SHRIMPS AND PRAWNS.
Popularly there are about three British species of shrimps, including
the Prawn; and the reader whose knowledge of our Crustacea is slight
will look for a very brief chapter this time. But he who has paid a
little attention to this group will know that we have a difficulty
before us in giving anything like a reasonable account of British
shrimps without the chapter running into a book. However, our task is
greatly lightened for us by the fact that many of these are to be found
only in deeper water than lies within the littoral zone, and therefore
must be excluded from our survey. By a course of proceeding then from
the known to the unknown, we would call attention to the largest of the
well-known trio.
The Great Prawn (_Leander serratus_), which we fear is best known in
its brilliant red colouring, as seen on the breakfast tables of the
well-to-do, and in the shop of the first-class fishmonger. Neither of
these places offers great advantages for the pursuit of natural history
studies so far as the external appearance of living creatures is
concerned. It is in the rock-pools that we must make our acquaintance
with the noble Prawn in all the glow and glory of life and activity. It
is true he then lacks the fine colour of the boiled article, but he has
the greater beauty with which Nature has endowed him; and when you have
seen him in his native haunt you will confess that we have not misused
the term “noble” in applying it to the bearing of the Prawn.
Not many years ago a learned Professor wrote a book on the sea-shore,
and in it stated, among many other curious things, curiously said,
that the Prawn could scarcely be called a shore animal except in its
younger condition. Probably he had got most of his natural history from
the University, and his Professorial dignity would not allow him to go
on hands and knees beside a rock-pool that he might learn of the living
creatures there: for in all the pools on a rocky coast, Prawns of all
sizes, including the giants of the species, are very plentiful.
The young prawns, though somewhat lacking the grandeur of the older
ones, are more beautiful; their shelly armour is so crystalline, and
their flesh is so clear. But with adult-growth comes a thickening of
the armour-plates, and a very pale brown coloration produced by the
greater density of the muscular tissue with which it is principally
filled. You cannot help being struck with the pretty colouring of those
limbs which the late Thomas Bell called the Prawn’s hands; these are
the limbs that are furnished with nippers or pincers at their ends, of
which the Prawn has two pairs. The first two are very delicate organs,
and are only used for delicate work. The second pair the Prawn always
carries in front of him, ready for action, but the first are carefully
folded up and held close under the jaws. In an aquarium where you have
introduced a mossy-looking stone from low-water, you will see the Prawn
ranging over it and picking up with his smaller pincers some minute
objects that his eyes enable him to see, but which we cannot make out
without a lens. In the securing of larger masses of food the heavy
“hands” would be employed, but to convey small particles of the mass
to the mouth the smaller hands are brought into requisition, and very
daintily they perform their work.
The Prawn resembles the crab in his bold, fearless spirit, and it is
of little moment to him how he comes by his food. In the rock-pools,
as in the aquarium, I have seen him pull some tit-bit out from the
depths of an anemone’s mouth without the slightest ceremony. He does
not quarrel--not a bit. He just walks up to the anemone, and keeping
his body clear of her tentacles by means of his spindly walking legs,
reaches to her mouth with his widely extended pincers--the larger pair.
There is such a matter-of-fact, business-like air about his action that
you would scarcely be surprised if you heard him say, “Hallo! what have
we got for dinner to-day? Young goby, eh! Thanks; I’ll take a little!”
and you see the luckless goby that has been stung by the anemone
quickly withdrawn from her throat and taken off to the Prawn’s den
beneath the big stone at the other end of the pool. In all probability,
if he has happened to arrive just too late, when the anemone’s meal has
entirely disappeared from sight, you will see him giving a sly tweak to
her tentacles.
The young ones swarm in the pools, and you have only to disturb the
drapery of weeds that lines the wall to see a number of them come
out into the middle; but the big fellows, of four inches and more in
length, keep close, as a rule, in a hole or under a stone. Oftentimes
a huge stone that cannot be lifted will be found in a pool supported
upon other stones, or kept away from the floor by the concavity of the
bottom. A thin stick introduced beneath that stone and moved from side
to side will cause several splendid specimens to emerge from obscurity.
It now remains for the disturber of their peace to show his activity by
catching them: by no means an easy thing to do.
I have already dealt in the previous chapter with the principle of
construction in the Crustacea, and the intelligent reader can easily
apply the description there to the case of the shrimps here. As in the
crabs and lobsters the eyes, antennæ, and various parts of the mouth
are all modified feet.
[Illustration: THE PRAWN.]
