Many of these animals have a powerful tail, consisting of a certain number of ciliated paddles, which it uses in swimming to beat the water, and to confuse its enemies.
The Crustaceans, so far as they are aquatic, respire by means of branchiæ, or gills. In the larger species these branchiæ are lamellous, or with filaments, whose supports are traversed by two canals, one of which leads the blood into the general economy, the other directs it towards the heart. These organs are enclosed in the body. In the smaller species the branchiæ often appear exteriorly, hanging in the water like a fungus. Sometimes these are at once swimming and breathing organs; in other cases the animal has no special organs of respiration.
Nearly all the Crustaceans are strong, hardy, and destructive, forming a horde of nocturnal brigands—merciless marauders, who recoil from no trap in which they can lie in wait for their prey. They fight à l'outrance not only with their enemies, but often among themselves, either for a prey or for a female, sometimes for the sake of the fight. The miserable creatures struggle audaciously with their claws. The carapace generally resists the most formidable blows; but the feet, the tail, and, above all, the antennæ, suffer frightful mutilation. Happily for the vanquished, the mutilated members sprout again after a few weeks of repose. This is the reason for the many Crustaceans met with having the talons of very unequal size: the smaller are those lost in battle replaced. Nature has willed that the Crustacean should not long remain an invalid. They soon return cured of their wounds. "We have seen lobsters," says Moquin-Tandon, "which have in an unfortunate rencounter lost a limb, sick and debilitated, reappear at the end of a few months with a perfect limb, vigorous, and ready for service. O Nature, how thou fillest our souls with astonishment and wonder!"
On the Spanish coast there is a species of crab, known, singularly enough, by the name of Boccaccio; it is caught for its claw, which is considered excellent eating. This is cut off, and the mutilated animal is thrown into the sea, to be taken at some future time when the claw has reappeared.
Crustaceans are nearly all carnivorous, and eat eagerly all other animals, whether living or dead, fresh or decomposed. Little think they of the quality or condition of their food. It is amusing to witness the address and gravity with which the common crab, when it has seized an unfortunate mussel, holds the valve open with one claw, while with the other it rapidly detaches the animal, carrying each morsel to the mouth, as one might do with the hand, until the shell is entirely empty. The crab does not kill its prey directly, like the lobster; it is swallowed also, but with greater appreciation.
M. Charles Lespés surprised upon the shore at Royan a shoal of crabs at their repast. This day they seem to have dined in common, and "God knows the enjoyment," as the good Fontaines said. They were in rows, every head turned to the same side, and nearly on end on their eight feet. They seized the small objects on the shore, which were carried to the mouth, each hand in its turn in regular order: when the right hand reached the mouth the left was on the ground. Let us just figure to oneself a company of disciplined soldiers messing together at the same table!
The Long-horned Corophius (Corophium longicorne), remarkable for its long antennæ, knows perfectly well how to cut the byssus by which the mussels suspend themselves, in order that the bivalve may fall on the weeds among them. Other Crustaceans, also great oyster-eaters, have the cunning or instinct to attack the mollusc without exposing themselves to danger. When the bivalve half opens its shell to enjoy the rays of the sun or take food, the evil-disposed Crustacean slips a stone between the valve. This done, it devours the poor inhabitant of the shell at its leisure.
The Corophius, respecting whom this question is hazarded, are extremely numerous on the shores of the Atlantic towards the end of summer and autumn. They make constant war upon certain marine worms. Off the coast of La Rochelle they may be seen in myriads beating the muddy bottom with their long antennæ in search of their prey. Sometimes they meet one of these Nereida or Arenicola many times their own size, when they unite in a body to attack it. In the oyster beds of La Rochelle they are useful friends to the oyster by destroying these enemies, although they do not hesitate to attack the mollusc when it comes in their way. During the winter the mud of the bouchots gets piled up in unequal heaps, and when the warm season returns, it has become hard and unfit for the cultivation of the mollusc. It is necessary to level and dry these mud-heaps—a process which would be both difficult and costly. Well, the Corophia charge themselves with the task. They plough up annually many square leagues covered with these heaps. They dilute the mud, which is carried out by the ebbing tide, and the surface of the bay is left smooth, as it was in the preceding autumn.
We have said that the Crustaceans do not even respect each other; the larger of the same species often devour the smaller. Rara concordia fratrum! Mr. Rymer Jones relates that he had on one occasion introduced six crabs (Platycarcinus pagurus) of different size into an aquarium. One of them, venturing towards the middle of the reservoir, was immediately accosted by another a little larger, which took it with its claws as it might have taken a biscuit, and set about breaking its shell, and so found a way to its flesh. It dug its crooked claws into it with voluptuous enjoyment, appearing to pay no attention to the anger and jealousy of another of its companions, which was still stronger and as cruel, and advanced towards them. But, as Horace says—and he was not the first to say it—"No one is altogether happy in this lower world":
"Nihil est ab omni parte beatum."