Parasitology, Harold W. Manter Laboratory of
Date of this Version
1963
Abstract
In 1945 Simpson wrote: "Phylogeny cannot be observed. It is necessarily an inference from observations that bear on it, sometimes rather distantly, and that can usually be interpreted in more than one way." Certainly this applies to a study of nemic phylogeny where our reasoning is based upon degree of resemblance and subject to confusion by convergence and reversal. Many feel that, because fossil records are lacking, it is of little purpose to indulge in speculation on nemic phylogeny. Nemic taxonomy, however, requires such speculation when it is based upon comparative morphology. Our attempts in taxonomy are really an effort to express phylogenetic relationships. These relationships have developed through time and cannot be understood without extrapolation into the past.
In presenting the modification proposed here, I have largely avoided use of zoöparasitic nemas for which a phylogeny was proposed by Dougherty in 1951. Although these are phylogenetically important, understanding the evolutionary sequence of the so-called "free-living" soil, freshwater, and marine nemas should be attempted first.
Changes in the current concepts are necessary if the classification of the Nemata is to be consistent with the available knowledge of their comparative morphology. The modifications suggested in this paper are based upon studies of the cephalic sensory structures (setae, papillae, and amphids), esophagus (its nuclear arrangement, glands and valves), esophago-intestinal valve, excretory system, reproductive system, and total number of intestinal cells. Some use is also made of the stoma, somatic sensory structures, and cuticular specializations.
Comments
Published in THE LOWER METAZOA: Comparative Biology and Phylogeny, edited by Ellsworth C. Dougherty, Zoe Norwood Brown, Earl D. Hanson, & Willard D. Hartman (Berkeley: University of California Press, 1963): 273-282. Copyright © 1963, the Regents of the University of California. Used by permission.