The Calyx is the cup-like part of the organisms that contains the internal organs of the crinoid. It is a cup-like portion that supports the visceral mass of the crinoid. The rays of the crinoid, which attach the arms, are directly connected to the calyx, which is also known as the aboral cup. The plates of the calyx can by either monocyclic or dicyclic. This refers to the number of rows of plates around the calyx.
Monocylic calyces have two rows and dicyclic calyces have three rows.
The arms of a crinoid extend from the calyx. They serve to filter out plankton from the water. The number of arms on a crinoid may vary tremendously. This may be due to the availability of food, if there is more food, then there is not a need for as many arms. If there is less food then more arms are beneficial to comb the water column.