Stalk microstructure of pseudoplanktonic crinoids

Throughout their long evolutionary history, crinoids developed pseudoplanktonic lifestyles and attached themselves with long stalks to driftwood. This article describes the microstructure and internal morphology of the stalks of such crinoids from the genus Seirocrinus. Although their stalks share some features with benthic crinoids, they show unique adaptations, i.e., large spaces between the columnals. These adaptations reduced the weight of the stalk and increased its buoyancy, likely allowing these crinoids to colonize floating logs across multiple generations.