Middle Ordovician (Mohawkian) – Late Ordovician (Cincinnatian)
Heterocrinidae is an extinct family of stationary intermediate-level epifaunal suspension feeders
Description of the Family
- Small, steeply conical cup
- Anal X supporting longitudinal row of enlarged tube plates
- Elongate anal tube and may be spirally coiled
- one to three primibrachs may be fixed in top part of cup
- Arms uniserial, nonpinnulate, branching isotomously several times
Treatise on Invertebrate Paleontology, Part T (1978):
- Cup small, steeply conical; anal X supporting longitudinal row of enlarged tube plates. Anal tube elongate, may be spirally coiled. Proximal one to three primibrachs may be fixed in top part of cup, rachials occupying full width of radials. Arms uniserial, nonpinnulate, branching isotomously several times.
- Monocyclic (originally perhaps dicyclic), with small, irregularly constructed calyx and long, variously branching arms; basals five, equal; radials five, the right posterior and left anterior bisected transversely into super and inferradials; first anal plate rather large, usually resting on the left and right shoulders of, respectively, the right posterior superradial and the left posterior pradial, always followed by a series of quadrangular plates that forms the support of a long, tubular or spirally coiled ventral sac; rays five, each with two to five primibrachs, the first of which commonly is partly or entirely included in the calyx; arms ten, non-pinnulate, dividing isotomously, heterotomously, or by throwing off long armlets which may divide repeatedly or remain simple.