External Morphology of Larvae of Chordodes morgani (Nematomorpha)

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The surface features of larvae of a gordian worm, Chordodes morgani (Gordioidea), studied by scanning electron microscopy, were compared to those of other larval nematomorphs, until now known only from light microscopical studies. Larvae of C. morgani have a cylindrical body with 22 to 24 superficial segments, superficially divided at an ectodermal septum into a presoma and a trunk with a roughly 90? bend. Papillae are located distally on the proboscis, the base of which is surrounded by circles of spines or scales. Although the major features of the larvae are similar to those known in other species, details visible with SEM hold promise for providing useful diagnostic characters. Additional key words: horsehair worm, gordian worm Several electron microscropical studies have described adult features of gordian worms (e.g., Zapotosky 1971; Eakin & Brandenburger 1974; Chandler & Wells 1989) and others have treated the ultrastructure of larval forms (e.g., Zapotosky 1974, 1975). Less attention has been given to external features of larval forms (e.g., see Hyman 1951; Poinar & Doelman 1974), and such studies to date have been based on light microscopy. Our objective was to examine, using scanning electron microscopy (SEM), the external morphology of larvae of Chordodes morgani in order to document features that might be used as diagnostic characters, and to better understand their biology. Descriptions of adults of Chordodes morgani MONTGOMERY 1898 were augmented and C. morgani synonymized with C. puerilis MONTGOMERY 1898 by Montgomery (1901). Camerano (1915), in his revised monograph on gordian worms, published important diagnostic features characteristic of adults of C. morgani. Chandler (1985) reviewed the taxonomy and distribution of this species in North America.