THE Mollusca vie with the insects, among the backbone-less animals, or invertebrates, in their abounding numbers and more particularly, in the extreme variety of situations in which they are found; in and on the ground, on lowland and highland, in marsh, moor and heath; in pond, stream and river, on the shore, in shallow water or in the abyssal depths of the ocean in every sea the world over. Yet for all their abounding numbers the Mollusca are of surprisingly little
direct use to man. Some like the oysters, mussels and cockles serve for food, but even these are, in civilised countries at least, to be counted as delicacies. Cuttlefish also are eaten in some parts of the world. Apart from this, however, molluscs merely supply pearls and mother-of-pearl, for buttons, studs and such things.
Surprisingly enough it is the mussel that should be looked upon as the greatest benefactor to man, if such a phrase may be used for unwitting service. In addition to its value as food and as a bait in long-line fishing, its strongly gregarious habit and method of attaching itself to timber and masonry have a quite unexpected value. The byssus, the tangle of brown threads by which a mussel is attached, serves to bind the sand and mud, and mussel-beds are often an important factor in preserving the foreshore against the shifting action of tides and currents. The masses of mussels on breakwaters, pier-piles and quaysides also serve as fenders against the force of the waves. Although this can hardly be quoted as a case of direct use to mankind, it is interesting to recall, if only to illustrate its strength in relation to its power to bind a shifting foreshore, that the threads of the byssus have occasionally been used to weave a cloth from which small articles of human apparel, such as gloves, can be made.