Some Late Ordovician bryozoans contain trace fossils called bioclaustrations, raised mounds with a hole in the center built by the bryozoan around a soft-bodied, worm-like organism. A similar system with filter-feeding polychaete worms living in bioclaustrations on modern bryozoans has been observed but is poorly studied. This paper analyzes the relationship between bryozoans and bioclaustrated worms from the Late Ordovician using modern analogs to determine whether they were mutualistic, parasitic, or commensal. Feeding assays showed that modern bryozoans fed significantly better when next to a filter-feeding polychaete worm. Colony fragment size decreased significantly as bioclaustration density increased, possibly due to growth stunting or a weakening of the exoskeleton and therefore increased breakage during preservation. A typology of bioclaustrations was made based on morphology observable under a hand lens. Bioclaustration type did not correlate with bryozoan genus, suggesting that the bioclaustrated organisms determined the shape of the bioclaustration and that they could live with a wide range of bryozoan hosts. More work is necessary to determine the nature of this symbiosis.


Wilson, Mark




Paleobiology | Paleontology


Cincinnatian, Ordovician, Bioclaustration, Bryozoan, Symbiosis

Publication Date


Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis



© Copyright 2015 G. William M. Harrison IV