Crinoid calyx origin from stem radial echinoderms

Abstract Evidence from the earliest-known crinoids (Tremadocian, Early Ordovician), called protocrinoids, is used to hypothesize initial steps by which elements of calyx evolved. Protocrinoid calyces are composed extraxial primary and surrounding secondary plates (both have epispires along their sutures) that unlike those more crownward fossil extant in equivalent calycinal plating strongly organized. These reductions inspired several schemes name these calyces. However, primary-secondary systems seen protocrinoids first appeared among Cambrian stem radial echinoderms, with primaries representing centers around secondaries were sequentially added during ontogeny. Therefore, protocrinoid represents an intermediate condition between earliest echinoderms crinoids. Position ontogeny indicate certain remained as loss occurred, resulting abutting into conjoined alternating circlets characteristic This transformative event included suppression modification or, commonly, elimination respiratory structures. data subradial plate terminology does not correspond most common usage, but rather, supports alternative redefinition traditional expressions. Extension adoral growth fixed rays preceded Restriction or structures also accompanied this modification. Phylogenetic analyses support crinoid origination early pentaradiate separate blastozoans. Accordingly, all Tremadocian express a distinctive aggregate plesiomorphic apomorphic commonalities; branch within clade, subclass-level clades. Nevertheless, each taxon assemblage expresses at least one diagnostic apomorphy camerate, cladid, disparid