; subphylum Echinozoa, class Echinoidea)
An order of irregular echinoids which have a compact apical system and a plastron in which the labrum is followed by a pair of large plates. Most spatangoids have narrow bands of densely ciliated spines, which can be recognized in fossils as areas of very small tubercles on denuded fascioles. The Spatangoida first appeared in the lowermost Cretaceous.
Subjects: Zoology and Animal Sciences.