This holdfast, from an unknown species of Glyptocrinus, functioned to attach the stem of the crinoid to the substrate. All Ordovician crinoids were attached to various kinds of substrates, including hard parts of other organisms, hardgrounds, and loose sediment. Some crinoids, called feather stars, are not attached to the substrate, but can crawl or even swim weakly. Such mobile crinoids are found only in Mesozoic and Cenozoic rocks, and there are also many living species.

Detail of holdfast