title: The role of an organic matrix during the formation of siliceous scales in the heliozoon Actinophrys sol (actinophryida, protista).
abstract: Actinophrys sol is a freshwater heliozoon which has trophic and encysted body forms. During encystment, siliceous scales are laid down in silica deposition vesicles. The scales form one layer of a multi-layered cyst wall. Scale production is described using light microscopy, transmission electron microscopy, scanning electron microscopy, and X-ray microanalysis. Silica is laid down on an organic matrix which is visible prior to silicification and after removal of silica with hydrofluoric acid. Actinophrys sol can be cultured under silica impoverished conditions, with the result that the siliceous plates are absent. The cysts continue to form but are fragile. Silica is not a prerequisite for the processes of encystment and cyst formation.
authors.affiliation: Department of Zoology, University of Bristol, Woodland Road, Bristol BS 8 1 UG, Great Britain; School of Biology, The University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: P J
authors.initials: PJ
authors.lastname: Newman
authors.forename: D J
authors.initials: DJ
authors.lastname: Patterson