Middle Cambrian; Late Ordovician – Holocene
Crinoidea is an extant class of stationary upper-level epifaunal suspension feeders
Characteristics of the Class
- Well developed pentameral symmetry
- Radial growth pattern concentrated on arms and directed away from the theca
- Theca distinctly divided into aboral cup and adoral tegmen
- Well developed column
- Crinozoa provided with true arms; pentameral symmetry well developed; theca divided into aboral cup and adoral tegmen, comprising five radial plates from which invariably the aboral skeleton of the arms starts; radial growth pattern concentrated on arms, which are directed away from theca; column ordinarily well developed , lost in postlarval stage in some forms.