Ordovician acritarch genera Peteinosphaeridium, Liliosphaeridium, and Cycloposphaeridium: morphology, taxonomy, biostratigraphy, and palaeogeographic significance

Lower to middle Ordovician marine strata of Oland, Sweden, contain abundant acritarch palynofloras especially notable for their diversity and excellent preservation. Quantitatively and qualitatively significant components include representatives of the peteinoid genera Peteinosphaeridium Staplin, Jansonius & Pocock, 1965, Liliosphaeridium Uutela & Tynni, 1991, and Cycloposphaeridium Uutela & Tynni, 1991. Process morphology - pivotal to peteinoid taxonomy at genus and special levels - is analyzed in detail. It provides the main basis for taxonomic revisions and innovations. A comprehensive and critical literature survey reveals that certain species previously attributed to Peteinosphaeridium are not, or may not be, so assignable. The geographic and stratigraphic distributions of all species judged to be authentic or likely representatives of the three genera are documented. -from Authors