than the shrimps are the Sandhoppers. On any sandy part of the shore you may find them in thousands and thousands. If you walk along the beach where the sand is dry, and step rather heavily, you will see their holes opening all round you. If you walk along it where it is damp, you will find that it is honeycombed with their burrows. If you turn over a stone, or lift up a piece of sea-weed which has been thrown up by the waves, twenty, or thirty, or forty of them will come skipping out like so many tiny kangaroos. And if you walk near the edge of the water when the tide is coming in you may often see them leaping about in such vast numbers that they look just like a thick mist rising for a foot or eighteen inches into the air.
Yet sandhoppers have so many enemies that it really seems wonderful that any of them should be left alive at all. Nearly all the shore birds feast upon them, and so do many of the land birds. Indeed, when the tide is rising, you may often see a long line of birds standing closely side by side together a few feet in front of the water’s edge and gobbling up the active little creatures in thousands. Then the shore crabs are very fond of them, and destroy thousands more. And even when they are buried deeply in the sand they are not safe, for there is a little beetle which goes down their burrows after them, and catches and eats them there very much as a ferret catches a rabbit in its hole.
But it is just as well that they do not all get eaten, for sandhoppers are very useful little creatures indeed. They feed upon the masses of decaying sea-weed which are constantly flung up on the shore by the waves. For they, too, belong to the great army of “Nature’s Dustmen,” like the “zoeas” of the crabs and lobsters, and help to clear away all kinds of rubbish which would poison the air and the water if it were left to decay. Indeed, they will eat almost anything, and if you were to tie up a number of sandhoppers in your handkerchief, and leave them there for a few minutes, you would never be able to use the handkerchief again; for you would find that their sharp little jaws had nibbled it into holes.
If you watch a sandhopper carefully when it is skipping about, you will find that it leaps by doubling its body up, and then straightening it out again with a sudden jerk.
1. SANDHOPPER (enlarged).2. SAND SCREW (enlarged).
1A. ” (life-size). 2A. ” (life-size).
PLATE XXIX
THE SAND SCREW (2 and 2 A)
If you follow the tide as it goes out on a still day, you will notice that it leaves the sand quite smooth behind it. But if you come to the same spot about half-an-hour later, you will often find that it is marked by numbers of winding tracks, which look just as if they had been made by worms. These, however, are the work of the Sand Screw, a curious little creature which in many ways is very much like a sandhopper. But instead of sinking its burrows almost straight downwards into the sand, as sandhoppers do, it drives them along almost as a mole does, just below the surface.
If you stand quite still for a few minutes near the water’s edge, when the tide is going out, you may sometimes see this odd little creature at work; for as it pushes its way along it raises the sand into a kind of low tunnel, which generally falls in behind it, and so forms a groove. And if you suddenly turn over the sand in front of the tunnel you will find the little animal which was making it, and will see at once why it is called the “sand screw.” For instead of skipping about like a sandhopper, it will lie on one side and wriggle its way along with a curious “screwing” movement, just as though it were trying to bore its way into the sand.
PLATE XXX
ACORN SHELLS (1)
If you examine the rocks which are left dry when the tide goes out, you will often find that they are covered almost all over with small shells which look rather like those of tiny limpets. Only at the top of each shell there is a little hole, from the margin of which a number of ridges run down to the bottom. And these ridges are so sharp, that if you happen to slip when you are wandering about among the pools, and catch at a rock to save yourself, they will cut your fingers almost as if they were knives.
These creatures are generally known as “Acorn Shells,” and I dare say that you might think that they must be very closely related to the limpets. But in reality they are much more closely related to the shrimps and sandhoppers, though they look so very unlike them, and lead such different lives. For while shrimps and sandhoppers are always swimming or skipping about, the little animals which live inside these acorn shells never move at all after they are a few days old, but spend their whole lives fastened down to the surface of the rocks. But there is this great difference between the two. When the eggs of a limpet hatch, out come a number of very tiny limpets, just like their parent in everything except size. But when the eggs of an acorn shell hatch, the little creatures which come out from them are not like their parents at all. They are “zoeas,” in fact, or acorn shell caterpillars; and they do not reach their perfect form for some little time.
