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.
[Illustration: PLATE XXVII
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.”
[Illustration: PLATE XXVIII
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.
[Illustration: PLATE XXIX
1. SANDHOPPER (enlarged).
1A. ” (life-size).
2. SAND SCREW (enlarged).
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.
[Illustration: PLATE XXX
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!