Fig. 1

Theca of the holocystitid diploporitan Holocystites scutellatus from the middle Silurian Massie Formation of southeastern Indiana, USA (CMC IP 88496), encrusted by a dendritic radicular attachment structure belonging to the camerate crinoid Eucalyptocrinites. A View of the lateral surface of the diploporitan theca with the encrusting crinoid attachment structure near the oral pole (at the top of the specimen in this image). Note that the radices extending down along the surface of the theca are relatively long. Scale bar = 10 mm. B Close-up of the encrusting attachment structure, showing the well-developed radices extending from the oral region toward the aboral region and the essentially invisible radices extending toward the oral pole. Scale bar = 2 mm. C View of the longest radice, displaying dichotomous branching and tapering. This radice extends over most of the lateral surface of the theca. Scale bar = 5 mm