SOME MINOR CRUSTACEANS.
Besides the crabs and shrimps already enumerated there are to be found
upon our shores a great variety of smaller species of Crustacea,
representing widely differing tribes and orders. We cannot fill a phial
with water from a rock-pool without getting a number of specimens
of the crystal-cased water-fleas (_Entomostraca_), of which we are
probably already acquainted through several well-known fresh-water
forms. We cannot pull up a tuft of fine weed from the same pool but
we shall find on putting it into a tumbler of water that it harbours
a multitude of Crustaceans much larger than the water-fleas; and so
when we place in our aquarium a rough bit of rock, because it is the
resting-place of a tube-worm, an acorn-shell, or a patch of polyzoa, we
shall find it is also occupied by little shrimp-like, or woodlouse-like
creatures. There is every probability, too, that we shall get with
these the minute larval forms of crabs and lobsters. It is a delight
to introduce them in this way, and to be constantly making the
acquaintance of unsuspected inmates of an aquarium that perhaps only
holds a couple of quarts of water.
Of course, there is no difficulty in collecting these smaller species
of set purpose, any more than there is in looking for anemones and
sponges; but whether the shore-naturalist seeks them or not, he is
bound to get a large variety.
The majority of these will be species of the two important sub-orders,
Isopoda and Amphipoda, and one of the most conspicuous, because
largest, of them is the Sea Slater (_Ligia oceanica_), represented in
our next illustration. It will be found crawling up the perpendicular
faces of rocks about half-tide mark; and the finder will not need to
have explained to him the fact that it is related to the terrestrial
Woodlouse or Slater of our hedgebanks. The whole tribe have the
respiratory apparatus adapted for breathing air, but they appear to
require a damp atmosphere.
[Illustration: SEA SLATER.]
Among the fringing weeds of the rocks there will be found great numbers
of a lively creature of somewhat similar build to the _Ligia_, but very
narrow (oblong-ovate is the technical description), and without the
terminal appendages (_uropods_) of that creature. It varies in colour
from pale brown to a dark brown, perhaps mottled with black. There are
several British species, but the common shore-haunting kind is _Idotea
marina_. Its great variation has caused it to be called by at least a
dozen names.
In turning over any organic remains above the reach of the waves,
we shall uncover swarms of the Shore-hopper (_Orchestia littorea_),
distinguished from the similar Sand-hopper (_Talitrus locusta_) by its
more compressed body, and by having both the first and second pairs of
feet clawed, whereas in _Talitrus_ the second pair are not clawed.
Among the dried up, black-looking foliage of _Lichina pygmæa_,
which grows on the rocks that are covered only for a short time at
high-water, will be found the queer Isopod, _Campecopea hirsuta_, which
seems to mimic the plant that shelters it. They curl up tightly into a
ball, and roll about if dislodged. The projections at the end of the
body (_uropods_) help their resemblance to the _Lichina_. This species
must not be confounded with the similar and allied _Næsa bidentata_,
which has the sixth segment of the trunk much larger than the others,
and produced backwards in the _two teeth_-like processes, which
suggested its Latin name.
If one is so fortunate as to get access to the rocks at the equinoctial
low tides, which are lower than the ordinary fortnightly “springs,”
he will see rocks covered with a muddy felt, much of which appears
to be the work of marine worms, who live in it. A portion of this
coating should be rapidly prised off with the putty-knife, and put
into a bottle of sea-water by itself. At the same time look for a
dirty-looking slaty rock, at the same level, and take off the upper
flakes, with their investing crust of acorn-shells, corallines,
zoophytes, etc. On this will almost certainly be found the absurd
acrobat or contortionist, the Skeleton-shrimp (_Caprella linearis_),
sprawling about, his walking feet on the extreme segments of an
extremely long and thread-like body. Here will, in all probability,
also be found a Crustacean with a body not more than half an inch
long, but looking much longer by reason of an enormous development of
its outer antennæ, which it flourishes about as though they were long
arms. The chief use it makes of these is as flails to thresh out its
prey, certain marine worms that inhabit the mud-felt to which we have
referred. By repeated heavy beatings on the mud with these antennæ, the
worms are induced to come outside their burrows to see what danger is
threatening them, and find out only too quickly.
The first time I saw this remarkable creature, I was greatly moved
to mirth. I had wrested a flake of rock from a huge mass that was
ordinarily covered at low-water, but which now at the equinox reared
its head high above the waves, and exposed treasures in the shape
of the Globehorn and the Rosy Anemones. _Corynactis_ was growing at
the edge of this flake, which was placed near the glass of a small
aquarium, where it could be easily scanned with a lens. A few hours
later I took a glance at my Globehorns, and was astonished to witness
the activity and vigour of the varied colony that was settled on these
few square inches of stone. Several acorn-shells were in “full swing,”
a tube-worm (_Sabella_) had put out its plumes from the mouth of its
tube, a patch of polyzoa exhibited its crowns of prismatic tentacles,
a couple of _Caprellæ_ were sprawling around in an inebriated fashion,
whilst near one corner was the figure that chiefly attracted my
attention. _Corophium longicorne_ was standing erect in a mud-pulpit,
above the walls of which he was flourishing his arm-like antennæ as
he--a Crustacean St. Anthony--harangued the other members of the
community who appeared to be paying great attention to his discourse.
I felt that if I could but restrain my laughter, I should hear the
“thirdly, my brethren beloved,” and the telling sentence he emphasised
by a hearty smack on the pulpit; the ridiculous _Caprellæ_ profoundly
bowing in assent to his postulates all the time.