Perittocrinidae
The Perittocrinids are a
monocyclic group originating in the early Ordovician. This group
is unique for the disparids in having endothecal slits in the
thecal plates. Simms' (1993) phylogenetic analysis of the
disparids suggests that the Perittocrinids are the primitive
sister group to the Hybocrinid and
disparid taxa.