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By Philippe Bouchet, Gilles Mermet
Abbeville PressCopyright © 2008 Philippe Bouchet
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A taxonomist analyzes the characters that are unique to each species. These are the very characters that serve to delimit the species or in other words to define it. In addition, the job of the taxonomist is also to look for characters that are shared with other species, because it is these that will help to place them in a particular clade. The classification is organized in hierarchical that correspond to body structures with increasing levels of dissimilarity. Species are grouped together in genera, genera in families, families in orders, orders in classes, and classes in phyla. Mollusks, as we have seen above, are phylum: the Mollusca. The Arthropods (crustaceans, Insects, spiders, scorpions and so on), the Cnidaria (containing sea anemones, jellyfish, corals, sea fans and so on), and the Echinodermata (sea urchins starfish, brittle stars and so on), are phyla. Within the phylum Mollusca, taxonomists recognize eight classes of gastropods, bivalves (also known as lamellibranchs), scaphopods, polyplacophores (or chitons), cephalopods, monoplacophores, solenogasters, caudofoveates (these last two are sometimes grouped together under the name aplocophores). Gastropods, literally meaning "crawling on their stomach," are by far the most diverse class, with over 400 families containing 75,000 species of snails and slugs.
In view of these colossus numbers, no single book can cover all the species of mollusks, or even all the species of seashells. Even before Linnaeus, naturalists tried to produce comprehensive monographs that would include all species known at the time. Linnaeus needed only just over a hundred pages of his Systema Natunae to list and describe the 700 species of shells known to him. Sixty years later, Jean-Baptiste Lamarck (1744-1829) needed two volumes of Histoire Naturelle des Animaux sans Vertebres( Natural history of animals without backbones) to cover the 3,000 species that had been described by then.
Excerpted from Shells by Philippe Bouchet, Gilles Mermet. Copyright © 2008 Philippe Bouchet. Excerpted by permission of Abbeville Press.
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