Shells of Shellfish
All For The Want Of A Pearl
It's funny how little ordinary things created entirely by nature loom so largely in the backstory of history. It makes you wonder what is it inside of mankind that coveted what non-human creatures are only capable of making -- so much so that man often risked everything to obtain them.
In the writings of Julius Caesar, he gives several reasons why he crossed over from Gaul to attempt to conquer Britain. A late Roman writer, Suetonius says that these were not the real reasons. He claimed that Caesar yearned for the pearls Britain was reputed to possess and that he went there hoping to get them.
They may have sufficed to turn the scale. We know that the only article of spoil Caesar is recorded to have carried home from Britain was a breastplate adorned with pearls, and this he dedicated in the Temple of Victory in Rome.
So that shellfish had an important part in the story of the times which brought Britain out of barbarism.
They were food and implements to the ancestors of many peoples in still earlier times wherever they may have lived, and all over the world today, where civilizations have grown old -- they are the raw material of history.
Whenever we examine prehistoric sites great mounds are found formed of the debris of old-time kitchens. There are bones of the animals the people ate, and among them the shells of shellfish. Even in the absence of bones and implements there old shells in a rubbish mound tell of ancient men and ancient meals.
Taking A Look At the Role of Shellfish In History
There are shellfish, as near to the North and South Poles as water can go. There are shellfish in the tropics. There are shellfish around the shores of every deserted island where seamen have wrecked.
The shells of shellfish, with their contents extracted, are money in various parts of the world, even today. They are personal ornaments in many lands. and emblems of sovereignty in some, and part of religious regalia everywhere.
Yet, we would be wrong to use the word "shellfish", for there is no such thing as a shellfish. The creatures living in shells are not fish. Crabs and lobsters are crustaceans. Oysters, mussels, whelks, snails, slugs, octopuses, and the giant squids -- are all mollusks. About forty thousand species are know, half living today -- and half known only by their remains as fossils in rocks.
In general, the shell of a mollusk is composed of three layers. The outer is a horny substance. The middle consists of prisms of limy substance. The inner layer is a lining of alternating films of different kinds forming a series of microscopic ridges which break up light just as a prism does, so producing the beautiful rainbow effects seen in pearl.
A Humble Unknown Past
We cannot say from what type of creature the mollusks arose. In many of the living classes of life its easy to trace links of relationship. We cannot do that with the mollusk family.
At some time in the past the power was placed at the disposal of the mollusk to pour out, from that fleshy part of its body called the mantle, a fluid which hardens into substances forming the shell. The water animals obtained their supplies from lime contained in the sea and fresh pools. The land animals got their material from mineral matter taken up by plants from the soil.
So armor became the possession of one of the humblest orders of life. The plan prospered amazingly. It made the world safe for these lowly animals in a thousand directions.
Heavy shells came to be homes for animals exposed to perils not only from enemies which hunt by the shore and the shallow depths of the sea, but also against the turbulence of the sea itself, which breaks like thunder on cliff and rock.
We find that mollusks exposed to this kind of violence are defended by massive shells. Mollusks which live in calmer or deeper seas have thinner, lighter shells, as have the animals in our still ponds and streams, and those which move by stealth about the land, subsisting on vegetation.
Six Feet Long Snails
So a huge class of animals had their housing problem permanently solved for them. Each was born to carry its house on its back. The process meant a slow about sure progress through life. Interestingly, some of them even managed to reduce their burden.
We find that the shells of slugs, cuttles, and the rest no longer appear, but have vanished like the limbs of the snake and the hind legs of the whale.
Ancient sunny seas had mollusk forms as big as car-wheels, and with huger sucker mouths. Fossil remains of snails six of seven feet long have been found in England. These old-time monsters were found near Hastings in 1922. They were marvels of natural contrivance,not like modern snails in shape, but long and straight with spirals running around them for the whole of their length. The spirals were sixty feet long when followed through their windings.
The giants among mollusks passed aways, and the mollusks of today fall into three groups:
- There are those whose shells have been reduced to vestiges;
- Those whose shells are single;
- And those whose shells are double.
The two-shelled, as in the oyster and the mussel -- are called bi-valves. The one-shelled are called univalves.
To the gourmand, the oyster is the king of mollusks, but to the naturalist -- for all its beauty of inner shell and its gift of the pearl -- it is a degenerate.
Unlike that curious young gentleman of yesteryear's English speaking children -- Tommy Noddy -- who was all head and no body, the oyster is all body and no head. (Not to be confused with the Tommy Noddy of Bubble Magic fame).