I would strongly advise my readers to catch a full-grown Prawn, kill it
by immersion in fresh cold water, cut the body through at the junction
between the helmet-like carapace and the first plate of the abdomen,
when the entire contents of both head and body can be cleaned out,
and the space filled with white cotton-wool. When thoroughly dry the
two parts may be reunited by a mere touch with Lepage’s Liquid Glue.
It would be well to do this in duplicate, and whilst still fresh to
take one specimen to pieces, and mount the various appendages on a
white card, gumming them down in their natural sequence. Leaving the
pear-shaped eyes where they are, we commence with the first or internal
antennæ, which we shall thus see has its basal joint spread out into
a broad scale which ends in a sharp spine at the side of the second
joint. It is in this basal joint that the Prawn’s organ of hearing is
contained. Spence-Bate and others have investigated this remarkable
organ in various species, and find there is a little chamber with a
slit-like opening, only to be seen when the creature has just shed his
coat of mail, at which time he picks up with his “finger and thumb”
a few minute grains of sand and carefully introduces them into this
auditory chamber, where they mix with some fine hairs or cilia, and
their agitation when acted upon by sound-vibrations transmits sensation
to the nerves. The third joint gives support to two lashes or “horns,”
one of which in this species is branched.
The basal joint of the second antennæ also bears a flattened scale that
is enormous, being three-quarters of an inch in length and a quarter
of an inch in breadth. There is but one lash (_flagellum_) to this
external antenna, and this strong, long organ measures over six inches
in full-grown specimens; that is, one and a half times the extreme
length of the Prawn from the tip of the forbidding rostrum to the
extremity of the tail.
We have mentioned the two pairs of “hands” (_chelæ_), and behind these
are three pairs of long and slender walking feet. Then, further back,
beneath the abdomen, there are five pairs of swimming organs, and to
these in the female the eggs are attached. The tail-fan must not be
forgotten; it is a beautiful and most effective organ. The four plates
of which it is composed are finely fringed with delicate hairs, and
are so hinged that they can be partially closed one over the other,
or fully expanded to have greater power when opposed to the water.
It is by means of this valuable organ that the Prawn takes those
astonishingly rapid backward leaps which make him hard to be caught
either by man or smaller enemies.
Before leaving the Prawn, I would like to say that our portrait of
him does not pretend to show the length of his antennæ; and it would
be well to make clear how he carries so many to be useful to him. He
is always waving these about, and there can be little doubt that he
receives impressions through their agency, olfactory and otherwise. It
does not matter how far away a Prawn may be; if you give an anemone a
small portion of food, and there is a Prawn at the far end of the tank
he will know it, and will come prancing up to the right neighbourhood.
But his olfactory sense though it helps him to this extent, appears
to act best at a little distance from the fragrant object. I have
frequently observed a Prawn come quickly to the _locality_ where food
has been introduced and evince great excitement and interest; but his
sense has not been fine enough to tell him at once the particular spot
in the locality where it lay. I have on such occasions seen him walk
over what he was seeking, whilst his hands were nervously scraping the
ground and casting around for the delicacy he knew was close by. Now
this is the order of his antennæ-bearing: of the first or internal
antennæ that lash which has the short branch is carried half erect
pointing outwardly, the companion lash pointing forwards, so that he
cannot run against any obstruction without knowing it. The second or
external antennæ are borne with a slight curve forward, then far abroad
on either side. He is thus fairly guarded by sensitive organs well-nigh
all round.
There are two other British species of _Leander_--_L. squilla_ and _L.
fabricii_--which occur in the rock-pools, and may easily be mistaken
for young specimens of _L. serratus_. The distinguishing feature is to
be found in that awe-inspiring, saw-edged rostrum that projects far in
advance of the Prawn’s head, and of which no one has yet discovered
the purpose. In the _bona fide_ Prawn this has a very decided curve
upwards all the way, and on its upper edge it has seven sharp spines
closely following each other, with an eighth lagging a sixth of an
inch behind the seventh, and really on the carapace, not the rostrum;
on the underside there are four close together in the middle, and a
half-hearted one midway between the first of these and the tip of the
rostrum. So much for the type; now for _L. squilla_. The rostrum is
almost straight with a slight upward curve towards its tip. Like its
big relative it has seven or eight teeth above, but _two_ of these
are really part of the carapace, and there are only _three_ spines
below. The second pincer-legs are not proportionately as robust as in
the Prawn, and the creature does not attain to more than half the
Prawn’s dimensions. _L. fabricii_ has the rostrum nearly straight,
with five teeth above and three beneath; in addition, this species has
the rostrum covered with a multitude of minute reddish dots. There are
similar dots in the Prawn, but none in _L. squilla_, with which it
agrees more closely in size. These two, with young specimens of _L.
serratus_, get mixed up and sold together under the name of Red Shrimps
or Cup Shrimps.
