A compound ambulacral plate composed of three or more elements of which the lowest is always the largest. Elements between the upper and lowermost elements are all small and do not reach the perradius.
The planktonic larval stage in the life cycle of an echinoid
A compact apical disc in which ocular plates II and IV abut and separate the anterior and posterior paired genital plates (purple).
Part of the Aristotle's lantern; epiphyses are usually hatchet-shaped elements that attach to the distal ends of the hemipyramids and support the rotula (r).
In the posterior interambulacrum, plates 3a and 3b (green), which follow the sternal plates (purple) and form the posterior part of the plastron in many spatangoids.
Microscopic dense, irregular granulation covering the surface of plates never associated with spines or pedicellariae.
A compact apical disc in which genital plate 2 is extended posteriorly between the posterior genital (G1, G4) and ocular (OI, OV) plates.
A compact apical disc in which genital plate 2 is not extended posteriorly between the posterior genital plates.
An arrangement of apical disc plates in which the ocular plates are in contact with the periproct (monocyclic plating).