NAUTILUS, DEVILFISH, AND SQUID
We have now arrived at the last and highest division of the Mollusca—the Cephalopoda, the class of the nautilus, ammonite, and other fossil forms, and of the squid, cuttles, and octopuses of our modern seas. The cephalopods are very different in shape, activity, and in their higher organization and intelligence, from other mollusks, but their general anatomy is the same. The special characteristic, as indicated by the name, is the fact that the head is surrounded by tentaclelike extensions of the "foot," which is here fused in part with the head, and divided into the long "foot arms," which are the instruments by which these predatory creatures obtain their prey. The underpart of the foot forms a tube called the funnel (or siphon). Through the funnel the animal expels water from the mantle cavity, and thus propels itself through the water. When the siphon is in its normal position the animal swims backward; but it can be turned back over the edge of the mantle, giving a forward movement. In cephalopods the sexes are separate, the male being often much smaller than the female. The eggs are usually laid in gelatinous capsules, commonly known in New England as "sea grapes," and the development is direct, that is, without any free-swimming larval stage.
The class is divided into two subclasses: 1. Tetrabranchiata, cephalopods with four plumelike gills inside the mantle; and 2. Dibranchiata, with only two such gills. In the first subclass belong all those very ancient cephalopods called in a general way ammonites, goniatites, orthoceratites, etc., that are found in such great numbers and astonishing variety in the Paleozoic rocks, from the Ordovician age onward, although but few groups survived beyond the Carboniferous period, and only two families can be traced as high as the Tertiary deposits, one of which—that of the nautilus—survives to the present day as the final remnant of one of the conspicuous and interesting populations of the primitive ocean.
The pearly or chambered nautilus is one of several species inhabiting the East Indies and the coral region of the South Pacific seas, creeping along the bottom in deep water, most numerously at the depth of about 1,000 feet. Hence the animal is not often taken alive, although the smoothly coiled and handsome shells are cast on the beaches in great numbers; and little is known of its habits or embryology. It is a soft lumpish sort of creature, with a great number of short arms and tentacles around the mouth, none armed with suckers. It begins life as a mere globule covered by a minute hood of shell; but presently, growing too large for this hood, it enlarges it by additions to the rim, and then forms behind its body a partition (septum) across the shell, cutting off the part in which it was born. As growth advances, this enlarging and partitioning continues until the nautilus has attained its full size. Then, as before, it occupies only the outermost chamber, behind which the whole interior of the shell is divided by the septa into chambers, abandoned and empty, but filled with a gas that buoys it up in the water. Oriental artists are fond of grinding away the dull exterior of the shell and exposing the gleaming nacre underneath; and of carving in this mother-of-pearl picturesque designs, examples of which are often to be seen in curiosity shops. This is not only the last remnant of the great group of ancient nautiloids, but one of the smallest, for some of the Paleozoic coiled forms were as big as a washtub, and the straight ones were often six feet long.
The Dibranchiata, on the other hand, are comparatively modern, as their ancestry dates back only to the Trias, and our seas still harbor a long list of living representatives. This subclass has two divisions: 1. Octopoda—octopods, the eightarmed argonaut and other octopuses; and 2. Decapoda—decapods, the ten-armed cuttlefishes, or calamaries, and the squids.
| THE CHAMBERED NAUTILUS—SECTION |
| H, Head. T, Tentacles. E, Eye. M, Muscles. S, Shell. A, Air Chambers |
The octopods have a saclike body with eight arms of about equal size, in some kinds thick and short, in others long and snaky. Every arm has along its underside a double row of round, muscular suckers without horny rims; and whatever is seized by one or more of these arms is drawn into the mouth at their base, where it is bitten by a beaklike jaw of sharp horn, and further devoured by means of a toothed tongue similar to the radula of gastropods. Nearly all are tropical, but some species exist in deep water considerably to the northward. Certain species are used as food in many parts of the world, and are considered a delicacy in Italy and other Mediterranean countries. The fishermen of Japan and the Philippines capture them by the simple process of lowering big earthen urns and leaving them on the bottom overnight; when they are hauled up in the morning many will contain entrapped devilfish, as sailors call them, which at once go to market.
