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, all characterized by their sphaeroidal, pylomate vesicles bearing conspicuous and distinctively laminate processes. Process marphology - pivotal to peteinoid taxonomy at genus and species levels - is analyzed in detail. It provides the main basis for taxonomic revisions and innovations, as follows: emendation of above three genera; institution of two new species, P. angustilaminae and P. eximium; elevated (subspecific to specific) status, new combination, and emendation of L. hypertrophicum (Eisenack, 1976); new combination and emendation of L. intermedium (Eisenack, 1976); emendation of P. bergstroemii Staplin, Jansonius & Pocock, 1965 (type species), P. velatum Kjellstrom, 1971 (neotype designated), L. kaljoi Uutela & Tynni, 1991 (type species), and C. auriculatum Uutela & Tynni, 1991 (type species); the new combinations L. pennatum (Deunff, 1977) and Ordovicidium asperum (Kjellstrom, 1971); and designation of a new neotype for P. trifurcatum (Eisenack, 1931 ex Eisenack, 1938) Eisenack, 1969. A comprehensive and critical literature survey reveals, inter alia, that certain species pre1:iously 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. All three genera are confined to the Ordovician. From current records, Peteinosphaeridium extends from the lower into the upper Ordovician uppermost Tremadoc-upper Ashgillj; both Liliosphaeridium and Cycloposphaeridium are considerably more restricted stratigraphically (upp, A renig-lower Llanvirn and uppermost A renig-mid Llanvirn respectively). Previously inferred, acritarch-based, biogeographic provinces for tl lower and middle Ordovician are well-substantia?ed by the peteinoid evidence, in particular the differentiation of the Baltic Province from the Perigondwana Province, with different species of Peteinosphaeridium characterizing each and Cycloposphaeridium confined to the former. However, few data are available from South America, North America, North China, and Australia.