National Geographic : 1949 Jul
The National Geographic Magazine National Geographic Photographer Willard R. Culver Shells as a Decorative Motif for the Home Between two rooms of her Miami Beach winter residence Mrs. John Oliver La Gorce, wife of the Associate Editor of the NATIONAL GEOGRAPHIC MAGAZINE, has fitted glass shelves for her collection. A polished Chambered Nautilus (page 65) is at the center near her right shoulder. At the top to the right of the coral are: a Partridge Tun Shell, a Measled Cowry (page 45, No. 6), and a Trochus niloticus (page 68, No. 15). Two Helmet Shells are to the left of the starfish above her head, and to the right are the Fighting Conch (page 45, No. 9) and the Triton's Trumpet (pages 67, 68, and 80). Below her right hand, to the left, are two Left-handed Whelks (page 45, No. 7). On the bottom shelf two Queen Conchs flank the fan corals. a visible shell-is typical of the humble aspect of mollusks. Nevertheless, to the person with a biological turn of mind this is one of the most thrilling divi sions of animal life. The mollusks are a clear-cut classification and not to be con fused with shellfish generally. For example, the sea urchin (phylum Echinodermata) has a shell with a wonderful pattern. But the urchin, like its near relative the starfish, is built with radial symmetry. Its struc ture radiates like the spokes of a wheel, while the mollusk animal has bilateral symmetry; that is to say, he tends to be long and two-sided like a worm. The shell of a sea urchin is a single layer, growing all over its body all at once. You can see at a glance that this shell is an entirely different texture from that of the mollusk. The crab, lobster, and shrimp (Crus tacea) also have conspicuous shells. This group is distin guished by its jointed limbs and segmented antennae and other parts, while the poor little mol lusk is just a soft unsegmented creature. The shell of the crab also is a single layer, growing only in thickness. That of the mollusk is usually three layers, built by being added to gradually at one end. Moreover, the crab shell is cast off and renewed period ically, while the mollusk shell is a permanent covering. The difference in texture be tween a crab or lobster shell and that of a snail or oyster is easy to see. The crab shell con tains about 15 percent phos phate of lime mixed with the basic carbonate of lime. The mollusk shell, however, has only a trace of the former. It is the carbonate of lime which pro duces porcelainlike shells with enameled surfaces, as in the aristocratic cones, volutes, and cowries, or layers of mother-of pearl that glow on the inner sides of the mussel, abalone, and oyster.