When these little “zoeas” first make their appearance in the world they are able to swim about by means of three pairs of tiny feathery legs, with which they paddle their way along through the water. And they also have a round black eye in the middle of the body, with which they can see quite well. Every two or three days they throw off their skins, just as caterpillars do, and appear in new ones, which have been gradually forming beneath. And each time that they do this their shape changes. At last they are ready to take their perfect form. Then each of the little creatures clings to the surface of a rock by means of its feelers, and pours out a kind of cement, which hardens round them, and anchors it firmly down. It then throws off its skin once more, and appears in the form of an acorn shell just like its parent. And, strange to say, it throws off its eye at the same time, and is perfectly blind for the rest of its life!
If you look down into a shallow pool, the rocky sides of which are covered with these acorn shells, you may often see a very pretty sight. You may see the little animals fishing. Out from the hole at the top of each shell comes a kind of little net, which sweeps through the water, and is then drawn back into the shell. This net is really formed by the limbs, which are fringed with long hairs, and as it passes through the water it collects the little tiny scraps of decaying matter on which the animal feeds.
You may find these acorn shells in great numbers, not only on the rocks which are left dry when the tide goes out, but also on the wooden beams which support piers and jetties. Indeed, these beams are often so closely covered with the odd little shells that you cannot see the surface of the wood at all. And very often they fasten themselves to the shells of limpets and oysters, and even on the backs of crabs.
1. ACORN SHELLS.2. SHIP BARNACLES.
PLATE XXX
SHIP BARNACLES (2)
These creatures are first-cousins, so to speak, of the acorn shells, and they are called “Ship Barnacles” because they are so very fond of fastening themselves to the bottoms of ships. Even after two or three months, indeed, the hull of a vessel is often quite covered with them below the water-line, and they check her speed so greatly that she has to be taken into dock to have them scraped off before she can set out upon another voyage.
You may generally find quite a number of these barnacles on the pieces of timber which are so often flung up by the waves after a storm. And you will notice that each of them grows, as it were, upon a kind of stalk, instead of being fastened down to the surface of the wood, as the acorn shells are upon the rocks. This stalk consists of the pillar of cement with which the little animal covered its feelers just before it changed its form for the last time.
There are a good many other kinds of barnacles, some of which are found in very odd places. There is one, indeed, which always lives on the backs of whales, and somehow manages to sink itself quite deeply into their skins!
CHAPTER VI
THE SEA WORMS
PLATE XXXI
THE SEA MOUSE (1)
IF you go down among the rocks when the tide is out, and hunt in the muddy pools near low-water mark, you will be almost sure to find a very odd-looking creature indeed. It is generally between three or four inches long, and although it is called a “Sea Mouse” it looks very much more like a hairy slug; for its whole body is covered with a matted coat of bristles. But it is really a kind of sea worm. And it looks just about as dull and dingy as any creature can possibly be.
Yet in reality it is one of the most beautiful animals which are found in the sea, and if you want to see its beauty, all that you have to do is to wash it. For the bristly coat which covers its body is a kind of filter, which strains out the mud from the water which passes to the gills; and it soon becomes so choked with mud that you cannot see what the animal is really like at all. All that it wants, however, is a really good bath: so just take it to a pool of clear sea-water, and rinse it thoroughly. Then take it to another pool, and rinse it again. Then take it to a third pool, and rinse it again; and go on rinsing it till every atom of mud has been washed out of its hairy coating. And then, if you look at it in the bright sunshine, I am quite sure that you will be astonished to find what a lovely creature it really is. For all the colours of the rainbow, and ever so many more besides, seem to be chasing one another over its bristles, and altering with every movement and every change of light. Doesn’t it seem strange that an animal so beautiful as this should live with all its beauty covered up, so that hardly any eye can ever see it?
