Middle Ordovician phosphatic inarticulate brachiopods from Västergötland and Dalarna, Sweden

Phosphatic inarticulate brachiopods are described from Middle Ordovician (Viru Series) strata in Västergötland and Dalarna, Sweden. The material originates from a series of closely spaced samples through the sequences of the Fjäcka and Kårgarde sections, Dalarna, and at Gullhögen quarry, Västergötland. Fifty-six species (34 named, of which 22 are new) are described, assigned to 29 named genera (of which three are new). The new acrotretacean subfamily Biernatinae is proposed, together with the new acrotretacean genera Cyrtonotreta and Biernatia, the problematical genus Tegulella is erected. For the discinaceans and most of the lingulaceans open nomenclature is applied; the taxonomically complicated Family Paterulidae has been excluded from systematic treatment altogether. The lingulaceans and discinaceans share a common type of shell structure which is clearly distinguishable from that of the acrotretaceans. The early ontogeny of many species is described. In the examined members of the Lingulacea and Discinacea the larval shell is large and smooth, whereas the acrotretaceans have a comparatively small and pitted larval shell. Although the protegular stage as a rule is not observable in fossil material, the cementing ventral valves of some eoconulids preserve the mould of an organic embryonic (or early larval) shell. The evolution of the phosphatic-shelled inarticulates is discussed. Within the order Acrotretida (sensu lato) the acquisition of a ventral valve with holoperipheral growth and a pedicle foramen could have taken place convergently several times from a lingulid stock, leading to the acrotretaceans, discinaceans, and siphonotretaceans, respectively; the latter two superfamilies are considered to belong to separate orders, the Discinida and the Siphonotretida. The usefulness of the inarticulates for biostratigraphical correlation is demonstrated.