[2] However, the clade Olfactores was first proposed as part of the calcichordate theory,[3] and has since been validated through genetic sequencing, albeit without the involvement of mitrates.
However, later revisions of the theory had each separate lineage losing its calcitic skeleton independently,[6] as it evolved from its own mitrate ancestor, making the chordates a paraphyletic group[citation needed].
This would explain the bizarre embryology of Amphioxus, a basal cephalochordate widely held to be the prime example of a chordate bauplan.
[9] The calcichordate hypothesis has been disproven as of 2019; exceptional preservation of soft tissues in the single appendage of the stylophorans Thoralicystis and Hanusia revealed clear traces consistent with a water vascular system—an ambulacral canal with tube feet—covered by movable plates, where the calcichordate hypothesis would require the anatomy be a tail containing a notochord protected by fixed plates.
The enlarged area at the base of the appendage, which in the calcichordate hypothesis would contain muscles to move the tail, contains an extension of the body cavity.
Stylophorans are classed as echinoderms based on their possession of at least two shared and unique features (apomorphies) of the phylum; stereom plates and a water vascular system.