The Crinoid Tegmen
Crinoids were and are feeding animals, which
necessitates a mouth and anus. Like most echinoderms
the crinoids have a one-way digestive tract with a mouth, some sort
of gut system, and an anus. Unfortunately for the crinoids their
mouth and anus are situated side by side within the tegmen.
the anal opening is protected by the
anal pyramid, a plate covered dome protruding from the tegmen.
The tegmen is located on
the dorsal region of the cup, surrounded by the
upward reaching feeding arms. The mouth
is strategically positioned at the base of the feeding arms which
use their ciliated ambulacral grooves
to transport the collected food particles down the arms to the mouth.
While feeding, the tiny cover plates that protect the tegmen and the
many tube feet open up allowing food
to enter the mouth.