There is a somewhat similar form called the Æsop Prawn (_Pandalus
montagui_). It may be distinguished by the fact that the carapace is
distinctly keeled along the foremost half of its upper part, and this
keel is continued forward as the rostrum, which is armed above with
moveable spines, while below it has five fixed teeth. The outer antennæ
are long, and marked throughout by alternate light and dark bands.
The inner antennæ have two lashes, the outer of the two thicker than
its fellow. The first pair of legs are _not_ furnished with nippers;
and the second pair are very unequal in length and stoutness. It is
reddish-grey in colour, dotted with a darker tint. Its length on our
shores, according to Bell, does not exceed two and a half inches; but
on the coasts of the United States it is said to attain to a length of
four or five inches.
There is a beautiful little Crustacean, which may fitly be named the
Varying Prawn (_Hippolyte varians_); it swarms in certain rock-pools
and among the rocks at low-water. In such situations it is not so
widely distributed as some of the species we have named, but it is
worth looking for on account of its remarkable sensitiveness to the
colour of its surroundings. Specimens taken from a pool in which the
green _Ulva_ or _Enteromorpha_ is the prevailing vegetation are green;
but if transferred to a vessel containing only brown, red, or yellow
weeds, will in the course of a few hours be found to have changed their
colours to harmonise with their new environment. So complete is this
change that one can well understand how this shrimp may be commonly
distributed all round our coasts, and yet only known from a few
localities, because a careless observer would never see it. Like the
species of _Leander_ this has a rostrum--in this case quite straight, a
sharp point. On the upper edge there are usually four teeth, but this
number may be increased to five or even six; on the underside they
never exceed two, and there may be only one.
[Illustration: COMMON SHRIMP.]
Whilst referring to these little-known species of Prawns, we must not
forget to mention the very well-known Common Shrimp or _the_ Shrimp
(_Crangon vulgaris_), which affects sandy shores and rivers rather than
rocky coasts. The natural colour of the Shrimp before it has been in
the pot and made to reappear as the _Brown_ Shrimp, is a pale brownish
grey, thickly dotted with darker brown, which harmonises well with the
sandy flats on which it loves to live. Looking at this species we see
how great a finish is given to the Prawns by the possession of that
saw-edged rostrum. By comparison the Shrimp has a square front, which
is by no means so prepossessing. His eyes are not so distant one from
the other as are those of the Prawn, and only one pair of his antennæ
(the external) are at all long. There are three small spines on the
carapace, one on the middle line and one on each side. The first pair
of legs are stout, and what is technically described as _sub-chelate_,
those of the Prawn’s being _chelate_. The Shrimp’s nippers have not
got the well-formed moveable finger and fixed thumb of the Prawn, but
a moveable finger and a little stump upon which it folds down. I do
not pretend that it is not as efficient for the Shrimp’s use as the
better-looking contrivance of the Prawn. The plates of the tail-fan,
too, are narrower than those of the Prawn, but the swimming feet are
longer.
Now these two things would lead us to suppose that the Shrimp depends
less on jumping back from danger than on swimming, and this is true.
If the Shrimp suspects harm he sinks upon the sand, and setting his
swimming feet rapidly to work they “kick up such a dust” in the water
that he is hidden in a cloud of fine sand, which as quickly settles
down and partially buries him--sufficiently so with his sandy hue to
effectually hide him. Upon those swimming feet the female carries her
eggs. From the fact that shrimps may be found laden with these eggs at
almost all seasons, it would appear that they have no special breeding
time; and this fact probably accounts for the endless supply of them.
In common with most other small Crustacea they are constantly preyed
upon by fishes, and we know something of the enormous mortality among
them caused by man, when we think of the heaps in the fishmongers’
shops and in the baskets of the itinerant vendors in towns. But the
united efforts of man and fish do not appear to make them at all scarce.
There are quite a multitude of distinct species of British shrimps, but
many of them keep away from the shore and are only caught in the dredge
or the trawl. Some others swarm after the bait in lobster pots, though
the lobster catcher does not want them, and does not even dignify them
with a name--scarcely notices their existence, in fact. There remain,
however, several species to which I must call attention, even though
my readers may have expected me to have exhausted the list long before
this.
