Part 22

FLAT-CRABS.

Let us turn from these investigations, fascinating as they are, to examine the ways and means of two or three other creatures, familiar enough to us who habitually explore the sea-margin. I allude to certain members of the great class CRUSTACEA, not Crabs nor Lobsters exactly, but called so by courtesy, something in fact between both. My dredger’s hauls are always sure to contain, creeping in the tangled thickets of Laomedea, Antennularia, and other of the flexible Polyps, or playing at bo-peep from the interstices of the Serpula masses,--numerous specimens of a tiny Crab, with a circular flat shell, no bigger than a split-pea, large wide claws, and very long antennæ, like two hairs. They are of various colours, sometimes pure white, sometimes chocolate-brown, and often clouded with different hues. Minute as they are, they are not despised by great fishes; for the heavy-sided, clumsy-headed cods, that occupy so large an area on the fishmonger’s slab, are often found to have their stomachs packed full with these little Crabs; which doubtless the glutton picks off one by one, enjoying the taste of the savoury atom as it rolls over his fat fleshy tongue.

THEIR MANNERS.

But we may much more easily procure specimens of his bigger brother, the Shaggy Flat-crab, which abounds under nearly every flat stone at low-water on Babbicombe beach, and indeed almost everywhere else, under the like conditions. He is a curious subject, though far from attractive as to his personnel, for he is, I regret to say, of irreclaimably dirty habits. You never find him but he is begrimed and saturated, so to speak, with the impalpable red mud of which our soil consists,--the débris of the red sandstone. Yet blame him not. He is more hirsute than a modern swell; his hands and his face are as hairy as Esau’s; a dense short pile of stiff bristles stands out from all his prominences, and catches and entangles the sediment in the midst of which he loves to riot. I say again, blame him not; we must not infer that he likes dirt for its own sake, because he gets his living in it, any more than the sweep or the dustman chose his trade because he had a penchant for the grime. Nay, dirty as our little flat friend is, he is endowed with organs expressly for the purpose of cleaning himself, and fails not to use them too. On first looking at him you would suppose, comparing him with other Crabs, that he was short of one pair of feet; yet presently, from a narrow, almost invisible crevice behind, he jerks out two jointed limbs, as slender as bristles, which, however, are each terminated by a tiny two-fingered claw, and are beset throughout their length by stiff short hairs standing out at right angles, like a brush. These feeble limbs are indeed cleansing brushes, with which he keeps certain portions of his person clean, applying them with the greatest ease to the whole surface of the abdomen, and under-side of the carapace or body-shell, while the delicate fingers of the little hand are used to pick off adhering matters that cannot be removed by brushing. Then having done his washing, he cleans his brushes with his mouth, and snugly folds them up, and packs them away in their groove till he wants them again. Yet with all this, he remains, as I said at first, a dirty subject notwithstanding.

PLATE 21.

P. H. GOSSE, del. LEIGHTON, BROS.

OLIVE SQUAT-LOBSTER. SHAGGY FLAT-CRAB. SCARLET SQUAT-LOBSTER. ]

A curious chapter in the history of this little creature, which I have put on record elsewhere, is, I think, so very instructive, that I may venture to repeat some parts of it here. Let me premise that the Crab habitually lives under stones, a habit for which the remarkable flatness and thinness of all its parts adapts it; he has somewhat of the appearance of having been crushed flat by the pressure of the stone under which he lives. He does not wander much to seek his food, but expects it to be brought to him, he making provision for its conveyance.

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. That of the Scarlet or Embleton’s species 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, 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 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.

FOOTNOTES:

Lepidogaster bimaculatus, of which individuals of different varieties of colour, and in different attitudes, are represented in Plate XIX.

Let me refer my readers to an excellent and most interesting paper on this little fish, by my friend, Mr. W. R. Hughes, in the Zoologist for July 1864.

Asterina gibbosa, figured in the right-hand foreground of Plate XX.

Echinus miliaris, a specimen of which may be seen delineated in Plate XX., in the upper left-hand corner.

Comatula rosacea; a fine specimen of which, taken by myself in a little cove near Torquay, I have delineated in the centre of Plate XX.

Porcellana longicornis.

Porcellana platycheles, represented by the central figure in Plate XXI.

The Aquarium: 2d Ed. pp. 37-45.

Galathea squamifera, represented in Plate XXI., at the left hand, in the act of shooting backward.

G. nexa, for which see the right-hand corner of the same Plate.

G. strigosa.

Tenby, p. 169, Plates VII. and VIII.

VIII.