Microconchids - a little known group of Carboniferous of the Upper Silesia fossil organisms and their occurrence in the Upper

Abstract

The present article concerns a characteristics of enigmatic encrusting organisms of the order Microconchida (microconchids), similar to polychaetes of the genus Spirorbis, as well as a description of their finds from the Upper Carboniferous of the Upper Silesia region, southern Poland. The microconchids described here may represent the genus Microconchus. Most of the individuals encrust terrestrial flora and bivalve shells, and thus they certainly inhabited freshwater or, at most, brackish water environment. Similarly as the Recent polychaetes of the genus Spirorbis, the microconchids described here occur in association composed of both adult and juvenile individuals. The juveniles, however, dominate, what may indicate they have died due to some stress conditions (high rate of deposition and/or low oxygen content in the water). The microconchids are poorly-preserved. The original calcitic mineralogy of their tubes was replaced by phases similar to lead sulfide and dolomite