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
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.