A Year at the Shore

by Philip Henry Gosse

FOOD-GATHERING ORGANS.

The organs which he employs for this end are the outer foot-jaws or pedipalps, which are of unusual length, and are fringed with incurving hairs. Watching a Flat-crab beneath a stone close to the side of my tank, I noticed that his long antennæ were continually flirted about; these are doubtless sensitive organs of touch, or some analogous sense, which inform the animal of the presence, and perhaps of the nature, of objects within reach. At the same time I remarked that the outer foot-jaws were employed alternately in making casts; being thrown out deliberately, but without intermission, and drawn in, exactly in the manner of the fringed hand of a barnacle, of which both the organ and the action strongly reminded me. I looked at this more closely with the aid of a lens; each foot-jaw formed a perfect spoon of hairs, which at every cast expanded, and partly closed. That this may be better understood, I may say that the foot-jaw resembles a sickle in form, being composed of five joints, of which the last four are curved like the blade of that implement. Each of these joints is set along its inner edge with a row of parallel bristles, of which those of the last joint arch out in a semicircle, continuing the curve of the limb; the rest of the bristles are curved parallel or concentrical with these, but diminish in length as they recede downwards. It will be seen, therefore, that when the joints of the foot-jaw are thrown out, approaching to a straight line, the curved hairs are made to diverge; but as the cast is made, they resume their parallelism, and sweep-in, as with a net, the atoms of the embraced water. The microscope revealed to me a still higher perfection in this admirable contrivance. I then saw that every individual bristle is set on each side with a row of short stiff hairs, projecting nearly at right angles to its length; these hairs meeting point to point those of the next bristle, and so on in succession, there is formed a most complete net of regular meshes, which must enclose and capture every tiny insect or animalcule that floats within its range; while, at each out-cast, it opens at every mesh, and allows all refuse to be washed away or fall to the ground. For we are not to suppose that the captures thus promiscuously made are as indiscriminately swallowed. A multitude of atoms are gathered, which would be quite unfit for food; and a power of selection resides in the mouth, whether it be the sense of taste or touch; or any other analogous but recondite perception, by which the useful only is admitted, the worthless, or at least the injurious, being rejected.

SQUAT-LOBSTERS.

Companions of the Flat-crabs, closely allied to them in all essentials of form and structure, yet widely separated by general figure and appearance, and to some extent by habits too, are the Squat-lobsters. They, too, are somewhat flat, but they are more decidedly lobster-like, with a distinctly jointed abdomen as broad as the body, terminating in wide and strong swimming-plates. This portion is, during rest, thrown-in under the body, much more completely than a true lobster or prawn can do it, and yet is by no means so permanently set in that position as in the true crabs. The Flat-crabs and the Squat-lobsters constitute an intermediate group between the short-tailed and the long-tailed Crustacea, the Flat-crabs inclining to the one, the Squats to the other alliance. When the abdomen is wrapped-in, the outline of the Squat is nearly oval, particularly in the commonest species, the Olive or Scaly Squat.[94] That of the Scarlet or Embleton’s species[95] is a longer ellipse. The front runs out into several sharp spines, as do also the edges of the carapace; and the inner edges of the front limbs, which carry long and stout claws, are very spiny. More formidably armed in this respect, however, than either, is another species, found occasionally at low-water, the Painted or Spinous Squat,[96] all the limbs being set, on both edges, with stout sharp prickles. The last named is the largest kind, being sometimes four inches long; then the Olive, which is commonly from two to two and a half; while the Scarlet rarely exceeds an inch and a half. They differ very much in colour, the Olive being of a dull blackish green, with narrow transverse lines of pale yellowish; the Painted somewhat of the same general hue, but with the eyes and the tips of the claws of the most vivid scarlet, while the body is varied with lines and spots of an equally brilliant azure. Embleton’s is of a more or less bright red, varying from a light orange or warm cream colour to a full orange, clouded with patches of deep scarlet. The last is an inhabitant of deep water, obtained only by the dredge; by this means, however, I obtain it in considerable numbers. The other two are found, the first abundantly, the second rather rarely, under stones in our coves. I have found, in autumn, in such situations, several specimens of small size, rather smaller than full-grown Embletons, which I conclude to be the young of the Painted. The whole body is pale blue, tesselated all over with black and reddish brown; the legs are banded with red, and the hands are of the same colour. They have a very pretty appearance.

The whole race are very cautious and timid. With the long claws, and the longer antennæ, stretched out to their utmost in front, the suspicious Squat feels the unknown ground with delicate touches; should he touch any object that moves, he gives on the instant a vigorous flap with the broad incurved tail, and shoots backward through the water to the distance of several inches. At the same moment all the legs are thrown forward in the line of the body, to diminish the resistance. Mr. Couch says: “It is very remarkable to witness the accuracy with which they” [he is speaking of the Painted species specially] “will dart backward for several feet into a hole very little larger than themselves: this I have often seen them do, and always with precision.” This would surely be a remarkable feat for an animal in the air; how much more through a medium so dense and resisting as sea-water!

I have elsewhere[97] described and figured the young of a species of this genus in two of its stages. In the first it may be compared with a prawn, having a lengthened slender body, whose fore part is protected by a prawn-like transparent carapace, with an immensely long straight spine in front, and two hooked ones behind. In the next stage the general figure is acquired, but still the form is more like that of Porcellana than of Galathea.

VIII.
AUGUST.

What eager pursuer of marine animals has not gloated over a rock-pool? On all our rocky coasts we find them more or less developed; but it is on these south-western shores, where the compact limestone juts out into promontories, that we find them in perfection. The burrowing mollusca specially favour the limestone; the Saxicava, I think, lives in no other medium; and it is to the operation of this coarse ugly little shell-fish that this rock is indebted for the honeycomb-like excavation which has eroded its surface. Below a few inches this erosion does not extend, for the Saxicava is but a small animal, and its siphons must reach the orifice of its burrow; therefore it never goes deeper into the stone than will allow it comfortably to bathe its red nose in the free water, though it is not at all particular about the angle to the surface at which it bores. The myriads and myriads of these auger-holes that have been bored remain, though the feeble animals perish generation after generation; each new-born shell-fish makes a new bore for itself, never appropriating one ready-made, and so there is a perpetual excavation of the living rock with these shallow auger-holes, always of the same width, or nearly; about half-an-inch. The result is what we see; that the surface of the rock knows no such thing as a plane surface, but a surface covered with smooth borings, running in all directions, so as continually to break in on one another; and that so close together, that the interspaces form narrow knife-edges, and sharp angles and projecting points. A particularly interesting circumstance is, that this honeycombed condition is characteristic not only of that level of the rock which is covered by the sea for some portion of every tide, but of that part, to a certain height, which is never covered at all. The Mollusca, it is true, cannot live wholly deprived of sea-water, and, in fact, there are none in this ever-dry portion, though the burrows by thousands testify that they were there once. We must infer that the coast has been generally elevated; perhaps by slow and imperceptible degrees, by an operation still proceeding but unappreciated; perhaps by some sudden convulsion which took place at a remote era, unrecorded and forgotten.

HOW ARE ROCK-POOLS MADE?