The holdfast (attachment structure) is the most understudied aspect of the palaeoecology of the endoskeleton of fossil crinoids. A new collection of well-preserved holdfasts from a recently reopened quarry at Hunninge, Gotland, in Homerian (upper Wenlock) strata includes several morphologies. The most common are terminal dendritic radicular holdfasts (TDRHs) that may be derived from the cladid Ennallocrinus d’Orbigny. These have a consistent morphology of five, equally spaced, long radices that spread across the sea floor. These crinoids were gregarious, and TDRHs in a group commonly show the same radice orientations. The radices have a large axial canal compared with those of modern crinoids; each included, at least, nervous tissues. Taken together, these features suggest that, apart from attachment, these distinctive TDRHs may have served a sensory function. Other holdfasts in this assemblage also show monospecific aggregations, perhaps suggesting biochemical attraction such as that shown by certain other sessile invertebrates such as barnacles.