; phylum Echinodermata, subphylum Crinozoa)
The most primitive living class of echinoderms, whose members have a long stalk (or, rarely, are sessile without a stalk, or free-swimming), a calyx (lower surface) composed of regularly arranged plates, well-developed, movable arms, mouth and arms on the upper surface, radial food-grooves on the arms, leading to the mouth, and tube feet on the arms. The more primitive types are attached to the sea floor by stalks, the more highly evolved types are free-swimming. Crinoids are known with certainty, as Eocrinoidea, from the Early Ordovician onwards, and were fully modern by the end of the Palaeozoic.
Subjects: Earth Sciences and Geography — Zoology and Animal Sciences.