The Crinoid Cup

The calyx is the main "body" of the crinoid and consists of the dorsal cup and the tegmen. The dorsal cup is constructed of laterally joined polygonal (usually pentameral) plates between the tegmen and the stem. There are two major classes of cups: The monocyclic and dicyclic cups. The monocyclic cups are composed of a single circlet of plates just below the plates from which the feeding arms extend. The dicyclic cups, as you might guess, have two circlets of plates below the arm bearing plates.