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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|J. W. Durham and K. E. Caster 1963||Free living, fusiform placoid echinoderms with spirally pleated, expansible test; apical and oral poles at opposite extremities; columns of plates arranged in a spiral; ambulacra and "inter ambulacra" present; new "interambulacral" plates originating at apical pole and becoming more oral in position as subsequent plates are added (origin of ambulacral plates obscure). Lower Cambrian, California|