Pellicle ultrastructure demonstrates that Moyeria is a fossil euglenid

Paul K Strother,Wilson A Taylor,Bas Van De Schootbrugge,Brian S Leander,Charles H Wellman

doi:10.1080/01916122.2019.1625457

Abstract

An earlier proposal of euglenid affinity for the acritarch Moyeria was based primarily on the pattern of bi-helical striate ornamentation as seen in scanning electron microscopy and light microscopy. Examination of specimens using transmission electron microscopy reveals that the ‘striae’ are actually integral components of the microfossil wall itself, corresponding to the pellicle strips of some euglenid species today. A Silurian specimen from Scotland preserves an articulated wall composed of thickened arches and thinner U-shaped interconnecting segments paralleling that seen in some modern photosynthetic euglenids. A second specimen from the Moyeria holotype section (Silurian of New York State) shows fused articulation, again compatible with some extant euglenids. This evidence is sufficient to transfer Moyeria out of the Incertae sedis group, Acritarcha, and into the Euglenida. This proposal helps establish the morphological basis for the recognition of euglenid microfossils and ultimately provides evidence of a lengthy fossil record of the eukaryotic supergroup Excavata.

Highlights

In 1989, Jane Gray and Art Boucot posed the question, ‘Is Moyeria a euglenid?’, in an article that explored the arguments from morphology that supported the identification of the acritarch Moyeria Thusu 1973 as a fossil euglenid (Gray and Boucot 1989)
Even though many authors have tacitly agreed with their conclusion, palynologists continue to refer to Moyeria as an acritarch, i.e. an organic-walled microfossil (OWM) of unknown systematic affinity
The Hagshaw Hills inlier is one of a series of Silurian inliers located along the southern margin of the Midland Valley of Scotland (Figure 1)

Summary

Introduction

In 1989, Jane Gray and Art Boucot posed the question, ‘Is Moyeria a euglenid?’, in an article that explored the arguments from morphology that supported the identification of the acritarch Moyeria Thusu 1973 as a fossil euglenid (Gray and Boucot 1989). Gray and Boucot (1989) used scanning electron microscopy (SEM) to document prominent striae in two specimens from the Burvick Beds (Ludlow) in Sweden and another three specimens recovered from the Tuscarora Formation (Llandovery) in central Pennsylvania, USA. These specimens clearly demonstrated apical whirl reduction, a character that is diagnostic of photosynthetic euglenids today (Leander and Farmer 2000; Leander 2004; Leander et al 2007). Even though many authors have tacitly agreed with their conclusion, palynologists continue to refer to Moyeria as an acritarch, i.e. an organic-walled microfossil (OWM) of unknown systematic affinity

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