1, A lateral view of Hypsiclavus huntsvillensis in the extended position. 2, An aboral view of Hypsiclavus huntsvillensis in the contracted position. P = periproct or anus, M = peristome or mouth, RZ = recumbent zone, PZ = pedunculate zone, PR = peripheral rim.

The pedunculate zone is positioned between the recumbent zone and the peripheral rim. In forms an elaborate stalk when in the extended position, but can also be contracted to bring the oral surface down flush with the substrate. This zone is more highly derived than the condition found in the pyrgate thecal design of non discocystinid agelacrinitids with the circlets of peduncular plates being regularly organized into columns (28-35 in number) and with up to 75 plates in each column. Sutures of these plates are highly imbricate and meet in four-plate junctions (a situation very unusual in Echinodermata).

SEM of a pedunculate zone plate from Spiraclavus nacoensis.