But these bristles have another use besides that of a filter. Each of them is really a kind of long, slender spear with a barbed tip, which can be used as a weapon of defence. If you were to look at one of these bristly spears through a good strong microscope you would see that it was edged on both sides with sharp little hooked teeth, looking very much like those of a shark. But you need not be in the least afraid to handle a sea mouse, for although these slender spears look so formidable, they are not nearly strong enough to pierce your skin.
1. THE SEA MOUSE.2. THE SABELLA.
PLATE XXXI
THE SABELLA (2)
A good many different kinds of worms live on the sea-shore, and one of the most curious of these is the Sabella. For it lives in long, narrow tubes made of tiny grains of sand, which it sticks together with a kind of natural glue. You may find these tubes in great numbers just about low-water mark, and hundreds and hundreds of them are often twisted up together in great masses, which are sometimes several feet in diameter. The worms can travel up and down these tubes by means of tufts of stiff little bristles on each side of their bodies; and sometimes they will leave them altogether, crawl about on the sand for a little while, and then make new ones. And if you keep them alive in a glass vessel filled with sea-water, with a little sand at the bottom, you can watch them building their wonderful tubes, carefully choosing grains of sand of just the proper size, arranging them in position just as a bricklayer lays bricks, and then sticking them firmly together.
PLATE XXXII
THE SERPULA (1 and 2)
If you look down into the pools among the rocks when the tide is out you may often see a number of long, twisted tubes fastened to the surface of the stones at the bottom. These are the dwellings of a very curious sea-shore worm called the Serpula, and if you lift one of the stones out of the water, and look down into the tubes, you will nearly always see a bright scarlet object lying just beneath the entrance. And then you may be quite sure that the animal is alive.
Now suppose that you carry the stone home with you, just as it is, and put it into a vessel of sea-water. After an hour or two you will find that the little scarlet objects have been poked out of the tubes, and that they are really tiny stoppers, just like little corks, which exactly fit the entrance when they are pulled inside. And you will also find that a plume of feathery objects, which are also bright scarlet in colour, is projecting out of the mouth of each tube. These red plumes are the gills of the worms, and they will often remain spread for hours at a time. But if you startle the animals—if your shadow falls upon them, for instance—they will draw themselves down into their tubes in about half a quarter of a second, and every tube will be corked up by its tiny stopper, just as before.
1. THE SERPULA.2. SERPULAS IN TUBES.
On the sides of its body the serpula has tufts of little bristly hairs, just as the sabella has, which allow it to move up and down its tube. But in order to enable it to draw itself back as quickly as possible in moments of danger, it has a row of little hooked teeth on its back, by means of which it can take a firm hold of the lining of its burrow. I think you will be rather surprised when I tell you how many of these teeth there are in the row. Just fancy! Each serpula has between thirteen and fourteen thousand!
If you look at the oysters in a fishmonger’s shop, you may often see the tubes of these curious worms fastened to the surface of the shells.
PLATE XXXIII
THE TEREBELLA (1)
This is another of the worms which live in tubes. You can generally find its wonderful little dwellings by hunting in the small puddles of sea-water which are left on the sands when the tide goes out. And you can always tell them from those of the sabella and the serpula by the curious little fringe round the entrance, which is made of the tiniest grains of sand fastened together into slender threads. The tube itself is made of larger grains, and is so tough and leathery that you can give it quite a hard pull without breaking it. But as it is at least a foot long, and is nearly always carried down underneath rocks or big stones, you will not find it at all easy to dig it up. And the moment that you alarm the little animal inside it always makes its way right down to the very bottom of its tube.
Sometimes a terebella will leave its tube and go for a little swim in the pool, wriggling its way through the water by first doubling its body up and then stretching it out, over and over again. But it very soon gets tired with its exertions, and sinks down to the bottom of the pool to rest. Then, after awhile, it will set busily to work, and make a new tube to live in instead of the old one.