The Chameleon Shrimp (_Mysis flexuosus_) will be found in summer to
abound around the rocks and in the pools. It partakes somewhat of
the character of _Hippolyte varians_ in respect of colouring. If you
take it around rocks that are covered with the _Laminaria_ it is pale
brown, or darker if from among _Fuci_, and in the pools where _Ulva_,
_Enteromorpha_, and _Cladophora_ prevail, its colour will be a light
or dark green. It is a singular-looking shrimp on account of its long
and slender carapace and the cylindrical abdomen. It has six pairs
of feet, and not one among them all possesses a pair of pincers. The
external antennæ are very long, and each is accompanied by a long flat
scale similar to that of the Prawn’s. The eyes are large and very
prominent. The carapace is inclined to have a rostrum, but it is a poor
attempt, and does not extend to more than a third of the eye-stalk. It
is sometimes called Opossum Shrimp, because it has a peculiar pouch in
which the eggs are retained until hatched, and where the young pass
their early days.
There remain several species which should more fitly be included with
the Lobsters, but from their small size they may pass muster with the
Shrimps. They are exceedingly interesting, even if we take but one fact
into account: their habit of burrowing in deep sand like mole-crickets.
Right back in the early days of the present century an enthusiastic
naturalist, Colonel Montagu, was digging for Razor-shells (_Solen_) in
a sandbank near Kingsbridge in Devonshire, when he had the good fortune
to turn up some things he was neither looking for nor suspecting the
existence of--as a matter of fact they were quite unknown until Montagu
unearthed them. Now here is encouragement for anybody and everybody who
turns over weeds, pries into rock-pools and crannies, or digs in the
sand for Launce or Razor-shells. You may or may not find what you seek,
but something of interest you cannot help finding, and it may be a new
fact--if not a new species.
When Montagu published a description of his find in 1808--three years
afterwards--it was under the three-barrelled name of _Cancer Astacus
subterraneus_; but Dr. Leach, six years later, saw that it could not
go into the same genus with the crabs or lobsters, and he called
it _Callianassa subterranea_, by which name it has been known ever
since. So far the account is plain sailing enough, but to attempt a
description of _Callianassa_ is not nearly so simple. The carapace
is very small, with the slightest pretence to a rostrum, flattened
at the sides, rounded above. The eyes very small, like those of its
fellow-digger the mole, though more exposed than his. There are two
pairs of antennæ; the internal ones double. The first legs are adorned
with nippers, but they are very unequal in size, one being scarcely
larger than the second or third feet, and the other much larger than
the carapace, broad, flat, and hairy on the edges. On the outer side of
the arm of this big limb there is a process which looks like a reaping
hook. Now, the word _Callianassa_, I presume, is made up from two Greek
words (Kalli, anassa), signifying Beautiful Queen; but I fancy that
if a female monarch had one of her hands normal and the other bigger
than her chest and head combined, none but courtiers would flatter
her by declaring she was beautiful, and possibly they might be partly
actuated thereby through a wholesome fear of that big hand. However,
she is beautiful in respect of colouring--a fine bright pink, which
departs with life. The second pair of legs are small and terminate in a
little pair of pincers; the third have one finger which works against
the enlarged next joint; the fourth terminate simply in a claw; the
fifth in an intermediate condition as though the extremities intended
to develop into pincers. The seven-jointed abdomen is long, the fifth
segment broadest, from which it narrows gradually to the front, and
suddenly to the rear, where it is finished off with a tail-fan of four
plates. From a glance at the Beautiful Queen’s hands and with knowledge
of her burrowing habits, I should suppose that the bigger of the two
served the double purpose of a digger and a street-door; the latter
to keep enemies and prying intruders out of her burrow. Her majesty
measures about two inches in length, and her crust is very thin and
parchmenty.
That was a day to be remembered by Colonel Montagu, for on the same
occasion he unearthed another burrower--_Upogebia stellata_--new to
science. This is more lobster-like than Callianassa in form, though
less so in size, for it is only about an inch and a half in length. It
is content with having pincers to the first pair of legs, and these are
nearly equal in size. All the limbs are liberally fringed with long
hairs. The carapace begins with a small and sharp rostrum. Dr. Leach
records it from mud in Plymouth Sound. Its colour is yellowish-white,
sprinkled with minute orange spots.
And now, though we have by no means exhausted the list of British
species, we must close this chapter. It should be stated that all these
creatures go through a series of transformations similar to, but not
identical with, those marking the early life of the crab and lobster.