A Lingula-Heliolites Association from the Silurian of Gotland, Sweden

In the Silurian Hemse Group (Ludlovian) of Gotland, Sweden, Lingula occurs in burrows in Heliolites interstinctus Linnaeus and rarely in Densastroma podolicum (Yavorsky). Statistical analysis of patterns of burrow occupancy and mode of burrow construction suggests that Lingula did not make the burrows, but occupied them after they were abandoned by the burrowing organism. Lingula preferred to occupy burrows in living Heliolites colonies, and was usually able to keep the burrows open in spite of continued coral growth. The relationship is interpreted as commensal, benefiting Lingula by providing a solid substrate and perhaps nematocyst protection from would-be predators. The virtual restriction of the relationship to Heliolites is attributed to the open structure of the Heliolites skeleton and its slow growth, as compared with the other available colonial coral, Favosites.