Armoured annelids and molluscs from the Upper Ordovician Boda Limestone, central Sweden

摘要

Sclerites of machaeridians (Annelida) and polyplacophorans (Mollusca) from the Upper Ordovician (Katian–Hirnantian) Boda Limestone of the Siljan district, central Sweden are described for the first time. Four taxa of machaeridians were found, but with one exception they are either known from a single isolated sclerite or only one type of sclerite. The largest taxon is represented by an inner modified sclerite of Plumulites sp. A from Osmundsberget Quarry. The complete scleritome is estimated to have reached a length of 12–15 cm. A more diverse material allows the description of Plumulites eueides sp. nov. from Kallholn Quarry. Within smaller cavities in Solberga Quarry minute sclerites of two taxa were found; Lepidocoleus sp., and Turrilepas sp. The latter record represents the third known Ordovician occurrence and the youngest from that period. Association with minute blind trilobites and concentrations of tiny articulated ostracodes suggest that these small cavities represented cryptic habitats. Two polyplacophoran sclerites are also described: one intermediate sclerite of Chelodes sp. A from Jutjarn Quarry, with only the outer surface exposed, and one intermediate sclerite of Spicuchelodes?sp. from Kallholn Quarry, with only the inner surface exposed. These represent rare examples of Ordovician chitons recorded from outside Laurentian terranes.