Morphology and ultrastructure of Devonian spores: Samarisporites (Cristatisporites) orcadensis (Richardson) Richardson, 1965

Specimens of the dispersed spore Samarisporites (Cristatisporites) orcadens is (Richardson, 1965) have been isolated from Middle Devonian deposits of C romarty, Scotland. This is the strata from which the type material was obta ined (Richardson, 1960) The specimens are extremely well preserved and of l ow thermal maturation. Comprehensive investigations using light, scanning e lectron and transmission electron microscopy provide detailed information o n morphology, gross structure and wall ultrastructure. The spores are trila yered, with a bilayered inner body entirely enclosed within an outer layer. There is apparently no cameration between the layers comprising the spore wall. The outer layer is entirely homogeneous, and is extended forming a tr ilete mark on the proximal surface, a prominent 'pseudozona' in the equator ial region and distinctive distal ornament. The inner body is bilayered, wi th the inner (alpha) layer comprising closely packed, straight, parallel an d continuous lamellae, and the outer (beta) layer comprising similar but le ss closely spaced and more irregular lamellae. The morphological, structura l and ultrastructural information is assessed in order to evaluate the taxo nomic demarcation of this taxon, and also to shed light on spore wall forma tion, functional morphology and affinities/phylogeny. It is suggested that structural interpretation based on light microscope work is susceptible to misinterpretation, because the different layers of multilayered spores ofte n possess different ultrastructure and hence differ in optical properties. (C) 2001 Elsevier Science B.V.. All rights reserved.