Page:American Seashells (1954).djvu/66

48 When it is darting rapidly, the lobes of the caudal fin are closely wrapped around the body, and the arms are held tightly together to form a streamlined outline. Except when attacking or escaping, the squid swims less strenuously, using the caudal fin as a balancing organ.

There are few sights as interesting as that of squid engaged in capturing and devouring young mackerel. During the summer this chase may be observed from certain wharves in New England. In attacking mackerel the squid darts backward among the fish with the velocity of an arrow, and then turns obliquely to one side and seizes a fish, which is almost instantly killed by a bite in the back of the neck by the squid’s sharp beak. The bite is always made in the same place, cutting out a triangular piece of flesh, and is deep enough to penetrate to the spinal cord. The attacks are not always successful and may be repeated a dozen times before one of the wary fish can be caught. Between attacks a squid may suddenly drop to the bottom and, resting on the sand, change its color to that of the sand so perfectly as to be almost invisible. Ordinarily, when swimming, it is thickly spotted with red and brown but, when darting among the mackerel, it appears translucent and pale. The schools of young mackerel often move close to shore where the water is shallow and offers more protection. In their eagerness to capture fish, the squid frequently force themselves up on the beach where they perish by the hundreds. At such times they often discharge their ink in large quantities.

Many species of octopuses and squid possess an ink sac and, in moments of great excitation they may expel a large cloud of black or brown liquid through the siphon. The ink is of a caustic nature and, in addition to its use as a “smoke screen,” it is believed to be distasteful to hungry fish. Two sources of sepia ink are a species of squid found along the southeastern coast of China and another found in the Mediterranean Sea.

Many geologic eras ago the cephalopods possessed large and showy shells. Today, however, shells produced by this class are a rarity. The most spectacular shell is found produced by the Indo-Pacific Chambered Nautilus, Nautilis pompilius. On our shores, the small, white, spirally coiled shell of Spirula is frequently encountered on southern beaches. The three-inch-long Spirula squid which produces this shell is a denizen of deep water. In other squid the internal shell has been reduced to a simple slab of chalky material (the cuttlefish bone fed to canaries) or, in the case of the Loligo squid, to a thin, elongate shaft of transparent, horny material.

By an odd turn of fate, squid are heavily preyed upon by adult cod, mackerel and other fish, and no doubt some young mackerel which have escaped by a tentacle’s breadth have lived to devour later their would-be assassins. Squid are taken in large quantities in nets and weirs each year, and they constitute one of the main fish baits on the Grand Banks. They are