There is another kind of terebella, called the Shell-binder, which makes its tube of little bits of broken shell instead of grains of sand. You may find the ends of these tubes sticking up out of the sand about half-way between high and low-water mark. But they run down so deeply that you will have to dig very hard indeed if you want to get them out of the ground.
1. THE TEREBELLA.2. THE LUG WORM.
PLATE XXXIII
THE LUG WORM (2)
On any muddy stretch of beach, when the tide is out, you may see numbers and numbers of little twisted casts, just like those which you may find on the lawn in the garden on any warm damp morning. These are made by Lug Worms, or “logs,” as the fishermen generally call them, and they really consist of sand which the worm has swallowed during the last three or four hours. For lug worms burrow by swallowing mouthful after mouthful of sand, until they can swallow no more. They eat their way down into the sand, in fact, just as earth-worms eat their way down into the ground. And when their bodies are quite filled with sand, they come up to the entrances of their burrows and pour it out in the little twisty coils which everybody who has walked on the shore knows so well by sight.
If you take a spade and dig down into the muddy sand you can find these worms in great numbers. They are just about as big as earth-worms, and are of all sorts of colours, some being brown, and some dark green, and some purple, and some crimson. But on each side of the body they always have thirteen pairs of bright scarlet tufts. These are the little gills by means of which they breathe, and if you put them under a microscope they look just like tiny bushes with brilliant red leaves.
You would think, perhaps, that when a lug worm bores its way through the loose sand, the sides of its burrow would fall in behind it as fast as it passed along. But from the surface of its body it pours out a thin, sticky liquid which binds the sand together, and forms a kind of lining to the burrow, like the brickwork of a railway tunnel. The burrow is generally about two feet deep, and the worm always lives in it with its head downwards. The worm itself, when fully grown, is from six to ten inches long.
PLATE XXXIV
THE NEMERTES (1)
This is quite one of the most curious creatures to be found on the sea-shore. It hides under large stones at the bottom of the pools, and looks rather like a tangled boot-lace. But it is really a kind of leech-like worm, and the wonderful thing about it is that it can stretch its body out to almost any length, just as if it were made of elastic. It always does this in catching its prey, which it seizes by means of its sucker-like mouth, which has a kind of beak inside it. Then it “plays” its victim just as an angler “plays” a fish, sometimes stretching its body out to a length of fifteen or twenty feet, then drawing it in again to a length of three or four, and so on over and over again, until its prisoner is quite exhausted, when it proceeds to devour it.
PLATE XXXIV
THE NEREIS (2)
The Nereis is a very common sea-side worm, and you can nearly always find it by turning over the stones on the shore as the tide goes out. It is brown in colour, with a dark red line along the back; and if you look at it in the sunlight you will see flashes of bright blue playing over the surface of its skin. And underneath it is of the most delicate pink, with a glossy look which reminds one of mother-of-pearl. It is one of the largest of all the worms, for it often grows to a length of nearly two feet.
If you examine the back of a nereis, you will find a row of little tufted organs running right along it. Each of these really consists of two little flaps, which are folded together as long as the worm remains still. But as soon as it begins to swim they open out and wave up and down in the water; for they are really tiny paddles, by means of which the nereis rows itself along. Altogether there are about four hundred pairs of these little flaps, which move in perfect time together, just like the oars of a well-rowed boat. Perhaps you may have seen a boat-race, and you noticed, no doubt, how all the eight oars rose and fell exactly at the same instant, as regularly as if they were moved by machinery. Well, imagine a very long boat indeed rowed by four hundred little rowers instead of only by eight, and each with two oars instead of one, and then you will have some idea of what a nereis looks like as it goes swimming through the water.
This curious worm does not live only under stones, for it is sometimes found hiding in the whelk shells which are occupied by hermit crabs, the worm and the crab living in the same shell together, and never seeming to interfere with one another.
1. THE NEMERTES.2. THE NEREIS.