An ambulacral element of a compound plate that contacts the adradial suture but extends only part of the way across the interambulacral column and thus ends before reaching the perradius (in blue).
The narrow platform on the interior of a pyramid that supports the tooth.
diadematid plate compounding
A style of ambulacral plate compounding composed of three or more elements, of which the middle element is the largest. All other elements extend the full width from adradial to perradial suture.
An apical disc in which all of the ocular plates (white) are separated from the periproct by genital plates (purple); the genital plates forming a contiguous ring.
See apical disc.
The calcite platelets or elements that form a rosette to terminal sucker of the tube foot.
disjunct apical disc
An apical disc that is in two parts, separated by interambulacral or complemental plates. As a result, the posterior two ambulacra and anterior three ambulacra converge towards different points on the test.
Plastron plate arrangement in which the first interambulacral plate (red) is separated from the second interambulacral plates (green) by ambulacral plates