A PRELIMINARY STUDY OF THE BURGESS SHALE TAXON YUKNESSIA SIMPLEX WALCOTT, 1919 USING BACKSCATTERED ELECTRON IMAGING

Charles Walcott erected Yuknessia simplex in 1919 as a new species of fossil alga based on specimens from the Burgess Shale. The holotype specimen is 14 mm tall and comprises an ovoid basal structure, approximately 2 mm wide, that gives rise to numerous unbranched tubes, each approximately 0.4 mm wide and 9 mm long. In 1988, Conway Morris and Robison identified specimens from the Wheeler and Marjum formations of Utah as Y. simplex. Subsequently, Maletz et al. (2005) examined a specimen with a Yuknessia-like morphology from the Wheeler Formation using backscattered electron (BSE) imaging. These images revealed banding on the tubes of the specimen, interpreted as fusellar structure, and the specimen was described as a cephalodiscid hemichordate. In this study, BSE imaging was applied to additional Yuknessia-like specimens from the Wheeler Shale in the Drum Mountains of Utah and to type-material of Y. simplex from the Burgess Shale (British Columbia). All of the study specimens from Utah show fusellar structure, indicating a hemichordate affinity for this material. Images of Y. simplex from the Burgess Shale, however, lack fusellar structure, a finding consistent with the algal affinity proposed by Walcott and indicating that the material from Utah is not Yuknessia.