The Sea and Its Living Wonders / A Popular Account of the Marvels of the Deep and of the Progress of Martime Discovery from the Earliest Ages to the Present Time

by G. Hartwig

Worm-Shell.

While the vast majority of the gasteropods either creep or swim, some are doomed to the sedentary life of the oyster, and remain for ever fixed to the spot where they first attached themselves as small free-swimming larvæ. Thus the Magilus antiquus, which in its young state presents all the characters of a regular spiral univalve, establishes itself in the excavations of madrepores, and as the coral increases around it, the Magilus is obliged, in order to have its aperture on a level with the surrounding surface, to construct a tube, lengthening with the growth of the coral. As the tube goes on increasing, the animal abandons the spiral for the tubular part of the shell, and in the operation it leaves behind no partitions, but secretes a compact calcareous matter which reaches to the very summit of the spiral part, so that in an old specimen the posterior part of the shell presents a solid mass.

The Siliquariæ are generally found embedded in a similar manner in sponges or other soft bodies, while the Vermetus, or Worm-Shell, usually attaches itself, like the Serpulæ, to rocks, coral-reefs, or shells.

In these genera, which have been arranged by Cuvier in a separate order (Tubulibranchiata), the foot is naturally reduced to the state of an adhesive organ, its chief functions consisting in opening and closing the lid.

The sea-snails are either predaceous or herbivorous; among the pectinibranchiates, those with circular mouths to the shell are vegetable feeders, while such as have an aperture ending in a canal are animal feeders. Considerable modifications of internal structure indicate this difference of food; and the external organs, particularly about the mouth, exhibit a corresponding variety of form. In those which feed on vegetables the mouth is generally a slit furnished with more or less perfect lips, armed with a simple cutting apparatus, which is often powerful enough to divide or dismember comparatively hard substances.

In most animal feeders the mouth presents the appearance of a proboscis that can be protruded or shortened at the will of the animal, and which, grasping the food, conveys it to a spine-armed tongue, by the aid of which it is propelled into the gullet without mastication or any preparatory change.

In the Whelk and its shell-boring allies, the alternate protrusion and retraction of the proboscis, which is here of a much more complicated structure, causes the sharp tongue to act as a rasp or auger, capable of drilling holes into the hardest shells. It is this circumstance which renders the whelk so formidable an enemy to mussel and oyster banks. During the erection of Bell Rock lighthouse, an attempt was made to plant a colony of mussels on the wave-beaten cliff, as they were likely to be of great use to the workmen, and especially to the light keepers, the future inhabitants of the rock; but the mussels were soon observed to open and die in great numbers. "For some time," says Mr. Stevenson in his interesting narrative, "this was ascribed to the effects of the violent surge of the sea, but the Buccinum lapillus having greatly increased, it was ascertained that it had proved a successful enemy to the mussel. The buccinum was observed to perforate a small hole in the shell, and thus to suck out the finer parts of the body of the mussel; the valves of course opened, and the remainder of the shell-fish was washed away by the sea. The perforated hole is generally upon the thinnest part of the shell, and is perfectly circular, of a champhered form, being wider towards the outward side, and so perfectly smooth and regular as to have all the appearance of the most beautiful work of an expert artist. It became a matter extremely desirable to preserve the mussel, and it seemed practicable to extirpate the buccinum. But after we had picked up and destroyed many barrels of them, their extirpation was at length given up as a hopeless task. The mussels were consequently abandoned as their prey; and, in the course of the third year's operations, so successful had the ravages of the buccinum been that not a single member of the imported mussel colony was to be found upon the rock." Thus the engineer, whose skill and perseverance had gained so proud a triumph over the waves of the stormy ocean, was defeated by an ignoble whelk.

Limpet's tongue.