CHAPTER XI.
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.
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.