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Adapations of Respiratory Systems of Spiders

Herbert W. Levi
Evolution
Vol. 21, No. 3 (Sep., 1967), pp. 571-583
DOI: 10.2307/2406617
Stable URL: http://www.jstor.org/stable/2406617
Page Count: 13
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Adapations of Respiratory Systems of Spiders
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Abstract

1) The presence of lung covers does not necessarily indicate the presence of lungs as has been assumed by paleontologists. Lung covers may be retained as vestiges, the lungs having changed into tracheae or disappeared. 2) In the few spiders in which the respiratory organs of both the eighth and ninth segments have stayed in an anterior position (Orthognatha, Dysderoidea), the respiratory organs of the ninth are book lungs or functional tracheae. 3) In the few other spiders in which the respiratory system of the ninth segment are large tracheae, the spiracle migrates posteriorly, during ontogeny, then may move forward again in the adult. 4) The tracheae are derived from transformed lungs (or sometimes from tracheal apodemes) and wherever elaborate are probably more efficient respiratory structures than the book lungs. Physiological data to support this is lacking. 5) In small spiders in which water loss is a hazard, the book lungs of the eighth segment are usually reduced and often transformed into tracheae or completely lost as respiratory organs (as in some Oonopidae). Sun-loving spiders may have more tracheae than spiders living in moist ground or under leaves of vegetation. The few marine spiders and the freshwater spider Argyroneta have an elaborate tracheal system, presumably an adaptation to their unusual habits. 6) Because the presence of well-developed tracheae and absence of book lungs seem to represent adaptations of various groups of spiders, respiratory organs cannot be considered to have phyletic value and cannot be used in classification at the family level. (Exceptions are seen in the Orthognatha and Dysderoidea. The tracheae of the larger Dysderoidea may represent a phylogenetic character inherited from smaller ancestors.) This conclusion is in agreement with the opinion of many arachnologists and with the general systems of classification now in use. It is in contradiction to the classification first proposed by Petrunkevitch in 1933 and used again in his summary of fossil spiders (1955).

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