The pages that follow provide basic information about two subjects that can be richly rewarding whether you follow them for profit, as Shell does, or for pleasure, as millions of people around the world do.
SEASHELLS. . .WHAT ARE THEY?
First, a seashell is one of the 100,000 species of backboneless animals belonging to the zoological group known as the Mollusca. Mollusks include not only the familiar clams, scallops and snails, but also the squids, octopus and Chambered Nautilus. Other "shells" found in the ocean include those of crabs, lobsters, barnacles and sea urchins.
True molluscan shells come in two main varieties: BIVALVES and UNIVALVES. Bivalves have two valves, fitting together along a toothed hinge on one side, and kept closed by means of ADDUCTOR MUSCLES. Univalves have only one shell, usually coiled, but sometimes shaped like a cap or miniature volcano. Some marine univalves can seal themselves inside with an operculum, which covers the open end of the shell like a trap door. Although shells take on many different shapes, they are much alike inside. Each has a foot, a breathing siphon, a tiny brain and heart, and a fleshy mantle which secretes lime for shell-building. Most true mollusks have eyes, but a few are blind. Many have teeth, called RADULAE.
Like any other animal, the mollusk generally moves about. It pushes along on the ocean floor on its foot, or it might swim a little. It lays millions of eggs and hatches countless baby mollusks. It lives its life in its shell, lugging it around, snuggling into it when alarmed, burrowing into mud, fastening itself to a rock and creating ingenious camouflage. It builds its calcareous house with a great instinctive talent for color and sculpture. . .and the closer it lives to the tropical zones, the more beautifully spectacular is its art.
The two parts of a bivalve shell are like thin saucers, concave inside, convex outside. The inside is smooth, polished. The outside is rougher, sometimes with graceful ribs or concentric ridges or combinations of both. Univalves are conical and spiraling, with a series of whorls coming down like widening steps from the tiny nucleus on top. Univalves may have spines on their shoulders. The opening, called the aperture, has a delicate right-hand rim called the lip and a heavy, left-hand edge called the columella.
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BIVALVE'S anatomy: a) foot, b) adductor muscles, c) gills, d) hinge, e) adductor muscles, f) siphon, g) stomach, h) mantle. Oysters, clams, mussels all have them.
UNIVALVE'S anatomy: As before, a) foot, b) siphon, c) mantle, but also d) operculum. Univalves include whelks, winkles, conchs.
Chambered nautilus is brother to the octopus, but he wears his castle permanently—and on the outside.