The Crinoid Stem

The stems of crinoids are a stack of interlocking disks or columnals of a variety of shapes. Often the columnals are arranged in a repeating series of smaller disks periodically interupted by larger cirri bearing columnals. Cirri are hair-like protrusions constructed much like a stem but with smaller columnals. Each columnal is centrally perforated creating a stem lumen leading into the coelomic cavities housed in the calyx. The stems of crinoids end in a variety attachment structures. Some have a root-like system of cirri while others utilize a cementing disk to attach to hard substrates. There are crinoids that have an anchor-like holdfast while others produced bulbs.