A very singular octopod is the little argonaut, or "paper sailor." Its body is not larger than a walnut—that is the body of the female, for the male is only a tenth of that bigness. Its home is mainly in the tropics and in deep water, but in the summer spawning season it rises to the surface, and is occasionally met with far northward on the Gulf Stream, drifting, apparently, in a snug little boat. The two dorsal arms are expanded into broad, roundish membranes at their ends, and old stories said that they were used as sails—a supposition of much use to poets; but the "boat," shaped somewhat like the shell of the nautilus, is not a shell proper, but a membranous pouch secreted by the mantle in spawning time, and not vitally attached to the body, but held in place beneath it by the two broadened arms, and serving as a receptacle for eggs and a cradle for the embryos hatching from them.
Turning now to the Decapoda, we treat of things much nearer home and familiar on both sides of the continent, for these are the cuttlefish and squids, none of which have an external shell, but possess an interior brace to their muscles either of lime or of chitin. The cuttlefish proper, or calamaries, are those of the family Sepiadæ, which have an oval, flattened body bordered by a fin; and two of the ten arms are, in the female, in the form of long, slender tentacles. In addition to being edible and easy to get, as they stay near shore, their calcareous back brace is the "cuttlebone" fed to cage birds; and they furnish the substance from which the drawing ink called "sepia" is made—principally in Rome. This is a brownish black liquid that the animal jets out through its siphon when it thinks itself in danger in order to make an inky cloud in the water behind which, as a sort of smoke screen, it may run and hide. Other cephalopods use this means of escape.
The squids, however, are all elongated in shape, and have finlike expansions of the mantle only on the tail. Two of their arms are long and slender, and are broadened at the tips, and studded with suckers. These suckers in some squids are strengthened by a horny rim, or by recurved hooks, or by both. The eyes are large, perfectly formed, and as serviceable as those of the fishes on which they prey. These, and some other animals, including small ones of their own kind, they capture by darting backward, swinging quickly to one side and seizing the victim in their sucker-bearing arms. They themselves are devoured by whales, seals, and many kinds of fishes; and enormous quantities of squids of various species are annually collected by fishermen for use as bait in the Newfoundland fisheries. In place of the calcareous cuttlebone of the sepia the squids have their bodies stiffened by an internal strip of chitinous substance called the "pen."
Squids are of all sizes from an inch to twelve feet in length; then there is a surprising jump to the giants (Architeuthis) of the North Atlantic, which, when the tentacles are stretched out in front, may measure seventy-five feet from tip to tail. These are little different in structure or habits from their smaller brethren that exist in so many species near all coasts and throughout the midseas right around the globe; but their huge size makes them fit antagonists of the sperm whale, which hunts them, and whose hide often bears a record, left by their powerful suckers, to show how hardly some big squid struggled for life. These monsters are the greatest invertebrates known in present or past time; and it is probable that the long wriggling arms of one and another, glimpsed at the surface, may account for some of the sea serpent stories brought home by apparently perfectly honest sailors, especially those which in many cases recount that the supposed "serpent" was in conflict with a whale. Carcasses of these gigantic squids are occasionally cast on the shores of Labrador and Greenland.
[CHAPTER X]
ANIMALS WITH JOINTED FRAMES
The phylum Arthropoda embraces an immense assemblage of small animals, inhabiting salt and fresh waters, the land, and the air above it. The typical members of this group have a body divided into segments, jointed limbs, some of which are modified into jaws, and a more or less firm external skeleton. The general organization is complex, with the nervous system and senses well developed, in some divisions showing powers of perception and brainwork of a very high order. The chief divisions, or classes, of the Arthropoda are given below in the order of rank, from those simplest in organization to the most complex. Members of the first three classes breathe by gills, and are termed Branchiata, the remainder are air breathers or Tracheata.
Crustacea—Crabs, lobsters, shrimps, barnacles, beach fleas.
Trilobita—Trilobites; eurypterids (fossil only).
Xiphosura—Horseshoe crabs.
Onychophora—Peripatus.
Myriapoda—Centipedes; millipedes.
Arachnoidea—Spiders, mites, ticks, scorpions.
Insecta—Insects.
As several of these classes contain many subdivisions, and thousands or even tens of thousands of species, all that is possible is to give the reader such an account of each important group, as will enable him to assign to their proper place such arthropods as he may encounter in his rambles, or in his reading, and to learn something of the manner of life in the various groups.