Abstract

An unusual carbonate skeletal organism is found in abundance in the upper of two archaeocyathid-rich horizons in the Lower Cambrian Forteau Formation of southern Labrador. The commonly cryptic organism consists of splaying and branching irregularly polygonal tubes which are open. Tabulae and dissepiments are absent; the walls are thick (200–950 μm) in relation to the diameter of the tubes (150 μm to 5 mm). Only very rarely is wall microstructure preserved. It consists of elongate calcite crystals perpendicular to the wall margin in vertical section. The wall is covered by a thin (20–35 μm) outer layer. Pore-like structures with curved necks are very rarely found perforating the wall outer layer.The affinities of this organism are unknown, but it does have features which are both coral-like and sponge-like. It is here placed in the Incertae Sedis.

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