Demosponges as substrate: An example from the Pennsylvanian of North America

The rigid skeletal frameworks of two heliospongid genera from the Bethany Falls Limestone (Pennsylvanian) of Missouri provided suitable sites of attachment for other marine invertebrates in a quiet water environment. A cluster of three horn corals attached apically to one Heliospongia while it was upright. Other horn corals are in lateral contact with ?Coelocladiella fragments and may have attached to fallen specimens. The distribution of acrothoracic barnacle borings and membraniporiform bryozoans on ?Coelocladiella fragments suggest that the sponges were in an upright position when the epizoans lived. Calcareous worm tubes and shell scars of Derbyia are also associated with ?Coelocladiella. The sponges themselves became established on a soft carbonate mud bottom by growing on productacean shells and possibly fallen blades of calcareous algae. Irregularities in their form indicate that conditions were crowded on limited sites of attachment. The organisms in the assemblage are ecologically coherent and in situ. Ecological requirements of associated organisms and sponge morphologies indicate: (1) the energy of the environment was low to moderate, (2) the rate of deposition was slow and (3) the substrate was a soft carbonate mud.