So are all of the two-shelled mollusks. The one-shelled, on the other hand, (snails, winkles, whelks, and the rest) all have heads, eyes, and tongues.
Long Marches At Night
The fresh water mussel is a common object to those who probe the mud at the bottom of a stream, but its real story is nothing short of remarkable. Within the two shells of the mussel is a soft mass of flesh and muscle, a broad, flattened ligament which is called the foot, the flesh mantle which secretes the shell material, powerful muscles for cling the shells, a mouth, gullet, stomach, but no head -- therefore no jaws and no tongue.
The mussel protrudes its powerful muscular foot, fills it with blood to make it swell, then pulls itself down into or along the surface of the mud, which such little haste that its best pace would carry it about fifteen feet in the course of one night, when alone it makes its marches.
In order to obtain food the mussel opens its shells and draws in water by the rhythmical waving of multitudes of tiny hair-like cilia.
These induce a flower of water into the mussel, conveying oxygen and food into the system.
Just like an automobile has inlet valves and exhaust values -- the bivalve has its inlet and outlet.
Not the least notable of the mussel's organs is one yielding a glossy silk-like substance which provides cables with to anchor the animal. These are the strands often seen binding edible mussels to the timbers and metal of our seaside piers.
However, note the astonishing role which the byssus, which is the scientific name for this substance plays in the life-story of the fresh-water mussel.
This animal does not broadcast its eggs as the oyster does. The eggs of a fresh-water mussel are exposed to such dangers that Nature has ordained that the mother shall incubate them within her body.
The eggs hatch in tubular cavities in the gills of the mother. It is an able-bodied little fellow, clad in a triangular coat of shell sharply pointed at both ends, that says farewell to its mother and takes the plunge into open water.
Its first act is to spin a byssus of sticky thread, which floats up in the water. An inquisitive minnow or stickleback fish is attracted and draws near. The byssus adheres to it. The baby mussel has caught a fish, but not to eat.
The little mussel, excited by the contact, rapidly opens and closes its twin shells, and so swims up to its capture. Reaching the fish, it grips with the sharp extremities of its shell and establishes itself more firmly than Hemingway's Old Man of the Sea on the shoulders of Sindbad.
The terrible old ruffian of the story did but seat himself on the children's hero, but the mussel seats itself in the very flesh of its host.
Like A Gall On A Tree
The irritation caused by the hooked shells causes a morbid growth of the fish's flesh, which, developing like a gall on a tree, embeds the little mussel and makes it prisoner.
That is exactly what Mother Nature intends to happen. For three months, the larval mussel rests there, traveling wherever its hose may choose.
At the end of the third month, it is a perfect mussel in miniature, and something happens to rupture the cyst in which it is enclosed, liberating the mollusk, and permitting it to settle down at the bottom of the water placidly to follow the business of the perfect bivalve.
Note: On the other hand, the eggs of the Sea Mussels are cast into the water. These mussels are edible and are good food if the water is pure, but are not much eaten in many countries.
Historic Sea-Spinners Of Silk
The way in which these edible mussels anchor themselves has been turned to advantage by human engineers. When the breakwater of Cherbourg, France's harbor was being made -- the engineers threw tons of live mussels upon the works, and left these strange sea-spinners to bind the parts of the breakwater together with their inimitable silken cordage.
In times past, gloves were also made of these byssus threads, which is also boggling to think of when it comes to man's never-ending use of raw materials.
Today, byssus, which is a wonderful adhesive that is not compromised or changed by water (like synthetic adhesives can be) is being scientifically used by genetic engineers
Identifying All Of The Beautiful Shells Of The World
These pictures of shells of land, sea, and river have been drawn from a nature collection to give some idea of the wonderful workmanship of their humble builders. A single shell is a work of art, but it is only when we see many together that we fully realize the beauty of their form and color. Most of the shells depicted here are European, but some are from the United States.
Invasive Zebra (Quagga) Mussels
A small invader named the Zebra Mussel landed in the United States. A native of Russia, they first appeared in 1988 in Lake St. Clair (between Lake Huron and Lake Erie). Since then, they have been spreading at an alarming rate across the country.
Because their young are small and free swimming they are spread not only by water currents but by man with his boats. Like all mussels they attach themselves to boats, pilings, water intake pipes, and any hard surface -- even to turtles.
Much like invasive plants, they are a serious and costly danger to our native ecosystems. They are currently costing this country millions of dollars each year to control them and keep them from spreading.