English: Hederella encrusting a Megastrophia fossil brachiopod from the Devonian of Ohio, USA.

This is the exterior of a ventral valve of a moderately large strophomenid brachiopod called Megastrophia. It is a common fossil in the richly fossiliferous Silica Formation of northwestern Ohio and southeastern Michigan. This Middle Devonian unit consists of interbedded shales, calcareous shales, argillaceous limestones, and fossiliferous limestones. Common fossils include brachiopods, bryozoans, crinoids, trilobites, and other typical Paleozoic marine faunas.

The squiggly, vine-like structures are a problematic fossil known as Hederella, a hard substrate-encrusting organism. Hederella was once considered to be a type of bryozoan, or "moss animal", similar to the cyclostomes Corynotrypa and Cuffeyella (those genera occur in the Ordovician-aged Cincinnatian Series of the Ohio-Indiana-Kentucky tristate area). Subsequent study has indicated that Hederella is not a bryozoan at all, but is, or is closely related to, the phoronids, a group of lophophorates.

Stratigraphy: Silica Formation (also known as the Silica Shale), Givetian Stage, upper Middle Devonian

Locality: quarry in the Silica-Sylvania area, far-northern Lucas County, northwestern Ohio, USA