Article: Morphology and palaeoecology of a primitive mound-forming tubicolous polychaete from the Ordovician of the Ottawa Valley, Canada

Build-ups of the calcareous tube, Tymbochoos (gen. nov.) sinclairi (Okulitch), occur in mid Ordovician limestones of the Ottawa Valley; the oldest previously known build-ups of calcareous tubes are Devonian. The Tymbochoos build-ups occurred as elongate dune-shaped structures in tidal channels on intertidal flats, and as small isolated pillow-shaped structures on near-shore subtidal shoals. Clustered tubes radiated horizontally from small attachment areas and then grew vertically. Individual tubes widened quickly to a diameter of about 1 mm and then grew cylindrically; irregularly spaced concentric constrictions of the tube wall developed in places into thin anteriorly directed internal collars. Growth forms include (1) a framework of concentrated clumps of densely packed, long vertical tubes, found only in the dune-shaped structures, (2) a sparser concentration of clumps with more loosely packed shorter vertical tubes in the pillow-shaped structures, and (3) scattered tube aggregates. T. sinclairi was probably a primitive suspension-feeding polychaete that fed with short tentacles and was supported by its setae-bearing parapodia against the irregularities of the inner tube surface. Few other species were associated with these Ordovician tube build-ups; exploitation of the intertube environment probably began at the end of the Cretaceous.