Beautiful Shells of New Zealand / An Illustrated Work for Amateur Collectors of New Zealand Marine Shells, with Directions for Collecting and Cleaning them

by Edward George Britton Moss

In many shells, such as the Triton, or Lotorium as it is now called (Plate III.), every increase in growth can be traced in the thick lip formed by the animal when it has increased the size of its shell. Others again, such as the Struthiolaria (Plate IV., Fig. 4), only form a lip when their full size has been attained, and by this the difference between an old and young Struthiolaria can at a glance be seen. Others form a lip at each growth, and then dissolve the lip before starting again. Vertebrate fish are supposed to grow, and increase in size, till the day of their death, but shellfish do not do this. The shell becomes stronger and thicker with age, the animal having the ability to add layer after layer of nacreous, or pearly deposit, on the inside of the shell; and as the animal shrivels and lessens in size the thickness of the shell increases. And some, when they become too large, have power to dissolve the partitions in the shell, and deposit the material on the outside of the shell.

The time it takes a shellfish to grow to its full size varies a great deal. Oysters take about five years; but the giant Tridacna, the largest bivalve in the world, has been found so enclosed in the slow-growing coral that it could hardly open its valves.

The young of most shellfish are active little things, and are usually so different from their parents as to be unrecognisable. Some swim, or frisk about, and travel even long distances in search of suitable quarters to settle in. Others float on the surface, and are driven where the winds and currents list. Some, like mussels, are distributed all over the world, others again are found, perhaps, on one rock, or on one small sandbank in a large district. Many shells are rare, because we do not know where to look for them; but if we know and can find their food, we will find the shellfish not far away. Some change their shape so much that, as they age, they have to dissolve all the partitions made in their youth in the shell. The eggs of some are scattered on the surface of the water, while the eggs of others are hatched by the mother before being turned adrift.

Marine shellfish live in all kinds of places below high water mark; and some of the semi-amphibious ones thrive even above ordinary high water mark, where for days at a time nothing but the tops of the waves could reach them. They are found on seaweed and on rocks, and on sand or mud-banks; but especially in places near rocks on marine grass banks bare at low spring tides. Some live on the surface of the water, some burrow in sand or mud, and some bore holes for themselves in the softer rocks. Some live in deep water; but the better coloured shells are found near low water mark, or in shallow water; for light is as necessary to the perfecting of colour in shells as in flowers. Shells that have grown in a harbour are more fragile than those grown in the ocean, and are usually less brilliant in colour, as harbour water is not as clean as ocean water. The colour of shells (as of insects) depends largely on environment, and is only one, and by no means the most reliable, method of deciding the species. An expert can at a glance tell whether a given shell has come from shallow or deep water, and whether from an exposed or sheltered spot. Most shellfish move about a great deal, and migrate into deeper water in summer; and on bright clear days retire into dark corners amongst, and even under, stones. On a dull day a collector is frequently more successful than on a bright, sunny day; and in spring or early summer the best hauls of live shells can be made. Nearly all shells have an epidermis, or outer skin. In some this is very apparent, as in the Lotorium olearium (Plate V., Fig. 1), or the Solenomya parkinsoni (Plate IX, Fig. 18), while in others it is nearly transparent, and hardly perceptible. To enable the true colours of a shell to be seen the epidermis must be removed.

The supposed original form of a shell was that of a volute univalve, such as the Triton (now Lotorium), or Struthiolaria. To properly enclose the animal, and make it safe from enemies, an operculum, or lid, was so formed that when the animal retired into the shell this filled up the opening. The operculum is usually like a piece of thin, rough brown horn, and where no reference is made to an operculum in this work, it must be understood that the operculum is horny. Some shells, such as the Astralium sulcatum (Plate VI., Fig. 18), and the Turbo helicinus (Plate VI., Fig. 17), have a shelly operculum; that of the latter being the well-known cat's eye.

In some shells the operculum is small, in others large, and progressing step by step we find some, such as the scallop and oyster, with one side round, and the other (really an operculum) flat and as large as the shell; until we come to the perfect type with each valve the same shape and size. Then the operculum disappears, as in the limpet, and the covering shell becomes smaller and smaller, till in the Scutum ambiguum (Plate IX., Fig. 23) the shell bears about the same proportion to the animal that the little bonnet, fashionable a few years ago, bore to the lady that wore it. The shell is built up of very thin layers of nacre, or mother of pearl, and calcareous or chalky matter, the thinner being the layers of nacre the more lustrous and iridescent is the shell.

As would be expected from its isolated position, many of the genera of New Zealand shells are not found elsewhere. The late Professor Hutton mentions nine genera in this position.

The dispersal of shells is an interesting natural phenomenon. The eggs of molluscs are so small that they can easily be carried by currents, attached to floating seaweed or floating timber, on the hulls of ships, or in the feathers or feet of our migratory birds, such as the godwit, which every year travels from New Zealand to Siberia and back. A great many of our shells are found on the Australian coasts; and a surprising number are common to both New Zealand and Queensland.

In describing the illustrations, length means extreme length, and by measuring the shell on the plate the proportionate width can be ascertained. The illustrations are, generally speaking, half the natural length of the shell depicted; and the shell photographed, although in most cases an average full-sized specimen, in some instances was smaller than the average.