SEA-CUCUMBER (Holothuria tubulosa).
We must now examine a most important class of pulpy animals, the Mollusca, [pg 128]of which the bivalve molluscs are by far the most important to man. In consequence of their very softness and delicacy, Nature has provided them with a shell coat of calcareous mail.
The sub-class Acephala, are as their names indicate, headless molluscs, and though sometimes partially naked, are usually very well protected by shells. When it is known that there are over 4,000 species of bivalve molluscs, the impossibility of describing more than a few typical and prominent examples will be seen.
The genus Teredo consists of marine worm-like animals having a special and irresistible inclination for boring wood, whatever its hardness. Ships have been thus silently and secretly undermined, till the planks have been either like sponges or have crumbled into dust under the very feet of their crews. The holes bored by these imperceptible miners riddle the entire interior of a piece of wood, without any external indication of their ravages. Piles and piers have been utterly ruined, and vessels have sometimes gone to the bottom through them. At the beginning of the last century half the coast of Holland was threatened with inundation and practical annihilation because the piles which support its dykes were attacked by the teredo, and hundreds of thousands of pounds damage was done by this wretched worm. It has been now discovered that the worm has a great antipathy to oxide of iron, and wood impregnated with it is secure from its ravages. Other animals of the same group are capable of boring even rock.
Another important bivalve is the well known Solen or “razor-fish,” varieties of which are common all over the globe. “These molluscs,” says Figuier, “live with their shells buried vertically in the sand, a short distance from the shore; the hole which they have hollowed, and which they never quit, sometimes attains as much as two yards in depth; by means of their foot, which is large, conical, swollen in the middle and pointed at its extremity, they raise themselves with great agility to the entrance of their burrow. They bury themselves rapidly, and disappear on the slightest approach of danger.
“When the sea retires, the presence of the Solen is indicated by a small orifice in the [pg 129]sand, whence escape at intervals bubbles of air. In order to attract them to the surface, the fishermen throw into the hole a pinch of salt; the sand immediately becomes stirred, and the animal presents itself just above the point of its shell. It must be seized at once, for it disappears again very quickly, and no renewed efforts will bring it to the surface a second time. Its retreat is commonly cut short by a knife being passed below it; for it burrows into the ground with such velocity that it is difficult to capture it with the hand alone. The fish itself is a kind of marine worm.”
THE RAZOR FISH (Solen ensis).
But of the Acephalous Mollusca none are more important to man than the mussel and oyster, the pearl-bearing varieties of which latter have been already considered. Both are familiar to every reader.
The Mytilus edulis, the edible mussel of commerce, the “poor man’s oyster,” is provided with a byssus, a bundle of hairs or threads, by which it can anchor to the rock. In its natural state it is much less fitted for human food than when cultivated. Their civilisation, as it might be termed, dates back to the year 1236, when the master of a barque, an Irishman named Walton, was wrecked in the bay or creek of Aiguillon, a few miles distant from Rochelle. The exile at first supported himself by hunting sea-fowl in the neighbouring marshes, where he also soon began, being an observant man, to notice certain peculiarities of mussel life.