Radial perforations in crinoid stems from the Silurian of Gotland

Radiating intracolumnal canals are a characteristic feature of large (diameter 10 mm or more) crinoid stems from the Silurian of Gotland. They are found in nodals as well as in internodals where the columnal height exceeds one millimetre. They were formed secondarily in the median and distal portions of crinoid stems with pseudocirriferous holdfasts. Intercolumnal canals are found in the distal parts of stems with true cirri regardless of the size of the stem. It is suggested that these canals played an important role in crinoid physiology. The crinoids are believed to have sustained a large proportion of their tissues through cutaneous digestion and uptake of dissolved substances from the surrounding sea water. The intra- and intercolumnal canals increased the surface of the axial canal in relation to volume. They provided a connection between the axial canal and the surrounding sea water, thus facilitating nutrient transport to the tissues.